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Conservation of Island Birds.
Journal of Applied Ecology
... Island bird species have suffered the greatest rates of anthropogenic extinction in recent years, and constitute a disproportionately large number of currently threatened species (BirdLife International 2000). Their typically small populations and range sizes make them particularly vulnerable to habitat destruction, and they are frequently sensitive to introduced predators (Atkinson 1989 ). Fur-thermore, their restriction to one or more small, discrete sites makes them inherently vulnerable to catastrophic and stochastic events that can eliminate populations (Moors 1985, Whittaker 1998). Disentangling these combined threats, and assessing which are the most important, can be difficult. ...
... Thus, rat absence may not be a sufficient condition to allow populations of all species to persist. Island bird species most at risk from rat predation are smaller species and those without prior exposure to mammalian predators (Moors 1985). Falkland landbirds have evolved in isolation from mainland counterparts, hence they are almost all endemic subspecies or species. ...
A high proportion of island birds are threatened with extinction as a result of their vulnerability to introduced predators,
habitat destruction, and fragmentation/isolation effects. In order to conserve island species effectively, it is necessary
to disentangle these effects on distribution and abundance. We attempt to do this for the nine native passerines in the
Falkland (Malvinas) Islands, using a database of presence/absence on 59 offshore islands in the archipelago, linked to
data for each island on mammal presence, habitat modification, and isolation. Falklands native passerines are of
considerable conservation importance, comprising one endemic globally threatened species, several endemic subspecies,
and several restricted range species. Presence of rats on islands was by far the most important predictor of
passerine presence, overriding the effect of habitat modifications. The globally threatened endemic Cobb's Wren
Troglodytes
cobbi was absent from all islands containing rats. Some species were more likely, and others less likely
to occur on islands where tussac Poa
flabellata grassland had been destroyed by grazing. The former species were
primarily those adapted to dwarf-heath vegetation, and/or that thrive around human settlements. Island size and
isolation were important predictors of occurrence for several bird species. The analyses show that, if vegetation restoration
in the Falklands is to meet conservation aims, then it should be accompanied by introduced mammal control. Secondly,
they indicate that biogeographical effects on bird distribution among islands in the Falklands are important, and need
to be considered when assessing the conservation status of species, and when considering conservation action.
... Numerous Atlantic Forest protected areas are highly irreplaceable too, but again many of these are tiny (Parker & Goerck 1997) and the region does not stand out on a global scale map. Islands generally feature rather poorly, partly because of the tiny size of many islands, partly because islands are generally underrepresented in the global protected area system (Moors 1985). ...
... Two of the most important factors in the loss of island fauna are habitat destruction (loss or fragmentation ) and the artificial introduction of exotic or alien species (Moors 1985 ). One of the most destructive alien species is the ship rat or black rat, Rattus rattus, the world-wide success of which stems from its ability to disperse, its competitive superiority over similar species in disturbed or secondary habitats, and its ability to reproduce successfully in a wide variety of habitats (Clark 1980 ). Endemic in the Indian subcontinent, the ship rat spread to Britain with the Romans around 20 B.C. (Reumer 1986). ...
We radio‐tracked five male and four female rats for 6 nights in primary forest at Rotoehu, North Island. New Zealand. From trapping we estimated rat density at the study site to be 6.2 rats/ha. Radio‐tracking revealed mean (± SE) restricted polygon home ranges to be three times greater in males (1.1 ± 0.29 ha) than females (0.3 ± 0.04 ha). Male ranges overlapped considerably, whereas those of females were largely exclusive. The ranges of males encompassed several female ranges. Four radio‐collared rats were retrapped and administered a lethal dose of the anticoagulant poison brodifacoum. During the 3–5 nights after poisoning but before death, we detected no significant change in home range area or utilisation, arboreality, or movements. Further research is required to determine if rats prey on other fauna while fatally intoxicated or cause secondary poisoning after being eaten by other predator species.
... Cats Felis cattus and rats have led to or been implicated in many extinctions on islands (Moors 1985, Veitch 1985). Of the three mammalian predators present on Norfolk Island, the black rat Rattus rattus has the potential to be a significant threat to the owl. ...
