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Identifying predators at nests of small birds in a New Zealand forest
Abstract
Time-lapse video equipment was used to film continuously at nests of two small passerines, the New Zealand Robin Petroica australis and the Tomtit Petroica macrocephala, in an indigenous broadleaf/hardwood forest in central North Island, New Zealand. The nests were illuminated with infrared light to allow night-time observations of predator and parent bird behaviour, and signs left at nests were linked to predator identity. Introduced Ship Rats Rattus rattus and the small native owl or Ruru Ninox novaeseelandiae were filmed preying on eggs or chicks on 12 occasions, and Ship Rats scavenged on eggs on two occasions. Parent birds sometimes altered the signs left at nests after predation, which confused identification of the predator, while Ship Rat scavenger and predator signs were indistinguishable. This suggests that attempts to identify predators from nest signs could be misleading and potentially a widespread problem. Time-lapse video filming with infrared illumination is potentially the least biased method of identifying predators, but it is expensive and so is best used in conjunction with simpler methods. This study found no evidence that filming altered predation rates or that the predators or parent birds reacted strongly to the camera or lights, so we believe that filming is a valuable and safe technique to guide management for the recovery of critically endangered species that are threatened by predators.
... The identity of predators that have preyed on eggs, chicks and adults at nests of various bird species has been inferred using various methods. These include carcass lesions , sign at nests (Moors 1983), teeth/bill marks on artificial eggs (Boulton & Cassey 2006), hair left on adhesive tape (Major 1991), and still and video photography (Brown et al. 1998;Sanders & Maloney 2002;Williams & Wood 2002;Stake et al. 2004). Video recordings provide the most definitive evidence of predator species identity and other causes of mortality. ...
... Video recordings provide the most definitive evidence of predator species identity and other causes of mortality. While video investigations in the field have previously been expensive and labour-intensive (Brown et al. 1998), digital camera technology has greatly reduced costs by extending recording time and reducing power requirements (Reif & Tornberg 2006;Parker et al. 2008). Observer effects, caused by cameras at nests, on predator and prey species are a potential danger with this method. ...
... Ship rats have been videoed taking eggs from nests of small passerines in New Zealand (Brown et al. 1998) and were identified as predators of black-fronted tern eggs in this study. Norway rats have been videoed eating carcasses of black-fronted tern chicks in the Ohau River (Keedwell 2003) but not visiting the nests of braided river birds (Sanders & Maloney 2002). ...
Predators at black-fronted tern (Chlidonias albostriatus) nests on the Wairau braided riverbed in Marlborough, New Zealand, were identified using (1) mtDNA analysis of 438 swabs from shell remains, nest contents, and carcass remains, and (2) digital video surveillance of 85 nests. DNA analysis suggested harriers (Circus approximans) were the main predator of tern eggs (171 of 192 shell samples containing predator DNA). Cats (Felis catus) and stoats (Mustela erminea) were the probable predators of the majority of adult terns killed (9 and 8 respectively, of swabs from 19 carcasses). Video results were broadly, though not entirely, consistent with the DNA results, and showed that harriers were the main predator of eggs (9 of 19 videoed predation events), followed by Southern black-backed gulls (Larus dominicanus dominicanus; 3/19); hedgehogs (Erinaceus europaeus occidentalis; 2/19), ship rats (Rattus rattus; 2/19), pied oystercatchers (Haematopus finschi; 2/19) and stoats (1/19). DNA was analysed from nine of the 19 videoed nests but the only predator DNA obtained was from harriers (four nests). Sixty-four percent of depredated nests (683/1063) contained no eggshell remains at the next monitoring visit after predation. DNA analysis of nest material from 71 of these empty nests yielded only one predator result; video footage was therefore essential to identify the cause of 12 empty nests at 19 videoed nest predations. Terns removed the depredated egg remains from eight nests; black-backed gulls consumed eggs at three nests; and a stoat carried the eggs away from one nest. Hedgehog DNA was not found on shell remains from nests with videoed hedgehog predations. Analysing DNA from eggshell and carcass remains is a valuable new tool in wildlife research and management because it can identify predator species and indicate their relative importance. However, our results show that predator species are not equally detectable using this technique, leading to biases in the DNA results. This 'detectability bias' needs to be further quantified, and recognised when interpreting DNA results.
... The idea that parental nest activity attracts predators assumes that predators are visually-oriented and diurnal when birds are active (Roper and Goldstein 1997), but evidence is mixed. Some studies suggested that most predation events occur at night by nocturnal predators (Roper and Goldstein 1997, Brown et al. 1998, Stake and Cimprich 2003, Carter et al. 2007, whereas other studies suggested that most nest predators are diurnal (Thompson et al. 1999, Robinson and Robinson 2001, Robinson et al. 2005, King and DeGraaf 2006, Libsch et al. 2008, Weidinger 2010, Schaaf et al. 2018). Many studies have used cameras to examine nest predator identities, although not necessarily to identify diurnal vs nocturnal predators and visual orientation as expected under the Skutch Hypothesis (DeGregorio et al., 2016). ...
... Therefore, the Skutch Hypothesis is an important issue to understand given the importance of both parental care strategies and nest predation to fitness (Clutton-Brock 1991, Martin 1996, 2015, Remeš et al. 2012, Matysioková and Remeš 2018. However, arguments about nest predation timing and types of predators have raised questions about the general importance of the Skutch Hypothesis (Roper and Goldstein 1997, Brown et al. 1998, Stake and Cimprich 2003, Carter et al. 2007. In support of the Skutch Hypothesis, we found that the vast majority of nest predation events were during the day, and nearly all nest predators were visually-oriented in a montane tropical bird community in Borneo (Figure 2). ...
The Skutch (1949) Hypothesis that nest predation risk constrains parental nest activity has important implications for the evolution of parental care strategies, but the required conditions for the hypothesis to operate have been questioned. We found the necessary conditions existed in a montane tropical bird community where 95.4% of predation events (n = 456) occurred during daylight hours and almost all predators (n = 224) were visually-oriented. Moreover, incubation strategies for 21 passerine species were explained by nest predation rates as proposed by the Skutch Hypothesis. Hourly rates of visits to the nest were lower among species with higher nest predation rates, and achieved in part by longer on- and off-bouts. Incubation attentiveness (percent of time incubating) does not necessarily affect parental nest activity and was not related to nest predation rates. Nest predation rates were greater in enclosed- than open-nesting species, counter to long-standing views. Moreover, nest predation was usually higher in the nestling period when parents were more actively visiting nests than during incubation for enclosed- but not open-nesting species. This increase in nest predation in the nestling period for enclosed-nesting species might indicate proximate predation responses to parental nest activity that underlie the evolutionary patterns. Adult mortality also can exert selection on evolved strategies. Following life history theory, annual adult mortality probability explained residual variation in incubation behaviors, while accounting for nest predation, with longer-lived species exhibiting lower nest activity and attentiveness. Ultimately, the conditions for the Skutch Hypothesis were clear and evolved behaviors suggest an important influence of natural selection by nest predation in this montane tropical bird community. At the same time, different patterns of nest predation between open- and enclosed-nesting species emphasize a need for further research into how parental nest activity interacts with nest type to affect predator detection of nests.
... In addition, studies usually involved only one or two species, or took place over a single breeding season (e.g. Brown et al. 1998). There are exceptions, however, such as the comprehensive study by Holmes (2011) and that by Pietz and Granfors (2000) which involved 10 passerine species. ...
... It was important to establish that the cameras did not affect nesting success. Our analysis showed that this was indeed the case, which is in line with other studies (Brown et al. 1998;Pietz and Granfors 2000). ...
For most passerines, nest predation has a major impact on breeding success; however, information on the identity of nest predators is scant. In 2012, we investigated the identity of nest predators that each year depredate about 50% of the nests of 21 species in a south-east coastal bird community in New South Wales, Australia. The current study is a 2-year extension of this study and shows that at this study site (a) predation accounts for at least 90% of nest failures, (b) identified nest predators comprised two reptiles, nine birds and five mammals, (c) the suite of predators changes each season, (d) the two major predators were the Eastern Whipbird (Psophodes olivaceus) and the Fan-tailed Cuckoo (Cacomantis flabelliformis), (e) the impact of the Red Fox and Feral Cat was minimal, and (f) there was a variable and complex interaction between the parasitic cuckoos and their hosts. The data show definitively the overwhelming importance of nest predation on fledgling production, and bring to light new and important data on several aspects of the suite of nest predators.
... Because of inherent disadvantages of other methods, video has recently been used to monitor nests (e.g., Brown et al. 1998, Thompson et al. 1999, McQuillen and Brewer 2000, Pietz and Granfors 2000, McCallum and Hannon 2001. Time-lapse, infrared video equipment allows continuous observation of nests and provides indisputable evidence of predator identity. ...
... Other researchers working with video ( Brown et al. 1998, Thompson et al. 1999, Pietz and Granfors 2000) or still cameras (Farnsworth and Si- mons 2000) have come to similar conclusions, although questions remain as to whether cameras attract certain predators while repelling others. We found no evidence of predators using cameras as perches and they apparently gave the cameras no special attention during visits to nests. ...
We monitored 142 Black-capped Vireo (Vireo atricapillus) nests at Fort Hood, Texas, from 1998 to 2001 using time-lapse infrared videocameras to identify nest predators. We recorded 59 predator visits (where at least some of the nest contents were removed or destroyed), resulting in 48 depredated nests. Snakes and fire ants (Solenopsis spp.) were the leading predators, accounting for 18 (38%) and 15 (31%), respectively, of all depredated nests. We also identified a variety of avian (19% of depredated nests) and mammalian predators (11% of depredated nests). Despite intensive Brown-headed Cowbird (Molothrus ater) removal at Fort Hood, we recorded nine predator visits by females of this species, but only one resulted in nest failure. Although predator visits occurred at all hours, most (58%) took place at night. The daily predation rate was higher during the nestling stage than during incubation, partly due to the apparent inability of fire ants to prey upon vireo eggs. We monitored 435 nests without video; field assistants checked the contents of these every 4–5 days. The daily survival rate of these nests was not higher than the rate of nests monitored with video, evidence that video monitoring does not increase nest predation relative to monitoring by human visits to nests.
Uso de Video para Observar la Depredación de Nidos de Vireo atricapillus
Resumen. De 1998 al 2001 monitoreamos 142 nidos de Vireo atricapillus en Fort Hood, Texas. Utilizamos cámaras de video de luz infrarroja para identificar a los depredadores de los nidos. Logramos grabar 59 visitas de depredación (donde al menos parte del contenido de los nidos fue removido o destruido); en éstas, 48 nidos fueron depredados. Los principales depredadores de los nidos de V. atricapillus fueron las serpientes y las hormigas de fuego (Solenopsis sp.). Del total de nidos depredados, 18 (38%) fueron depredados por serpientes y 15 (31%) por hormigas. También identificamos otros depredadores como algunas especies de aves (19% de los nidos depredados) y mamíferos (11% de los nidos depredados). A pesar de la campaña intensiva de erradicación de Molothrus ater en Fort Hood, registramos 9 visitas de depredación por parte de hembras de esta especie, pero sólo una de estas visitas resultó en el fracaso del nido. Aunque las visitas de depredación se dieron en cualquier momento, la mayoría (58%) ocurrió durante la noche. La tasa diaria de depredación fue más alta durante la etapa de crianza que durante la etapa de incubación, en parte debido a la aparente inhabilidad de las hormigas de fuego para depredar los huevos de Vireo atricapillus. Durante nuestra investigación, monitoreamos 435 nidos sin cámara de video; los asistentes de campo revisaron el contenido de estos nidos cada 4 ó 5 días. La tasa de sobrevivencia diaria de estos nidos no fue más alta que la de los nidos monitoreados con cámaras, mostrando que el monitoreo con éstas no incrementa la depredación de nidos con relación al monitoreo por visitas personales a los nidos.
... During the incubation period, we assumed egg predation by Ship Rats if eggshell fragments were found in the nest cup and if the whole eggs were lost from the nest, with no fragments found below the nest (Brown et al. 1996, Innes 2001. We inferred egg predation by Japanese Weasels if eggs with a hole in the side were found inside or below the nest (Nakamura 1997). ...
... During the nestling period, we inferred nestling predation by weasels or cats if we found damaged, displaced nests without nestlings. We assumed predation by rats if nestling remains with chewed flesh ⁄ bones were found (Brown et al. 1996, Innes 2001). However, we could not identify the predators of nestlings if all the nestlings disappeared without any evidence left around the nests. ...
Appropriate nest-site selection is one of the most important ways to minimize loss of reproductive investment due to predation. We determined the environmental characteristics associated with nest predation during the incubation and nestling periods of arboreal nesting Bull-headed Shrikes on the oceanic Minami-Daito Island where the predator community has low species diversity and includes only three introduced mammals: Ship Rat Rattus rattus, Japanese Weasel Mustela itatsi and Feral Cat Felis catus. Egg predation declined with increasing grassland cover around nests, whereas nestling predation declined with increasing nest concealment and nest height. Our results suggest that effective nest-site characteristics for avoiding nest predation differ during the incubation and nestling periods and are dependent on the predator species and their search strategies, at least in habitats with low predator species diversity.
... However, unbiased and sensitive assessment of diet content is difficult to achieve, largely due to the limited accuracy of many current methods. Such methods include (1) visual inspection of gut contents (Daniel 1973;Pierce & Boyle 1991), which presents bias against items are most easily degraded (for example, softbodied species), (2) stable isotope analysis (Major et al. 2007;Carreon-Martinez & Heath 2010), which yields only broad information on diet, such as whether diet items are terrestrial or marine (Hobson 1987;Basha et al. 2016), and (3) timelapse video (Dunlap & Pawlik 1996;Brown et al. 2008), for which species identification is difficult for small prey items or in low-light conditions. ...
... It should not be overlooked that cats can play an important role in rodent control (Engelhaupt, 2017;Fitzgerald et al., 1991;Kauhala et al., 2015;MacDonald, 2006). Rats and other rodents can have more negative impacts than cats on biodiversity loss, even in some islands (Bellard et al., 2016;Bergstrom et al., 2009;Brown et al., 1998;Courchamp et al., 1999;Doherty et al., 2016;Le Corre, 2008;Ozella et al., 2016;Rayner et al., 2007). For example, in some islands of New Zealand cats function as apex predators that minimize the impacts of invasive rats (Rayner et al., 2007). ...
Abstract Cats, Felis catus L. (Carnivora: Felidae), were domesticated because of their role in rodent control around human settlements. Free‐roaming cats (henceforth, referred to as “cats”) can predate on a wide variety of small‐ to medium‐sized animals and affect biodiversity. The impact of cats on biodiversity varies from country to country, region to region, and habitat to habitat. Depending on the location and context, the overall impact of cats on biodiversity can be negative, neutral, or positive. Management of cats should take into account the complex interactions that occur between cats, rodents, and the species they prey upon.
... Nest predation events can be difficult to identify as predators do not always leave signs or the signs are quickly concealed by bird activity (Brown et al. 1998), thus accounting for the high percentage of nests with unknown causes of failure. Conservation and management efforts to improve hatching success can be limited when a large proportion of nest failures are due to unknown causes. ...
Beach nesting waterbirds are among the most vulnerable groups of birds that are threatened by climate change, habitat loss, predation, and human disturbance. To improve conservation management strategies, causes of nest failure for ground-nesting waterbirds and effectiveness of mammalian predator control were investigated. Changes in breeding population size and hatching success of Royal (Thalasseus maximus) and Sandwich (T. sandvicensis) terns were evaluated based on pre-mammalian removal (2012-2014) vs. post-mammalian removal (2015-2016) breeding data. Video systems were used at colonies in 2015 and 2016 to determine causes of nest failure. No differences in breeding parameters were found between removal periods, however video data confirmed nest predation as the primary cause of nest failure. Laughing Gull (Leucophaeus atricilla) was the top predator and accounted for 63% of all detected predation events. In 2015, video monitoring identified a novel predator, exotic and invasive nutria (Myocastor coypus), that were responsible for 43% of predation events. In 2016, following a 280% increase in nutria removal from 2015, no nutria predation was recorded.
... Many New Zealand native birds are negatively affected by introduced mammalian predators (Holdaway 1989;Clout & Craig 1995;Brown et al. 1998;Innes et al. 2010;Robertson et al. 2012), in particular possums (Trichosurus vulpecula), ship rats (Rattus rattus) and stoats (Mustela erminea). Control of these mammals is the main tool used to conserve native forestdwelling birds in New Zealand (Parliamentary Commissioner for the Environment 2011). ...
... Introduced species can have cascading effects on entire ecosystems by changing the flow of energy and nutrients between trophic levels due to physical alterations of habitats (Simberloff 2008 (Raynor et al. 2013, Owen andPierce 2014, Pierce unpublished). Nest predation events can be difficult to identify as predators do not always leave signs or the signs are quickly covered up by bird activity (Brown et al. 1998), thus accounting for the high percentage of nests with unknown causes of failure. Conservation and management efforts to improve nest success are limited and difficult when a large proportion of nest failures are due to unknown causes. ...
Barrier islands in coastal Louisiana provide breeding habitat for numerous species of colonial nesting waterbirds. However, some of these islands are also inhabited by mammalian and avian species that have the potential to reduce overall waterbird breeding success, primarily through nest predation and disturbance. This study examines the effectiveness of mammalian control as a management tool for waterbird conservation and investigates specific causes of nest failure for ground-nesting colonial waterbirds using video monitoring. I evaluated changes in breeding population size, colony location, and hatching success of Sandwich Tern (Thalasseus sandvicensis), Royal Tern (Thalasseus maximus), and Black Skimmer (Rynchops niger) breeding on the Isles Dernieres Barrier Island Refuge(IDBIR)in response to mammalian control. Changes in breeding parameters were based on breeding data pre-mammalian removal (2012, 2013, and 2014) and compared to the same parameters post-mammalian removal (2015 and 2016). In addition, video systems were installed at Royal Tern, Sandwich Tern, and Black Skimmer colonies in 2015 and 2016 to determine specific causes of nest failure, and to determine the relative importance of each cause. The targeted mammalian species for removal in this study were coyote (Canis latrans) and raccoon (Procyon lotor), and invasive nutria (Myocastor coypus).Mammalian removal was conducted on the IDBIRin early spring of 2015 and 2016. East Raccoon Island was the only island where mammalian removal occurred in addition to the establishment of Royal Tern, Sandwich Tern, and Black Skimmer colonies. Nutria were the only mammal removed from East Raccoon Island; in 2015, an estimated 3.5 nutria/ha were removed, however in 2016 an estimated 9.8 nutria/ha were removed. I found no difference in breeding population size
or hatching success between pre-and post-mammalian removal study periods for Royal Terns, Sandwich Terns, or Black Skimmers. I did observe shifts in colony locations between pre-and post-mammalian removal periods for Royal and Sandwich terns, wherein the location with the largest colony in 2015 was abandoned in 2016, and colonies were newly established along dunes and sand fencing. Nest predation was the only cause of nest failure identified from video data of Royal Tern, Sandwich Tern, and Black Skimmer colonies, although predation was uncommon (N=1) at Black Skimmer colonies. In addition, video data revealed that nutria are the only mammalian predator of Royal and Sandwich tern nests on East Raccoon Island. In 2015, nutria were responsible for 42% of all predation events on video, however there was no evidence of nutria predation during the 2016 breeding season following the removal of 137 nutria. This is the first study to show nutria predation of bird eggs, and the extent to which nutria predation may influence breeding success. In addition, Laughing Gulls are the top nest predator and have the highest predatory influence in reducing hatching success. I conclude that waterbird breeding parameters on barrier islands are highly dynamic and can be influenced by a number of variables including nest predation and habitat characteristics. Mammalian removal on barrier islands can have important implications for waterbird conservation, and video monitoring is an essential tool to adequately assess the effectiveness of removal efforts.
... However, when a novel object like a camera (or other conspicuous marker) is placed near a nest, it can influence the behaviour of predators by either attracting them to the nest location (Reynolds, 1985;Renfrew and Ribic, 2003) or dissuading them (Herranz et al., 2002;Richardson et al., 2009). Cameras can also potentially affect incubation behaviour of the monitored birds in similar ways, and birds have abandoned their nests following placement of a camera (Brown et al., 1998;Renfrew and Ribic, 2003;Liebezeit, 2013). The value of cameras as a research tool is in part dependent on whether they effect changes in predator behaviours, reproductive success, or parental behaviour. ...
When monitoring the breeding ecology of birds, the causes and times of nest failure can be difficult to determine. Cameras placed near nests allow for accurate monitoring of nest fate, but their presence may increase the risk of predation by attracting predators, leading to biased results. The relative influence of cameras on nest predation risk may also depend on habitat because predator numbers or behaviour can change in response to the availability or accessibility of nests. We evaluated the impact of camera presence on the predation rate of artificial nests placed within mesic tundra habitats used by Arctic-breeding shorebirds. We deployed 94 artificial nests, half with cameras and half without, during the shorebird-nesting season of 2015 in the East Bay Migratory Bird Sanctuary, Nunavut. Artificial nests were distributed evenly across sedge meadow and supratidal habitats typically used by nesting shorebirds. We used the Cox proportional hazards model to assess differential nest survival in relation to camera presence, habitat type, placement date, and all potential interactions. Artificial nests with cameras did not experience higher predation risk than those without cameras. Predation risk of artificial nests was related to an interaction between habitat type and placement date. Nests deployed in sedge meadows and in supratidal habitats later in the season were subject to a higher risk of predation than those deployed in supratidal habitats early in the season. These differences in predation risk are likely driven by the foraging behaviour of Arctic fox (Vulpes lagopus), a species that accounted for 81% of observed predation events in this study. Arctic fox prey primarily on Arvicoline prey and goose eggs at this site and take shorebird nests opportunistically, perhaps more often later in the season when their preferred prey becomes scarcer. This study demonstrates that, at this site, cameras used for nest monitoring do not influence predation risk. Evaluating the impact of cameras on predation risk is critical prior to their use, as individual study areas may differ in terms of predator species and behaviour.