The Norfolk Island Boobook Ninox novaeseelandiae undulata is confined to the small, isolated Norfolk Island group, an Australian territory. On morphological and biogeographical grounds, it is here classified as a large, distinctive subspecies of the New Zealand Morepork N. novaeseelandiae. In 1986 only one specimen, a female, survived. A shortage of large trees with suitable nesting holes appeared to be the immediate problem. The Australian Nature Conservation Agency, islanders and New Zealand wildlife authorities have cooperated in an attempt to re-establish an owl population in situ. Nest-boxes were erected in trees in the area frequented by the female and were used readily as roosts. In September 1987, two male New Zealand Moreporks were introduced. The female paired with one male and produced four hybrid F offspring (in 1989 and 1990). Two of these paired in mid-1991 and have since produced five F offspring (two in 1993 and three in 1994). The original female remains paired but now appears to be reproductively senile. At present there seems to be a shortage of mature males, since two female offspring are paired and both lay eggs and attempt to incubate them in the same nest; and a lone female has established a territory. In early 1995 all eleven owls appeared to be alive in the wild. The effort is low-cost, requires relatively little manpower, is carried out with minimal disturbance to the owls, and goes hand in hand with other conservation programmes.
... In addition, introduced mammals, like cats, dogs, rats Rattus spp. and Coatis Nasua nasua act as important nest predators of local avifauna (e.g. Moors 1985, Bourne et al. 1992, Hahn and Römer 2002). Although most Juan Fernandez bird species are endangered, few studies have researched their nesting requirements and little is known about the potential harmful effects of alien bird species and nest predators. ...
Understanding the particular nesting ecology of island endemic species represents the first step in
identifying suitable micro-habitats and establishing efficient management programmes. This could
become even more important when island bird assemblages are prone to invasion by ecologically
similar species that may eventually cause niche compression or the extirpation of species already
present on the island. In this study we describe the nesting ecology of both native and introduced
landbird species of the Juan Fernández Islands and determine the extent to which native species could
be negatively affected by alien competitors. A total of 119 nests belonging to the 11 resident landbird
species were analysed. Landbirds exhibited a wide range of nesting habitat preferences on the
different islands, covering different vegetation types, altitudes and ecosystems. By means of a cluster
analysis we determined that competition between alien and endemic species apparently does not
represent an important factor affecting resource use by endemic birds. Endemic landbirds preferred
sites comparatively higher above the ground, with a greater slope and a larger level of shelter, than
alien species. The introduced hummingbird, the Green-backed Firecrown Sephanoides sephaniodes,
had different nesting preferences to the endemic Juan Fernandez Firecrown S. fernandensis, whereas
the House Sparrow Passer domesticus selected nest sites located in populated areas, suggesting that
both alien species may not be competing with endemic passerines for nest sites. However, urgent
measures are necessary to reduce the potential predation risk on Juan Fernandez Firecrown nests by
the alien Austral Thrush Turdus falcklandii.
Results of a recent land bird population survey of the Juan Fernandez Archipelago are presented. To additionally gain indications for possible tendencies, two censuses with a seven year interval were carried out (1994/95and 2001/02). During the 111 line transect counts 2496 bird records were made, covering the eleven resident species and the three islands (Robinson Crusoe, Alejandro Selkirk, Santa Clara). On base of this total bird numbers were calculated, including additional data of distribution and ecology, for each island, habitat type, and species. For the entire archipelago (9¬380 ha) in 2001/02 a total of 15 175 land bird specimens is calculated (1.62 ind./ha). Non-endemics were more abundant than endemics (63:37%). Robinson Crusoe shows the highest overall land bird density (2.56 ind./ha), however, mainly basing on non-endemics (70%). Contrarily Alejandro Selkirk hosts much lower individual numbers (0.65/ha), but endemics take a higher proportion on the overall land bird community (65%). Three of the endemic taxa possess very low total population sizes: Falco sparverius fernandensis, Sephanoides fernandensis, and especially Aphrastura masafuerae with only about 140 individuals. Although differences between the two study periods generally may be related to natural fluctuations, the populations of the mentioned taxa probably have suffered strong decline since human impact began in 1574. Alteration of habitats, introduction of predators, and immigration of competitive birds seem to be the main threats for these endemics. Basing on these results, the archipelago represents not only the most important endemic bird area of Chile and in the south-east Pacific Ocean, but also the most threatened one including several endangered endemics. Conservation management should include monitoring of the bird populations, basic research of their ecology (especially reproduction), and removal of introduced (plant and animal) species. Eradication campaigns should start with goats on Alejandro Selkirk, rabbits on Santa Clara, and cats in Robinson Crusoe’s settlement.