... In other studies nest predators have been identified at artificial nests (Reitsma et al. 1990, Leimgruber et al. 1994, Fenske-Crawford and Niemi 1997, but artificial nests may not provide the same cues to nest predators as real nests and therefore may attract a different suite of predators (Martin 1987, Willebrand andMarcström 1988). Only recently has the technology been available to identify predators at real nests with minimal intrusiveness (Brown et al. 1998, Thompson et al. 1999, Pietz and Granfors 2000. ...
Among hypotheses explaining nest-site selection, the potential-prey-site hypothesis predicts that birds place nests in areas with many potential nest sites, while the nest-concealment hypothesis predicts nest placement in sites with greater surrounding vegetation. We examined these hypotheses by comparing habitat attributes between Dusky Flycatcher (Empidonax oberholseri) nest sites and random sites, successful and unsuccessful nests, and nests depredated by birds versus mammals. Nesting success was 28% (n = 167), and predation was the most important cause of nest failure (96%) during the study (1998–2000) at our site in northeastern California. We identified 28 nest predators using surveillance cameras. Sciurid mammals were the most common predators (17 of 28, 61%), with Cooper's Hawks (Accipiter cooperii; 25%), small owls (11%), and Steller's Jays (Cyanocitta stelleri; 3%) accounting for the rest. Raptors preyed on nestlings more frequently than on eggs, while small mammals depredated nestlings and eggs in proportion to their availability. Dusky Flycatchers nested in larger shrub patches with greater shrub cover than at random sites, supporting the potential-prey-site hypothesis. Successful nests were in larger shrub patches surrounded by fewer seedlings and saplings compared to depredated nests, providing equivocal support for the potential-prey-site hypothesis. Nests depredated by birds were less concealed, located in smaller shrub patches, surrounded by fewer seedlings and saplings, and were closer to the shrub edge than nests depredated by mammals. Our results, strengthened by identification of nest predators, suggest that differences in search strategies among predators may constrain the ability of Dusky Flycatchers to optimize nest-site selection.
Depredadores de Nidos, Selección de Sitios de Anidación y Éxito de Anidación de Empidonax oberholseri en un Bosque Manejado de Pino Ponderosa
Resumen. Entre las hipótesis que explican la selección de sitios de anidación, la de “presa potencial” predice que las aves ubican sus nidos en lugares con muchos sitios de anidación, mientras que la de “ocultación del nido” predice la ubicación de nidos en sitios con mayor vegetación circundante. Nosotros examinamos estas hipótesis comparando características del hábitat entre sitios de anidación del mosquerito Empidonax oberholseri y sitios aleatorios, entre nidos exitosos y no exitosos, y entre nidos depredados por aves y por mamíferos. Entre 1998 y 2000 en un área del noreste de California, el éxito de anidación fue del 28% (n = 167) y la depredación fue la causa más importante del fracaso de los nidos (96%). Identificamos 28 depredadores de nidos utilizando cámaras. Los mamíferos sciúridos fueron los depredadores más comunes (17 de 28, 61%), mientras que los demás nidos fueron depredados por Accipter cooperii (25%), búhos pequeños (11%) y Cyanocitta stelleri (3%). Las aves rapaces se alimentaron con mayor frecuencia de pichones que de huevos, mientras que los mamíferos pequeños depredaron pichones y huevos en proporción a su disponibilidad. Los mosqueritos anidaron en parches con mayor cobertura de arbustos que sitios aleatorios, lo cual apoya la hipótesis de presa potencial. Los nidos exitosos se ubicaron en parches de arbustos más grandes rodeados por menos plántulas y renovales en comparación con los nidos depredados, lo que apoya equívocamente la hipótesis de presa potencial. Los nidos depredados por aves estuvieron menos ocultos, ubicados en parches de arbustos más pequeños, rodeados por menos plántulas y renovales, y estuvieron más cerca del borde del matorral que los nidos depredados por mamíferos. Nuestros resultados, fortalecidos por la identificación de los depredadores, sugieren que las diferencias en las estrategias de búsqueda entre depredadores pueden limitar la habilidad de los mosqueritos para optimizar la selección de sitios de anidación.
... Studying natural predation events is difficult because they are usually widely scattered in space and time (Pettingill 1976, Brown et al. 1998). In seabird colonies, however, multiple predation attempts may be observed in short periods of time ( Schauer andMurphy 1996, Whit- tam andLeonard 1999), thus making them ideal sites at which to observe the response of parents to nest predators under natural conditions. ...
Nest defense is a critical aspect of parental care that entails both costs and benefits. The purpose of this study was to examine patterns of nest defense in a colony of Arctic and Common Terns (Sterna paradisaea and S. hirundo, respectively) using observations of natural predators: Herring Gulls (Larus argentatus) and Great Black-backed Gulls (L. marinus). Tern nest-defense scores were higher for hunting gulls than for overflying gulls and for gull flights closer to the ground. Defense scores also were significantly higher during the chick stage than during the egg stage. Within the chick stage, response score initially increased with age, but then declined. The results of this study indicate that terns vary their defense in relation to characteristics of predators and offspring that influence the costs and benefits of defense.
... However, this finding may underestimate the impact of rats on bird populations. Rats are known to be egg and chick predators (Norman 1975;Clout et al. 1995;Brown 1997;Brown et al. 1998;Caut et al. 2008;Jones et al. 2008;Banks & Hughes 2012) and Sugihara (1997) suggested that rats are 'fastidious feeders that may consume egg contents without actually ingesting eggshells'. ...
... For both seasons, rats were responsible for most fantail nest predations outside Zealandia (14 / 26 predations) with ship rats the only invasive mammal observed on camera. The structure and lining of the concluded nest appeared undisturbed for all predation-unknown nests, and 6 of the 14 predation-rat nests, i.e., "Clean" (sensu Brown et al. 1998). Although no direct observation of predation upon adult fantails was made, an adult went missing from the breeding pair after 12 of 23 nest predation events. ...
Predation of indigenous birds by ship rats (Rattus rattus, [Muridae]) is an international conservation crisis and has been implicated in the decline of many endemic species. Effective management of threatened ecosystems relies on accurate assessments of invasive species impacts on native wildlife. To quantify the link between ship rat abundance and survival of small, endemic birds we investigated the prevalence of rat predation on nesting New Zealand Fantails (Rhipidura fuliginosa placabilis, [Rhipiduridae]), and its importance relative to other risk factors such as nest microsite. We surveyed 106 nests across forested reserves in Wellington City, New Zealand. Local abundance of ship rats was indexed using chew-cards placed around the nest and with tracking tunnels throughout reserves. We modeled the effects of ship rat abundance, weather, observer impact, and attributes of the nest for their influence on nest survival. Fantails were more likely to abandon nests located higher in trees and those built earlier in the breeding season. More nests failed when rat abundance was higher. Where ship rat abundance reached a 25% chew-card index (CCI), the probability of the nest surviving dropped below 50%, and for CCI above 45% only 20% of nests were predicted to survive. However, Fantails also exhibited a resilient strategy that improved survival because nests located on thinner branches were less likely to suffer predation. Our research suggests that nesting strategies of Fantails involve trade-offs and strategies that might protect them against one threat, might expose them to others. Fantails are a common endemic species and cope with moderate levels of nest predation, however conservation of small endemic birds with less resilient breeding strategies is likely to require management of ship rat populations to low levels.
... Nest survival was monitored by repeated observations of nest attempts at intervals of approximately 3 weeks. Predator sign at kea nests can be cryptic (Brown et al. 1998b), and kea may remove dead eggs and chicks (Jackson 1963), so that nothing is found at a failed nest attempt but an empty nest cavity. Consequently, distinguishing nest failure from early fledging becomes increasingly difficult as nestlings approach fledging age. ...
The kea (Nestor notabilis) and other New Zealand forest birds are threatened by predation by introduced mammals. Mammal control for biodiversity conservation in New Zealand commonly involves the aerial application of cereal-pellet baits containing sodium fluoroacetate (‘Compound 1080’), but its effectiveness for kea conservation has not previously been assessed. This study examined the effects of aerial 1080 on the reproductive success of kea in a lowland rimu forest on the West Coast of New Zealand’s South Island. We measured three parameters which collectively describe annual reproductive success (nesting frequency, nest survival and final chick count), within a Before-After-Control-Impact experiment. The Impact site was a 30 000 ha area over which 1080 baits were aerially applied in the spring of a rimu (Dacrydium cupressinum) mast year (i.e. with heavy seedfall), with the After phase of the experiment lasting for two kea nesting seasons. The invasive mammals ship rat (Rattus rattus), brushtail possum (Trichosurus vulpecula) and stoat (Mustela erminea), which are potential predators of kea nests, were much less abundant in the Impact site after 1080 application, on the basis of standard indexing techniques. There was strong statistical support for an effect of aerial 1080 on kea nest survival. Aerial 1080 improved the odds of daily nest survival by a factor of 9.1 at the treatment site. Nest survival rates in the Control and Impact sites, before the application of 1080, were 21% and 46.4%, respectively. After the application of 1080 to the Impact site, nest survival increased to 84.8% in this site, whereas it declined to 12.2% in the untreated Control site. This substantial positive effect of aerial 1080 on kea nest survival is attributed to the effective control of mammalian nest predators, particularly the secondary poisoning of stoats.
... Stable isotope analysis is imprecise, 52 yielding only broad information on diet such as relative consumption of protein and plant 53 matter, as well as information on whether prey items are terrestrial or marine in origin 54 (Hobson 1987;Basha et al. 2016). Time-lapse video (Brown et al. 2008) requires 55 identification of the specific prey item, often difficult or impossible for small prey items or 56 in low-light conditions. 57 Perhaps the most widely applied current molecular method is DNA metabarcoding. ...
Background
Using metagenomics to determine animal diet offers a new and promising alternative to current methods. Here we show that rapid and inexpensive diet quantification is possible through metagenomic sequencing with the portable Oxford Nanopore Technologies (ONT) MinION. Using an amplification-free approach, we profiled the stomach contents from wild-caught rats.
Results
We conservatively identified diet items from over 50 taxonomic orders, ranging across nine phyla that include plants, vertebrates, invertebrates, and fungi. This highlights the wide range of taxa that can be identified using this simple approach. We calibrate the accuracy of this method by comparing the characteristics of reads matching the ground-truth host genome (rat) to those matching diet items, and show that at the family-level, false positive taxon assignments are approximately 97.5% accurate. We also suggest a way to mitigate for database biases in metagenomic approaches. Finally, we implement a constrained ordination analysis and show that we can identify the sampling location of an individual rat within tens of kilometres based on diet content alone.
Conclusions
This work establishes proof-of-principle for long-read metagenomic methods in quantitative diet analysis. We show that diet content can be quantified even with limited expertise, using a simple, amplification free workflow and a relatively inexpensive and accessible next generation sequencing method. Continued increases in the accuracy and throughput of ONT sequencing, along with improved genomic databases, suggests that a metagenomic approach to quantification of animal diets will become an important method in the future.
... However, the theft of nest-material and other predation events are infrequently reported because they are rarely witnessed and generally occur over only a few seconds (Skutch 1966;Major & Gowing 1994). Snap-shot cameras and video monitoring have become widely used methods for monitoring nest-predation (e.g.Major 1991;Brown et al. 1998;Berry 2002; Fulton in press a). They are advantageous in that they can continuously monitor nests. ...
I describe nine predation, nest-predation and disturbance events: four by ants, four by the South-western Carpet Python Morelia spilota imbricata and one by the Bilby Macrotis lagotis. Predation by ants was more important on or near the ground, and Greenslade’s Meat Ant Iridomyrmex greensladei was responsible for three of the four events. The Carpet Python took Rainbow Bee-eater Merops ornatus nestlings from a burrow, and free-flying Australian Ringnecks Barnardius zonarius from the tree-canopy and from the ground. The Bilby dug out a Bee-eater’s burrow, which it either depredated or from which it caused the nestlings to fledge prematurely. All observations were made at Dryandra Woodland, a 27 000-ha remnant of woodland, with an almost full community of animals that have declined or disappeared from the surrounding wheatbelt, 160 km south-east of Perth, Western Australia. The context of each event is discussed in relation to the broader background of a 3-year community-wide study of Dryandra’s birds, which involved continuous monitoring throughout each breeding season.
... However, the theft of nest-material and other predation events are infrequently reported because they are rarely witnessed and generally occur over only a few seconds (Skutch 1966;Major & Gowing 1994). Snap-shot cameras and video monitoring have become widely used methods for monitoring nest-predation (e.g.Major 1991;Brown et al. 1998;Berry 2002; Fulton in press a). They are advantageous in that they can continuously monitor nests. ...
I describe 16 predation and other disturbance events including the predation of birds and reintroduced mammals, nest-predation and the theft of nest-material. The Grey Shrike-thrush Colluricincla harmonica was identified as an important nest-predator, being responsible for four nest-disturbance events. Nest-material was stolen from a variety of active nests, causing some of them to fail; observed thefts involved physical contact between Australian Magpies Gymnorhina tibicen and Yellow-plumed Honeyeaters Lichenostomus ornatus; and a Rufous Treecreeper Climacteris rufa broke the eggs and destroyed the nest of Willie Wagtails Rhipidura leucophrys. Wedge-tailed Eagles Aquila audax were detected preying on reintroduced Boodies Bettongia lesueur. All observations were made at Dryandra Woodland, a 27 000-ha remnant of woodland 160 km south-east of Perth, in south-Western Australia. This site retains an almost full community of animals that have declined or disappeared from the surrounding wheatbelt, and has large areas of old-growth woodland. The context of each event is discussed in relation to the broader background of a 3-year community-wide study of Dryandra’s birds, which involved continuous monitoring throughout each breeding season.
... Avian Conservation and Ecology -Écologie et conservation des oiseaux 2(2): 2 http://www.ace-eco.org/vol2/iss2/art2/ The main predators of the North Island robin are the native owl (Ninox novaeseelandie) from the interior of the forest and the Australasian harrier (Circus approximans) from the surrounding matrix (Baker-Gabb 1981, Brown et al. 1998. Whereas owls hunt within the forest patch, harriers prey upon robins when they are visible through the canopy or when individuals cross the matrix between fragments; harriers have been seen circling close to canopy openings to localize robin song transmitted from recorders (A. ...
Natal dispersal is an important component in bird population dynamics and can influence the persistence of local and metapopulations. We examined natal dispersal in the North Island robin (Petroica longipes), a sedentary bird species distributed in a fragmented forest habitat on Tiritiri Matangi Island, New Zealand. Earlier studies have shown that the only dispersal phase in this species takes place when juveniles leave their natal patch, and that juveniles who fail to find suitable habitat do not survive their first winter. These findings suggest that natal dispersal behavior in this species is important for population viability. We found that juveniles were highly affected by the fragmentation of the forest habitat, with patch occupancy being positively correlated with degree of connectivity of the landscape. Most juvenile movements (52.1%) were observed between patches that were separated by less than 20 m. Juvenile North Island robins were found in all forest habitat types, including young and open stands. This suggests that the juveniles are not dependent on old forest stands during their dispersal phase. Based on these findings, we suggest that management of this regionally-threatened species should focus not only on maintaining populations in occupied patches and increasing the habitat quality of these patches, but also on protecting existing forest patches acting as corridors and creating new forest habitat among patches. This would greatly increase the viability of the species' metapopulations by increasing dispersal success between both unoccupied patches and subpopulations. Additionally, increased connectivity between forest patches could also be expected to increase the probability of successful dispersal of other threatened native species, many of which are also sensitive to the high degree of fragmentation of their habitats.
... Rodents of the genus Rattus, including the black rat (Rattus rattus), are among the most widespread invasive genera and currently occupy >80% of the world's islands, with new introductions continuing to occur (Atkinson, 1985;Pitman et al., 2005;Towns et al., 2006). Black rats have been implicated in declines of numerous bird populations (Bell, 1978;Brown et al., 1998;Dilks et al., 2003), particularly on islands (Atkinson, 1989), and their introduction has directly resulted in extinctions of islandendemic birds, lizards, and small mammals (Atkinson, 1985;Towns et al., 2006). Despite their wide distribution and impacts, not only to biodiversity, but also to agricultural crops (Ahmed et al., 1987;Tobin et al., 1996;Pimentel et al., 2001;Elmouttie and Wilson, 2005), studies addressing such basic topics as postinvasion homerange size and habitat use have been limited to only a few specific geographic regions. ...
Black rats (Rattus rattus) are among the most ecologically destructive invasive vertebrates. On San Clemente Island (SCI) they depredate multiple endemic endangered species. Rat control has been part of the Department of the United States Navy's endangered species conservation programs on SCI since 1987, but no previous research into their ecology had been conducted. To improve understanding and management of black rats on SCI, from September 2011 to January 2012, we conducted a radiotelemetry study to estimate spatial use metrics for 20 rats. We found 95% kernel density estimates ranged from 0.14 to 6.45 ha (mean = 1.75 ha) with an average home-range size of 2.09 ha for males and 1.53 ha for females. We did not detect any effect of habitat type or time of day on spatial-use metrics. Home range overlap among sympatric individuals ranged from 3% to 73%, with 19 of 20 individuals (95%) overlapping two or more other rats wearing transmitters. Better understanding of black rat spatial ecology will allow for improved rat-control efforts to facilitate ESA-listed taxa conservation efforts on SCI.
... Traditionally, assessing nest survival rates has involved regular visits to active nests. Now, remotely operated video systems are widely available and can be used to monitor nests with minimal disturbance (In- nes et al. 1994, Pietz and Granfors 1996, Brown et al. 1998). We used videocameras at nests to (1) test whether regularly approaching nests resulted in increased visitation rates by predators; and (2) assess whether mammalian predators used human scent trails to locate nests. ...
We used videocameras to monitor 39 nests of the Banded Dotterel (Charadrius bicinctus), a ground-nesting plover endemic to New Zealand that suffers from predation by introduced mammals. To test whether monitoring nests increased the chances of nests being visited by predators, 22 of the video-monitored nests were approached on foot daily to simulate conventional monitoring and 17 unapproached nests were monitored using videocameras only. The proportions of approached nests (46%) and unapproached nests (41%) that were visited by predators did not differ significantly, nor was there any evidence that predators used human scent trails to locate nests. This study provides some evidence that monitoring Banded Dotterel nests by regularly checking them does not influence their risk of predation.
Control de Nidos y Visita de Depredadores a Nidos de Charadrius bicinctus
Resumen. Usamos cámaras de video para controlar 39 nidos de Charadrius bicinctus, un ave endémica de Nueva Zelandia que anida en el suelo y es depredada por mamíferos introducidos. Diariamente nos acercamos a pie a 22 de los nidos controlados con cámaras para simular el modo convencional de seguimiento, y controlamos 17 nidos usando sólo las cámaras y sin acercarnos a ellos con el fin de examinar si el control convencional de nidos incrementa la probabilidad de visita de depredadores. La proporción de nidos personalmente examinados (46%) y no examinados en persona (41%) que fueron visitados por depredadores no difirió significativamente, y no hubo evidencia que los depredadores usan rastros de olores humanos para localizar los nidos. Este estudio sugiere que controlar regularmente los nidos de Charadrius bicinctus no influencia su riesgo de depredación.
... Previously, egg remains left at bird nests after predation events had been classified without direct observation (Moors 1983). The advent of video recording of predators at nests has shown how unreliable egg remains have been and how frequently they have been misclassified (Major 1991; Brown et al. 1998; Lariviere 1999). Similarly, with bird remains, it is important to either obtain direct observations to be able to classifY the remaining physical evidence, or explicitly state the methods used to attribute the remains to a predator. ...
We examined the carcasses of 148 Black-fronted Terns Sterna albostriata found during the 1998-2000 breeding seasons on the Ohau River, South Island, New Zealand. Predation was the primary cause of mortality of adults, juveniles and chicks, resulting in 47% of all deaths. Video footage showd Feral Cats Felis catus wre responsible for 6% of all predator-caused deaths, and physical evidence at carcass remains linked cats to another 19% of predations. Further evidence suggested Norway Rats Rattus norvegicus and Stoats Mustela erminea were responsible for 51% and 6% of predator-caused deaths, respectively. The prey remains left by the different predator species are described. Other causes of mortality included starvation (4%), power lines (1%), road traffic (1%) and various natural causes of mortality (5%). Causes of mortality could not be assigned to 41% of Black-fronted Terns, but most of these were young chicks that died at the nest soon after hatching. We suggest that predators are potentially the main cause of population decline in black-fronted terns and that predator control targeting cats and Norway Rats during the breeding season should be trialled.
... However, some predators may not leave signs at the nest (other than removing the nest contents), and hence description of potential predator communities may be biased towards species that leave signs (reviewed in Pietz and Granfors 2000). More recently, camera systems have been used to capture the act of predation on film ( Brown et al. 1998, Thompson et al. 1999, Pietz and Granfors 2000, alleviating this potential bias. These and other studies caution that previous assignments of predator identity based on signs left at the nest may be erroneous (Larivière 1999). ...
We used small video cameras to film predators at nests of American Redstarts (Setophaga ruticilla). We filmed three predation events, all by accipitrine hawks, in which no signs of predation were left at nests. Hence, as suggested by other workers, predator identification based on signs left at nests is unreliable. In addition, predation rates may be under-estimated if accipiters or other predators take nestlings just prior to fledging without leaving signs. These incidents may be interpreted by field workers as nests where young fledged successfully.
... Less frequent physical inspection of nest contents were timed to provide information on clutch size, hatching success, chick survival and numbers of fledglings produced where possible. Some nests were monitored day and night using time-lapse infra-red (IR) video equipment (Brown et al. 1998), and video footage was viewed on a VHS video recorder to note timing and duration of nest activity. ...
The kaka (Nestor meridionalis) is an endemic parrot of New Zealand, and is nationally endangered. Conservation of the species is primarily dependent on intensive control of introduced mammalian nest predators, particularly stoats (Mustela erminea) and brushtail possums (Trichosurus vulpecula). Breeding was studied in 4 sites: Waipapa (1996-2002) and Whirinaki (1998-2002) in the North Island, and Rotoiti (1997-2002) and Eglinton (1998-2002) in the South Island. In total, 145 nests were found. The proportion of radio-tagged females that bred at a site in a given year varied from 0-100%, with most breeding occurring in years of mast-fruiting or seeding by key food tree species. Kaka nested mainly in trunk cavities of live canopy or emergent trees. Egg-laying occurred from Oct to Mar, but differed between years within sites by up to a month, and was usually 2 months later at the most southern site (Eglinton) than elsewhere. Mean egg length was 41.5 mm, mean maximum breadth was 31.5 mm, and fresh egg mass was 22.6 g or 5.65% of female body weight. Clutches consisted of 1-8 eggs, most being of 3, 4 or 5 eggs (mode = 5), and mean clutch size did not differ significantly between the sites. The female alone carried out incubation, with her mate feeding her 8-12 times a day. Overall, hatching success varied from 39-66% between sites, but it also varied between breeding seasons at each site, in part due to the level of control of introduced predatory mammals. Kaka nestlings were covered in white down at hatching, and left the nest when c. 70 days old. Even when 11-20 days old, they were left unattended at night for 20-70% of time and by day for 50-85% of time. Twice females were filmed aggressively attempting to evict stoats that had killed broods in their nest cavities. Breeding productivity (proportion of eggs that produced fledglings) in the 4 study sites varied from 19% at Whirinaki (no control of predatory mammals) to 53% at Eglinton (intense control of predatory mammals). The implications of the breeding biology of the kaka are discussed in relation to conservation management of the species.
... Damaged clay eggs were examined for incisor marks and other signs of predator identity (Boulton & Cassey 2006), under a binocular microscope. Damage to real eggs and nests was compared with literature descriptions of characteristic damage caused by various predator species (Brown et al. 1996a(Brown et al. , 1998Innes et al. 1996). ...
Predation at nests contributes importantly to current declines of New Zealand forest birds. We
monitored the survival of natural and artificial arboreal nests in small forest remnants south-west of Hamilton,
where ship rat (Rattus rattus) and possum (Trichosurus vulpecula) abundances were also being measured in
Summer 2008/09. Artificial cup nests (N = 77) were placed in replicated blocks with and without pest control,
in both December and January. Natural nests (N = 11, five bird species) were observed from 13 October to 23
December 2008 in a forest with no pest control. Digital video cameras identified ship rats, brushtail possums and
harrier hawks (Circus approximans) as predators of eggs and chicks. There was no difference between artificial
and natural nests in daily survival rates monitored in December in a block with no pest control, suggesting that
artificial nests are reasonable surrogates for natural nests. Bite marks on clay eggs, other diagnostic sign, and
DNA swabbed from real and clay eggs confirmed ship rats and possums were the major introduced predators
at artificial nests. Bite marks also confirmed that harriers contribute to nest failure. Removal of ship rats and
possums in December improved the 14-day probability of survival of artificial nests, from P = 0.63 (95% CI
0.45–0.77) in the non-treatment block to P = 0.88 (0.74–0.95) in the treatment blocks. In January, the 14-day
probability of survival in all three blocks was intermediate at 0.80 (0.69–0.87), and the variation between them
could not be explained by including pest control in the model. The abundance of ship rats apparently declined
even in the non-treatment block over this time, for unknown reasons. Our data from tawa (Beilschmiedia tawa)
forest remnants confirm that control of ship rats and possums alone is sufficient to improve nesting success of
small arboreal birds in North Island forests.
... Part of the problem may come from the difficulty of observing rat and mouse behaviour in the wild, as predation by rodents is elusive, often occurs at night and below ground, and leaves few signs in the field. While observing the interactions between rodents and some groups of birds at their nest-sites is possible using automated photographic or video equipment (Brown et al. 1998;Sanders and Maloney 2002), this type of approach remains costly and requires a sufficient sample size to quantify the effects of the different causes of mortality. As a consequence, the effects of rodents on insular wildlife have often been assessed indirectly (e.g. ...
Bird conservation is nowadays a strong driving force for prioritizing rodent eradications, but robust quantitative estimates of impacts are needed to ensure cost-effectiveness of management operations. Here, we reviewed the published literature to investigate on what methodological basis rodent effects on island bird communities have been evaluated for the past six decades. We then discuss the advantages and limitations of each category of methods for the detection and quantification of impacts, and end with some recommendations how to strengthen current approaches and extend our knowledge on the mechanisms of impacts. We identified 13 distinct methods used to evaluate rodent effects on birds. Impact studies (152 studies considered) emphasized seabirds (67%), black rats (63%) and the Pacific Ocean (57%). Rodent impacts were most commonly assessed by observing bird remains in nests or emptied nests (51%), analysing rodent diets (30%) and manipulating rodent densities (26%). Among the less frequently used methods were, for example, correlative analyses between bird and rodent distributions or abundances (17%), artificial nests studies (5%), behavioural studies of predatory capacities (5%) and theoretical modelling of bird demographic parameters (3%). Direct observations of rodent-bird interactions (19%) are still poorly considered despite their potential to reveal cryptic behaviours and shed light on the mechanisms of impacts. Rodent effects on birds were most often measured as a change or difference in bird breeding parameters (74% of studies), while estimates of bird population growth rates (4%) are lacking. Based on the outcomes of this literature review, we highlight the need for collecting unbiased population-level estimates of rodent impacts, which are essential prerequisites for predicting bird population growth scenarios and prioritizing their conservation needs. This could be achieved by a more systematic integration of long-term monitoring of bird populations into rodent management operations and modelling bird population dynamics. We also strongly recommend including various complementary methods in impact assessment strategies to unravel complex interactions between rodents and birds and avoid faulty evidence. Finally, more research should be devoted to a better understanding of the cases of non-impacts (i.e. long-term coexistence) and those impacts mediated by mechanisms other than predation and ecosystem-level processes.
This manuscript was presented at the 5th International Conference of Rodent Biology and Management, held in Zhengzhou on 25-29 August 2014
Both first authors contributed equally
... Hedgehogs (Erinaceus europaeus), rats (Rattus spp.), and mice (Mus musculus) are known to frequently consume invertebrates (Taylor and Thomas 1993, Moss and Sanders 2001, Ruscoe 2001, Towns and Broome 2003, Jones et al. 2005. These mammals also consume plant material (Moss and Sanders 2001, Ruscoe 2001, Towns and Broome 2003, with rats also readily predating upon birds (Brown et al. 2008). Another species in the Hadramphus genus, H. stilbocarpae, experienced marked declines in population size due to rats (Taylor andThomas 1993, Towns 2009) indicating rats as a very likely predator of H. tuberculatus. ...
Burkes Pass Scenic Reserve, Mackenzie Basin, New Zealand is home to the only known
population of the critically endangered Canterbury knobbled weevil, Hadramphus tuberculatus.
Major threats to the weevil include introduced predators and habitat loss through weed
invasion, herbivores and fire. This report investigates the stomach contents of predators
trapped in a 185 hectare perimeter around the reserve. Trapping was conducted by
Environment Canterbury from December 2010 to April 2011. The stomachs of hedgehogs,
ferrets, feral cats and stoats were analysed and contents were recorded. Hedgehogs consumed
the highest amount of invertebrates, present in 20%, and ferrets were the most abundant
predator caught; however, no evidence of H. tuberculatus was found in any predator stomachs.
We suggest predator trapping continue as part of future management of the reserve to protect
not only the endangered weevil species but also other fauna including the recently identified
and possibly rare invertebrates and the endemic skink found there.
... There were also seasonal changes in rat and mustelid tracking that suggested mustelids might be controlling rats (Parker 2013), the main prey of stoats. Due to their arboreal foraging behaviour ship rats are likely to be the key predator of robin nests (Brown et al. 1998). Until further monitoring is carried out, it can only be speculated that predator numbers and nesting success are likely to vary across years and across sites. ...
The majority of New Zealand’s native forest bird species are currently limited by introduced mammalian species, and 24% of all terrestrial bird species are ranked as threatened. While there have been some spectacular achievements in the recovery of some of the most critically endangered bird species, many forest birds continue to decline. Without intervention, many of these species are on the pathway to extinction. In this thesis I used the South Island robin (Petroica australis) as a model to investigate aspects of two important management practices to protect native birds from introduced predators: (a) translocation of native birds to sanctuaries and (b) sustained control of introduced predators.
(a) I examined the demographic and environmental drivers for the successful establishment of translocated SI robins in a fenced mainland sanctuary (Orokonui Ecosanctuary, Dunedin) where introduced predators have been eradicated. One of the main causes for reintroduction failures is philopatric post-release dispersal from the area. I tested my hypothesis that pre-dispersal robin fledglings are less likely to return to their capture sites than older birds: Robins from two different age classes, post-natal dispersal juveniles (≥ 3 month than fledging) (n=25) and pre-natal dispersal fledglings (≤2 month since fledging) (n=20), were translocated during the 09/10 and 10/11 breeding seasons, respectively. Almost a third (32%) of the post-natal dispersal juveniles returned back to their site of origin but none of the pre-natal dispersal fledglings did. The retention rate for post-natal dispersal juveniles was only 24%, while 70% of the pre-natal dispersal fledglings settled in the release area. The results indicate that choosing fledglings drastically increases the likelihood to establish a persistent founder population. In addition, I fitted all robins released in 10/11 with radio transmitters and monitored their survival and movements for six weeks. The key findings of this telemetry study were: (1) movement activity was highest immediately after release, accompanied with higher mortality, and decreased over time; (2) birds went through two distinct phases: the exploratory and establishment phase, but settlement patterns were irregular and differed from individual to individual; and (3) dispersal distances were not affected by sex, source population or release site, but there was some indication that conspecific attraction, in form of encountering suitable breeding partners, may influence the post-release dispersal and settlement patterns of translocated robins.
(b) I investigated the effects on an established robin population of conventional pest control operation using aerially applied cereal bait containing the pesticide 1080 in exotic plantation forest in Silver Peaks, Dunedin. Monitoring of robin nest predators, using chew-tracking-card devices, following the pest control operation showed a significant reduction of rat and possum numbers to undetectable levels for at least three months, while in the non-treatment Silverstream area, pest numbers remained high throughout the study. All individually colour-banded robins monitored in treatment (n = 19) and non-treatment (n = 15) study areas were re-sighted, indicating that no birds died as a result of the poison drop. Nesting success, measured as Daily Survival Rate (DSR), in the treatment area was significantly higher than in the non-treatment area, but was not significantly different to the previous breeding season. My study showed that the 1080 operation had no direct adverse effect on the robin population in the Silver Peaks while reducing potential nest predators to extremely low levels.
The results from this thesis contribute directly to the conservation management of South Island robins - and potentially other native territorial passerines in New Zealand, and internationally where similar conservation strategies are used. The advancements in knowledge will directly contribute to improving the success rate of conservation efforts such as translocation and predator control, and emphasise the benefits of post-release monitoring and adaptive management.
... If this strategy is a primary anti-predator strategy, it could explain the large size and conspicuousness of LG nests, which are not concealed in vegetation. Some investigators consider that marks on artificial eggs are unreliable indicators of nest predator identity (Major 1991; Major et al. 1994, Brown et al. 1998, Fulton & Ford 2003), but in our study, predator markings on artificial eggs were consistent with our observations of actual nest predation. Nest predation experiments using real or artificial eggs may change (elevate or decrease) nest predation rates because the di#ering odours of the eggs may attract or discourage predation by small mammals (e.g., Rangen et al. 2000). ...
抄録
オーストラリア北部の熱帯地域の海岸に広がるマングローブ林では，巣への捕食圧が高いことが知られている。この地域には，2種のセンニョムシクイ類（ハシブトセンニョムシクイGerygone magnirostris とマングローブセンニョムシクイ G. levigaster）が同所的に生息している。ハシブトセンニョムシクイは主に，暗く生い茂ったマングローブ林内に潮汐によって生じる小川(tidal creek)の周辺に営巣し，マングローブセンニョムシクイはマングローブ林縁の干潟(salt flat)に点在する薮や孤立木に営巣する。近縁な両種は，ともにドーム型の巣を造るが，巣の大きさや色彩，形態が大きく異なる。このような営巣環境の違いと巣の外観の違いは，両種の巣への捕食と関連があるかもしれない 。そこで我々は人工巣を用いて，両種の巣の外観が捕食を避けるために，営巣環境に適応しているのかどうかを検証した。また，捕食者の特定も行なった。本実験より，マングローブセンニョムシクイの人工巣への捕食圧は，主たる営巣場所(salt flat)では，それ以外の営巣場所よりも低い傾向がみられた。一方，ハシブトセンニョムシクイでは営巣環境と捕食率の関連性ははっきりしなかった。これらの結果から，マングローブセンニョムシクイの巣は，主な営巣環境で捕食者の回避において適応的である可能性がある。また，捕食者を1例（キミドリコウライウグイス Oriolus flavocinctus）特定した。
... They eat vegetation, seeds, fungi, invertebrates, lizards, small birds, and the chicks or eggs of larger birds (Innes 2005). Ship rats are probably the most frequent predators at nests of North Island kokako (Callaeas cinerea wilsoni; Innes et al. 1999), kereru (Hemiphaga novaeseelandiae; Clout et al. 1995), and New Zealand robins (Petroica australis) and tomtits (Petroica macrocephala; Brown et al. 1993). North Island kokako are particularly vulnerable to ship rat depredation (Norbury et al. 2015); nest failure may be as high as 83% where populations of rats and other predators are not controlled . ...
... only macaques would totally rip apart a nest and leave material strewn over a wide area. Signs can be confused by parents or other predators visiting the nest after the original predation (Brown et al,, 1998). ...
... The majority of studies did not find any significant effect of nest cameras on daily survival rates (e.g. Brown et al. 1998;Staller et al. 2005). Although this may sometimes be due to small sample size and lack of statistical power rather than the lack of any effect, some robust studies sizes have found no difference in survival between nests with and without cameras (e.g. ...
Executive summary This report presents results from work conducted by the University of East Anglia and British Trust for Ornithology, under contract to Breckland District Council and with the support of the Forestry Commission. The breeding success of nightjar and woodlark, the abundance and distribution of fox and carrion crow, and the levels of recreational activity, were studied in 2008 and 2009 within the Breckland Forest SSSI, part of the Breckland SPA. A large and robust sample size was achieved for woodlark nests, visitor survey points and crow and fox counts. A smaller but informative sample size was achieved for nightjar nests. There was no relationship between levels of fox or crow activity, and levels of recreational activity, or proximity to carpark, or amount of urban settlement in surrounding buffers. Thus recreational activity and development are unlikely to increase the activity of these potential predator species. Monitoring of nests by miniature digital nest cameras showed that woodlark are exposed to a wide range of nest predators, including fox, kestrel, adder, hedgehog and stoat, and minor contributions from an additional seven species that included domestic cat and domestic dog. Analysis of a large sample of nests (147 nests providing 781 egg days and 1144 chick days) provided strong evidence that neither woodlark nests success, nor the productivity of successful nests, were affected by the levels of recreational activity observed within this study. Analysis of broods from 54 successful nests gave no evidence that recreational activity affected post-fledging survival. Nightjar nests were only predated by mammalian predators, primarily fox and badger, with no predation by crow or any other diurnal avian predator over the 13 predation events where the predator was identified. There was no evidence that rates of flushing of incubating female nightjar were higher close to paths, nightjar did not nest further from paths in patches with greater levels of recreational activity, and no instances of flushing by dogs were observed in over 2000 hours of diurnal footage from 22 nests. Thus overall, no support was found for the hypothesis that recreational disturbance exposes nightjar nests to predation by crows when females are flushed by dogs, at least in this landscape at the current rates of recreational activity. Analysis of a useful sample of nests (44 nests, providing 297 egg days, 430 chick days and a total of 522 nest days) produced no evidence for any effect of recreational activity on nightjar nest success; conversely strong evidence for a nil effect is presented.
... Identification of predators that influence prey populations often relies on inference and educated guessing. Nest remains, tracks, and other traditional techniques (Moore 1983, Martin 1987, Lyver 2000 are not definitive evidence for associating specific predators with acts of predation (Major 1991, Major and Gowing 1994, Brown et al. 1998Thompson et al. 1999, Sanders and Maloney 2002, Peterson et al. 2004. Predators active at night are especially difficult to identify because they are more difficult to observe than diurnal species and consequently the contribution of nocturnal predators to the total predation effect is unknown. ...
... Blackbirds, chaffinches and tomtits tend to feed on or close to the ground (O'Donnell & Dilks 1994) so may be more vulnerable to predation compared with the other species monitored (e.g. Brown et al. 1998). It is also possible that factors such as competition influence the persistence of species when overall bird numbers increase (Innes et al. 2010). ...
The control of introduced mammalian predators has become a standard response to protecting the viability of threatened wildlife species on oceanic islands. However, examples of successful outcomes of integrated pest control in forests are few. We investigated the efficacy of a pest control programme in the Landsborough Valley, New Zealand, during 1998−2009, which used continuous trapping to control mustelids and pulsed aerial application of the toxin 1080 to control rats (Rattus spp.) and brushtail possums (Trichosurus vulpecula). We predicted recovery in the populations of mohua (Mohoua ochrocephala) and other predator-sensitive hole-nesting birds and maintenance of numbers of South Island kaka (Nestor meridionalis meridionalis). In addition, we examined whether annual mean counts of mohua and kaka, as potential 'population indicator species', could predict those of other forest bird species. Annual counts of nine species (eight indigenous: bellbird Anthornis melanura, brown creeper Mohoua novaeseelandiae, fantail Rhipidura fuliginosa, grey warbler Gerygone igata, mohua, rifleman Acanthisitta chloris, tui Prosthemadera novaeseelandiae and yellow-crowned parakeet Cyanoramphus auriceps; one introduced: song thrush Turdus philomelos) showed significant increases during the 12-year study period. South Island kaka and redpoll (Carduelis flammea) showed no change with time. In general, trends in the two focal threatened taxa (mohua and kaka) were poor predictors of trends in other bird species. Lack of correlation in annual counts between bird species that share a recovery trajectory are likely due to differences in breeding biology and resource use. Our results suggest that an integrated strategy for predator management is effective at mitigating the impacts of predation by introduced mammals on forest birds, including the most vulnerable species, at a landscape scale.
... However, in a previous study nesting success was relatively low at both Silver Peaks and Silverstream (between 2007 and 2009) when, on the basis of results from ink footprint tunnels, rats were relatively abundant at both sites in 2009/10 (Parker 2013). Owing to their arboreal foraging behaviour ship rats, together with possums, are likely to be key predators of robin nests (Brown 1997;Brown et al. 1998). The high nesting success rate and relatively low rat numbers that we recorded before the poison drop at Silver Peaks may have been unusual, but until further monitoring is done, we can only speculate that predator numbers and nesting success are likely to vary across years and across sites. ...
New Zealand robins are thought to be vulnerable to poisoning by sodium fluoroacetate (1080), because individual birds found dead after aerial pest control operations have tested positive for 1080. We investigated the impacts of an aerial 1080 operation (preceded by non-toxic prefeeding) to control brushtail possums (Trichosurus
vulpecula) on the survival and breeding success of a robin population at Silver Peaks, Dunedin environs, South Island, New Zealand. We monitored the survival of individual marked robins and their nesting success before and after the 1080 application. Robins were also monitored at a non-treatment site at nearby Silverstream. The possum control operation at Silver Peaks reduced rats (Rattus rattus), possums and mice (Mus musculus) to very low numbers, which remained low for at least 3 months. In contrast, at Silverstream, pest numbers remained high throughout the study. All individually colour-banded robins monitored in the treatment area (n= 19) plus five unbanded territorial birds were resighted post-drop, indicating that no known birds died as a direct result of the poison application. Nesting success in the treatment area, measured as daily survival rate, was higher than in the non-treatment area, and did not significantly differ between the breeding seasons before and after the poison drop. Our study showed that the 1080 operation did not adversely affect the robin population at Silver Peaks, but did reduce important nest predators (rats and possums) to low levels. Although there was no evidence of a positive indirect impact on nesting success through the reduction in predators, rat and possum abundances were relatively low at Silver Peaks (cf. Silverstream) prior to the 1080 drop, and vary from year to year. We recommend continued monitoring over several seasons to ascertain whether 1080 operations have any long-term benefits for robins at Silver Peaks.
... Precautionary measures were taken to minimise human-induced mortality during nest monitoring, following Martin and Geupel (1993). Where nests failed, details were noted of the appearance of the nest and any remains of eggs or chicks to establish the cause of failure and identify potential predators (using information in Moors 1983, Major 1991, Pasitschniak-Arts and Messier 1995, Brown et al. 1998). Botha's Lark nests were found incidentally and their outcomes monitored in the same way as for Rudd's Lark nests. ...
Habitat use and breeding ecology of the threatened and poorly known Rudd's Lark Heteromirafra ruddi were studied in south-eastern Mpumalanga, South Africa, from October 2002 to April 2004. Data were also collected incidentally on the equally poorly known Botha's Lark Spizocorys fringillaris. Rudd's Larks establishing territories at the start of the summer breeding season selected grassland of lower than average height. Although grass in these territories had reached average height by the late breeding season, grassland selected by birds could still be distinguished from unoccupied grassland using a combination of other habitat variables. Botha's Lark was encountered less frequently than Rudd's Lark, but was always encountered along transects that also held Rudd's Lark, indicating a degree of overlap in habitat selection. However, the two species appeared to differ in nest site selection; Rudd's Lark nests were most frequently built in unburned grass and Botha's Lark nests on recently burned land. First egg dates of 93 Rudd's Lark nests ranged from late October to late March, with peak laying in January and February. Most clutches were of three eggs, and both incubation and nesting periods appear long for a lark, at 13–14 d and 13 d, respectively, for both species. Average nesting success, estimated using an extension of the Mayfield method, was around 30%, but showed a significant decline as the breeding season progressed and was lowest during the peak nesting period. Clutch size was significantly smaller in Botha's Lark (median = 2) and nesting took place significantly earlier, largely on land recently burned. Botha's Larks largely abandoned the study area after a short and possibly curtailed breeding season. Predation was the main cause of nest loss in both species and examination of the remains of dummy eggs identified mongooses, rodents and snakes as the main predators. Late burning of grassland might shorten the potential breeding season of Rudd's Lark and lead to a peak of nesting that coincides with high predator numbers. The earlier nesting of Botha's Lark suggests that this species may have been even more severely affected by a shortening of the breeding season. A model of Rudd's Lark potential distribution confirms previous suggestions that there might be a population of the species in the north-eastern Free State and identifies possible new sites elsewhere.
... Rats have been video recorded predating and scavenging on eggs and juvenile native bird species (K. P. Brown, Moller, Innes, & Jansen, 2008). Rat invasion to remote islands of New Zealand's archipelago have subsequently resulted in the annihilation of native floral and faunal populations including bird, bat and invertebrate species. ...
The Punakaiki Coastal Restoration Project (PCRP) was established to restore sand plain forest to a landsape that had been previously mined and farmed. Over 100,000 trees have been planted to date. The site is adjacent to the Nikau Scenic Reserve which is highly ecologically significant, and it is in the flight path of a unique Westland black petrel colony. Research investigating the potential indicators of ecological restoration success at the PCRP was undertaken over two years. This 12-month research report adds to a baseline survey of the site completed in 2012.
... data). Further direct evidence for predation was recorded for Broad-billed Prions in the current study, where both eggs and chicks of birds breeding in caves (where mice are abundant; Cuthbert et al. 2011) were found with injuries consistent with mouse predation (Brown et al. 1998;Cuthbert and Hilton 2004). While breeding success of many seabirds can be highly variable, often in response to at-sea conditions (Warham 1990), we consider it very unlikely that environmental conditions would be responsible for consistently low breeding success and low burrow occupancy across four different species and over several years of monitoring. ...
The predatory behaviour of introduced house mice Mus musculus at Gough Island is known to impact on albatross and petrels, resulting in the Tristan Albatross Diomedea dabbenena and Atlantic Petrel Pterodroma incerta being listed as “Critically Endangered” and “Endangered”, respectively. Although predation has been documented for two burrowing petrels and one albatross species, the impact of house mice on other burrowing petrels on Gough Island is unknown. We report burrow occupancy and breeding success of Atlantic Petrels, Soft-plumaged Petrels Pterodroma mollis, Broad-billed Prions Pachyptila vittata, Grey Petrels Procellaria cinerea and Great Shearwaters Puffinus gravis. With the exception of the Great Shearwater, breeding parameters of burrowing petrels at Gough Island were very poor, with low burrow occupancy (range 4–42%) and low breeding success (0–44%) for four species, and high rates of chick mortality in Atlantic Petrel burrows. Breeding success decreased with mass, suggesting that smaller species are hardest hit, and winter-breeding species had lower breeding success than summer breeders. The results indicate that introduced house mice are having a detrimental impact on a wider range of species than previously recorded and are likely to be causing population declines among most burrowing petrels on Gough Island. The very low values of burrow occupancy recorded for Soft-plumaged Petrels and Broad-billed Prions and greatly reduced abundance of burrowing petrels in comparison to earlier decades indicate that Gough Island’s formerly abundant petrel populations are greatly threatened by the impact of predatory house mice which can only be halted by the eradication of this species from the island.
... Because the landbird community on Corvo is species-poor (seven species), we used the total number of all species, seen or heard, during a survey as an index of landbird abundance. Landbirds are more conspicuous during their breeding season and this behaviour increases both the likelihood of detection and predation by cats (Brown et al., 1998). To reduce confounding abundance with increasing detectability due to singing behaviour, we counted only birds that were detected by their contact or alarm calls in each season. ...
Populations of feral (not owned by humans) and domestic cats Felis catus coexist in most inhabited islands, and they have similar impacts on native species. Feral cats are generally believed to vary their diet according to prey availability; however, no previous studies of diet have tested this hypothesis on insular ecosystems with a limited range of available prey. Because domestic cats kill prey independently of hunger, the spatial extent of their impact on wildlife will be influenced by home-range size. In this study, we combined dietary information with cat movements to assess the impacts of feral and domestic cats on island biodiversity. We quantified the diet of cats from scat samples collected across one year and tested whether diet varies by season. The abundance of main prey categories was also estimated to document seasonal variation in prey availability for cats. Finally, we tracked domestic cats by global positioning system units in all four seasons to examine whether home-range patterns varied seasonally. The diet of cats constituted three prey groups (rodents, birds and invertebrates), and the seasonal variation in consumption of each taxon matched the seasonal variation in prey availability, thus supporting the generalist behaviour of cats on oceanic islands. Roaming behaviour varied among individuals and across seasons, but could not be explained by availability of prey. Unconfined cats had larger home-ranges than confined cats, but most domestic cats strayed <1 km from home. Thus, confinement of domestic cats might reduce the spatial extent of cat impact on native prey populations on oceanic islands.
... At present, rats occupy 82% of archipelagos worldwide; most of them outside of their native ranges [14], where they are responsible for the decline and eventual elimination of many native animal species1920212223. These impacts may arise through direct predation [24], inter-specific competition [25] or indirect effects [26]. In particular, the decline of seabird populations on islands is often triggered by rat invasions [14,18]. ...
... At present, rats occupy 82% of archipelagos worldwide; most of them outside of their native ranges [14], where they are responsible for the decline and eventual elimination of many native animal species [19][20][21][22][23]. These impacts may arise through direct predation [24], inter-specific competition [25] or indirect effects [26]. In particular, the decline of seabird populations on islands is often triggered by rat invasions [14,18]. ...
Seabirds nesting on islands are threatened by invasive rodents, such as mice and rats, which may attack eggs, chicks and even adults. The low feasibility of rat eradications on many islands makes the development of alternate control plans necessary. We used a combination of field experiments on a Mediterranean island invaded by black rats (Rattusrattus) to evaluate (1) the predation risk posed to different-sized seabird eggs and (2), the potential of two deterrent methods (electronic and chemical) to reduce its impact. Rats were able to consume eggs of all sizes (12 to 68 g), but survival increased 13 times from the smallest to the largest eggs (which also had more resistant eggshells). Extrapolation to seabird eggs suggests that the smallest species (Hydrobatespelagicus) suffer the most severe predation risk, but even the largest (Larusmichahellis) could suffer >60% mortality. Nest attack was not reduced by the deterrents. However, chemical deterrence (conditioned taste aversion by lithium chloride) slowed the increase in predation rate over time, which resulted in a three-fold increase in egg survival to predation as compared to both control and electronic deterrence. At the end of the experimental period, this effect was confirmed by a treatment swap, which showed that conferred protection remains at least 15 days after cessation of the treatment. Results indicate that small seabird species are likely to suffer severe rates of nest predation by rats and that conditioned taste aversion, but not electronic repellents, may represent a suitable method to protect colonies when eradication or control is not feasible or cost-effective.
... Rat tracking rate was negatively correlated with robin establishment, indicating that improvements in predator control at release sites will benefit reintroduced populations. This finding was somewhat unexpected, because although ship rats are known to prey on nesting female robins (Brown, 1998), survival of adult males and non-breeding females in established populations is not markedly affected by rat densities (Armstrong et al., 2006;Parlato and Armstrong, 2012). Translocation-induced stress is probably responsible for the relationship found here, given that reintroduced individuals are subject to a number of stressors as part of the translocation process (Dickens et al., 2009;Teixeira et al., 2007) and are especially vulnerable to predation immediately after release into a new location (Letty et al., 2007). ...
Aim
Species interactions are assumed to be stronger closer to the equator. However, numerous studies provided conflicting results and considerable controversy exists concerning the latitudinal patterns in the intensity of biotic interactions. Thus, the question of whether biotic interactions are stronger near the equator remains open. Here, we provide a global evaluation of latitudinal trends in nest predation in songbirds and their explanations.
Location
Worldwide.
Taxon
Songbirds (Aves: Passeriformes).
Methods
We collected published data on nest predation in 1297 populations of 659 species across the globe (124,958 nests). We quantified latitudinal trends in the intensity of nest depredation (daily predation rate, DPR) and in potential demographic impacts of nest depredation (the proportion of nests destroyed by predators). We also quantified the latitudinal trend in the proportion of failed nests destroyed by predators and assessed how nest depredation and latitudinal trends differed across nest types. We aimed at explaining spatial variation in nest predation by productivity and species richness of potential nest predators.
Results
All measures of nest predation increased towards the equator and the increase was stronger in the northern hemisphere. Nest predation also increased with time, and it was higher in open nests than in cavities. Nest predation increased with productivity (indexed by NDVI), independently of latitude. It also increased with species richness of potential nest predators, but this effect was confounded with latitude.
Main conclusions
Tropical songbirds faced both higher intensity of nest predation (higher DPR) and more detrimental demographic outcomes of nest depredation (higher proportion of nests lost to predators). Moreover, the proportion of nest failure caused by predators also increased towards the equator. Our results support the view that birds are subject to strong biotic interactions close to the equator. Nest predation increased with productivity and tended to increase with species richness of potential nest predators.
Camera traps are being increasingly used in biological surveys. One of the most common uses of camera trap data is the generation of species inventories and estimations of species richness. Many authors have advocated for increased camera trap-nights (long deployment times or more cameras in an array) to detect rare or wide-ranging species. However, in practice, the number of traps and the duration of surveys are constrained; a survey leader must make decisions about allocating the available cameras to sites. Here we investigate the effect of deployment time, camera array size and number of sites on detection of saxicoline mammal and varanid species obtained from surveys of discrete vegetation pockets in tropical Australia. This paper provides an analysis method for optimising decisions about how a limited number of cameras should be deployed across sites. We found that increasing the number of sites leads to larger species richness estimates in a shorter period. Increasing the number of cameras per site also leads to higher species richness estimates in a shorter time, but not to the same extent as increasing the number of sites. With fewer sites used or smaller arrays deployed at each site, a longer deployment duration is required, especially for rarer or wider-ranging species, or those not attracted to bait. Finally, we compared estimates of species richness generated by our camera trapping to those generated by live trapping at a subset of our sites, and found camera traps generated much larger estimates.
Predation at nests contributes importantly to current declines of New Zealand forest birds. We monitored the survival of natural and artificial arboreal nests in small forest remnants southwest of Hamilton, where ship rat (Rattus rattus) and possum (Trichosurus vulpecula) abundances were also being measured in Summer 2008/09. Artificial cup nests (N = 77) were placed in replicated blocks with and without pest control, in both December and January. Natural nests (N = 11, five bird species) were observed from 13 October to 23 December 2008 in a forest with no pest control. Digital video cameras identified ship rats, brushtail possums and harrier hawks (Circus approximans) as predators of eggs and chicks. There was no difference between artificial and natural nests in daily survival rates monitored in December in a block with no pest control, suggesting that artificial nests are reasonable surrogates for natural nests. Bite marks on clay eggs, other diagnostic sign, and DNA swabbed from real and clay eggs confirmed ship rats and possums were the major introduced predators at artificial nests. Bite marks also confirmed that harriers contribute to nest failure. Removal of ship rats and possums in December improved the 14-day probability of survival of artificial nests, from P = 0.63 (95% CI 0.45–0.77) in the non-treatment block to P = 0.88 (0.74–0.95) in the treatment blocks. In January, the 14-day probability of survival in all three blocks was intermediate at 0.80 (0.69–0.87), and the variation between them could not be explained by including pest control in the model. The abundance of ship rats apparently declined even in the non-treatment block over this time, for unknown reasons. Our data from tawa (Beilschmiedia tawa) forest remnants confirm that control of ship rats and possums alone is sufficient to improve nesting success of small arboreal birds in North Island forests.
Predation of eggs and/or chicks is the main cause of nesting failure in birds. Nest predation has been studied in many habitats in New Zealand, but few studies have been conducted in urban ecosystems. Twenty-one nests of four bird species (blackbird [Turdus merula], song thrush [Turdus philomelos], fantail [Rhipidura fuliginosa], and silvereye [Zosterops lateralis]) were monitored over one breeding season in Hamilton using time-lapse recordings. Five predation events were filmed (two by cats [Felis catus], and three by ship rats [Rattus rattus]), 10 nests successfully fledged chicks and 6 nests failed owing to poor weather, desertion, or unknown events. Although the sample size was small, our data suggest that nesting success may be higher in urban Hamilton than in other unmanaged habitats where predation rates can exceed 80%. We recommend that future studies of nesting success in urban birds should also focus on the fates of fledglings, as anecdotal evidence suggested that predation rates may have been highest at this stage.
In urban landscapes, predators are often more abundant or diverse than in rural areas, but few studies have examined how the identity of actual nest predators varies with urbanization. From 2007 to 2010, we used time-lapsed video to record activity at nests of the Northern Cardinal (Cardinalis cardinalis), Acadian Flycatcher (Empidonax virescens), Gray Catbird (Dumetella carolinensis), and Wood Thrush (Hylocichla mustelina) in riparian forests in urban and rural landscapes of Ohio, and we examined the extent to which predator identity was predicted by landscape composition. In 99 records of depredation, we identified 21 species of nest predators (17 in rural, 15 in urban). No single species dominated, though the Brown-headed Cowbird (Molothrus ater; 18% of recorded depredations) and northern raccoon (Procyon lotor; 11%) were the most commonly recorded predators. Birds were responsible for 62% of depredations, followed by mammals (36%) and snakes (2%). By category of predator, mesopredators were the most likely to remove all nest contents, depredate nests at night, and concentrate on the nestling stage. Mesopredators also were most important in urban landscapes, accounting for 35% of urban but only 13% of rural depredations. Small birds (46%), including the cowbird, Common Grackle (Quiscalus quiscula), and House Wren (Troglodytes aedon), plus raptors (21%), were responsible for most rural depredations. The relative proportion of nests depredated by mesopredators increased as the landscape surrounding a forest urbanized. These data indicate that the composition of the actual predator community may not mirror patterns of abundance or diversity along the rural-to-urban gradient.
En paisajes urbanos, los depredadores son generalmente más abundantes o más diversos que en áreas rurales, pero pocos estudios han examinado como varia la identidad de los depredadores con la urbanización. Desde 2007 a 2010, utilizamos grabaciones de video para registrar la actividad en nidos de Cardinalis cardinalis, Empidonax virescens, Dumetella carolinensis y Hylocichla mustelina en bosques ribereños en paisajes rurales y urbanos de Ohio. También examinamos el grado al cual era posible predecir la identidad de los depredadores con base en la composición del paisaje. En 99 registros de depredación, identificamos 21 especies de depredadores de nidos (17 en la localidad rural y 15 en la urbana). Ninguna especie fue dominante, aunque Molothrus ater (18% de las depredaciones registradas) y Procyon lotor (11% de las depredaciones registradas) fueron los depredadores más comunes. Las aves fueron responsables del 62% de las depredaciones, seguidas por los mamíferos (36%) y las serpientes (2%). Por categoría de depredador, los de mediano porte fueron los que tuvieron mayor probabilidad de remover todo el contenido del nido, de depredar los nidos en la noche y de concentrar su actividad durante el periodo de pichones. Los depredadores de mediano porte también fueron los más importantes en el paisaje urbano, dando cuenta del 35% de las depredaciones urbanas pero sólo del 13% de las depredaciones rurales. Las aves pequeñas (46%), incluyendo a M. ater, Quiscalus quiscula y Troglodytes aedon, y las aves rapaces (21%) fueron las responsables de la mayoría de las depredaciones rurales. La proporción relativa de nidos depredados por depredadores de mediano porte fue aumentando a medida que el paisaje que rodeaba a los bosques se hacia más urbano. Estos datos indican que la composición de la comunidad de depredadores podría no estar reflejando los patrones de abundancia o diversidad a lo largo del gradiente rural–urbano.
Photo and video technology has become increasingly useful in the study of avian nesting ecology. However, researchers interested in using camera systems are often faced with insufficient information on the types and relative advantages of available technologies. We reviewed the literature for studies of nests that used cameras and summarized them based on study objective and the type of technology used. We also designed and tested two video systems that we used for three nest predator and behavioral studies. We found 327 studies that recorded 255 bird species spanning 19 orders. Cameras were most commonly used to study nest predators (n = 114), feeding ecology (n = 103), and adult behavior (n = 81). Most systems (69%) were partially or completely user-built. Systems that recorded in real time (≥25 frames per second), time-lapse(
In forest, birds were relatively more common than mammals as nest robbers than in farmland. Differences in the role of different predator species as nest robbers in forest vs. farmland habitats reflected their choice of habitat. No predator seemed to have developed specific nest-robbing skills. Loss of individual nests was considered as a random event. Predation rates were higher when nests could be detected from a distance. The main factor affecting the rate of predation in patchy environments is apparently the steepness of productivity gradients between an habitat island and the surrounding matrix rather than patch size itself. -from Author
We describe an electronic trigger coupled to an automatic camera for identifying predators at artificial nests. The system is portable, correctly exposes the predator during day or night for clear photographs, has close-up capabilities, automatic advance, and an external power supply for extended field use.
During 1980-84 I studied the fates of 821 artificial nests, 96 naturally occurring capercaillie (Tetrao urogallus) nests, and 12 black grouse (T. tetrix) nests at Varaldskogen, Norway. In 4 of the 5 years artificial nests with poor cover had higher loss rates than natural capercaillie nests. In 1981 natural capercaillie nests had a higher loss rate than artificial nests with poor cover. In 1981 the loss rate of natural capercaillie and black grouse nests increased as the season progressed, while the loss rate of artificial nests was constantly low. Capercaillie nests were probably detected by scent by predators most years, while predators oriented mainly by sight probably robbed most artificial nests. Loss of artificial nests was not an index to the loss of capercaillie nests. In artificial nests the losses depended on nest cover; however, natural capercaillie nests in poor cover had higher losses than nests in good cover only during 1 year.
In a park‐like area of 3.75 acres adjoining primary forest in Costa Rica, at an altitude of 2,500 ft., 83 nests, made by about 49 pairs of birds and two single females, were found in one year. Over a period of 20 years, 64 species were recorded as nesting in this same area.
The difficulties of learning the actual rate of success of nesting birds are discussed, and it is concluded that, in view of the impossibility of assessing the effects of visits of inspection to nests in natural habitats, statements of breeding success are at best rough approximations of what happens in the absence of an observer.
In the area of the census, nest‐success (the proportion of nests in which at least one egg was laid that produced at least one living fledgling) was 38–53% in four different years. During the four years 41 % of 208 nests were successful.
Of 756 nests of 23 species of altricial birds of the Central American lowlands that build open or roofed nests in clearings and second‐growth, 37% were successful. When the computation is restricted to nests found before the last egg was laid (class B nests), 35% of 434 nests were successful, and 30% of 883 eggs produced living fledglings.
In the neighbouring forests, nesting success was much lower, only 23.5% of 136 open or roofed nests producing at least one fledgling. Many forest birds increase their chances of success by entering neighbouring clearings to breed, but few open‐country birds build their nests in the forest.
In both forest and clearings, hole‐nesting birds in Central America are much more successful than open‐nesters, as has been found also in the North Temperate Zone.
A comparison of the results of a single season's observations in each of six Central American localities shows an increase of nesting success with altitude. In lowland Panama, the nest‐success was only 21%, in the Subtropical Zone of Costa Rica 53%, and in the altitudinal Temperate Zone of Guatemala 55%. The effect of altitude is complicated by differences in the amount of forest in the localities chosen for study, as well as by other factors difficult to assess.
In both the tropics and the North Temperate Zone, nest losses are substantially higher in woodland than in man‐made habitats, evidently because there are fewer predators in the latter; but, even in clearings in Central America, nesting success was considerably lower than it was found to be in numerous studies in the North Temperate Zone. The difference may, however, reflect the greater “wildness” of the localities where the writer's studies were made, rather than a true contrast between tropical and temperate zone conditions.
Snakes appear to be of the greatest single cause of nest losses in tropical America, but mammals, a few predatory birds, ants, and possibly even bats, destroy many eggs and young.
Since small broods and heavy predation permit only a small annual contribution to the adult population, it is evident that, in order to maintain the species, adults must enjoy fairly long lives. Recent statistical studies support this theoretical conclusion.
Prior to human settlement the endemic New Zealand avifauna evolved in the absence of mammalian predators. Subsequently mustelids, rodents and feral cats have become established and frequently prey on birds and nests. It has been suggested that, because of their evolutionary history, the endemic birds are especially susceptible to such predators. In this paper predation by mustelids and rodents on the eggs and nestlings of eight species of native bird is compared with that on five species of introduced European passerine inhabiting the same lowland forest.
Final outcomes were known for 101 nests of native birds and 48 nests of introduced birds found during three breeding seasons. There was no significant difference between the two groups in frequency of predation. Native birds lost 70-1% of their nests to predators and introduced birds 64-6%. Most predations occurred during the egg stage. Clutch size did not influence frequency of predation, but brood size did for Fantails and introduced birds. Stoats and weasels were responsible for 77-9% of predations on native birds and 77-4% on introduced birds; corresponding percentages for rodents (principally ship rats) were 14-7% and 19-4%. Mustelids destroyed proportionately more nests with chicks than with eggs, whereas rodents did the reverse. Predation on both groups of birds was not influenced by their nesting habitat, the species of tree used for nesting, or the height and position of the nest. The vulnerability to introduced predators of native New Zealand birds is discussed in relation to the historical declines of many species, and also their life-history patterns.
Identification of wildlife nest predators
- Rearden
Ecological factors effecting Wild Turkey nest predation on south Texas rangelands
- Baker B.W.