We used the introduction of a generalist nest predator, the red squirrel Tamiasciurus hudsonicus, and of a large herbivore, the Sitka black-tailed deer Odocoileus hemionus sitkensis, to the islands of Haida Gwaii (Queen Charlotte Islands, British Columbia, Canada) to study how predator assemblage and habitat quality and structure influenced nest predation in forest birds. We compared losses of natural nests to predators on islands with and without squirrels. We selected nine islands with or without squirrel or deer and used 506 artificial nests put on the ground or in shrubs to further analyse variation of nest predation with predator assemblage and habitat quality for the predators. For both natural and artificial nests predation risk was higher in presence of squirrels. But predation risk varied within island categories. In presence of squirrels it was highest in stands with mature conifers where it fluctuated from year to year, in response to fluctuations in squirrel abundance. Vegetation cover around the nest had little effect on nest predation by squirrels. Where squirrels were absent, nest predation concentrated near predictable food sources for corvids, the main native predators, and increased with decreasing vegetation cover, suggesting that removal of the vegetation by deer increased the risk of predation by native avian nest predators that use visual cues. Predation risk in these forests therefore varies in space and time with predator composition and with quality of the habitat from the predators’ perspective. This temporal and spatial variation in predation risk should promote trade-offs in the response of birds to nest predation, rather than fine-tuned adaptations to a given predation pattern.
The Bristle-thighed Curlew Numenius tahitiensis is a rare shorebird that breeds in western Alaska and winters on oceanic islands in the tropical and subtropical Pacific Ocean. Before human colonization, the islands on which curlews winter were devoid of terrestrial predators, allowing curlews to evolve a rapid moult during which about 50% of adults become flightless. Especially when flightless, these birds are vulnerable to harvest by humans and to predation by introduced mammals such as dogs and cats. On atolls where they are harvested by humans, curlews tend to occur only on uninhabited islets. Consequently, human encroachment in Oceania has probably reduced Bristle-thighed Curlew numbers and altered winter distribution of the species. Future studies should (1) identify concentrations of wintering curlews, focusing in the Tuamotu Archipelago; (2) determine whether migratory stopover sites exist in the central Pacific between Hawaii and the southern end of the wintering grounds; and (3) establish a monitoring programme to assess population trends in several parts of the winter range. A comprehensive plan is needed to provide for the existence of predator-free islands throughout key portions of the winter range.
Obligately cooperative breeders (cooperators) display a negative growth rate once they fall below a minimum density. Constraints imposed by natural enemies, such as predators or competitors, may push cooperator groups closer to this threshold, thus increasing the risk that stochastic fluctuations will drive them below it. This may indirectly drive these groups to extinction, thereby increasing the risk of population extinction. In this paper, we construct mathematical models of the dynamics of groups of cooperators and non-cooperators in the presence of two types of enemies: enemies whose dynamics do not depend on the dynamics of their victim (e.g., amensal competitor, generalist predator) and those whose dynamics do. In the latter case, we distinguish positive (e.g., specialist predator) and negative (e.g., bilateral competitor) reciprocal effects. These models correspond to the classical amensal, predation and competition models, in the presence of an Allee effect. We then develop the models to study consequences at the population level. By comparing models with or without an Allee effect, we show that enemies decrease the group size of cooperators more than that of non-cooperators, and this increases their group extinction risk. We also demonstrate how an Allee effect at a lower dynamical level can have consequences at a higher level: inverse density dependence at the group level generated lower population sizes and higher risks of population extinction. Our results also suggest that demographic compensation can be achieved by cooperators through an increased intrinsic growth rate, or by decreasing the enemy constraint. Both of these types of compensation have been observed in empirical studies of cooperators.
Understanding patterns of differential extinction and predicting the relative risks of extinction among extant species are among the most important problems in conservation biology. Although recent studies reveal that behavior can be a critical component in many species’ extinctions or endangerments, current approaches to the problem of predicting extinction patterns largely ignore behavior. I reviewed how behavior can affect population persistence and then used recent avian extinctions and endangerments to illustrate behaviors relevant to extinction risk. Behaviors that affect population persistence can be grouped as aggregation, interspecific responses, dispersal, habitat selection, intraspecific behavior, and maladaptive behavior. Behavior that can affect extinction risk is not limited to birds; for example, in many taxonomic groups (vertebrate and invertebrate) there is evidence of socially facilitated reproduction in colonial species, Allee effects on reproductive success and survival, behavioral regulation of population size, and conspecific attraction to breeding sites. Incorporating specific behaviors into models predicting extinction probabilities and patterns should improve their predictions.
We found no protozoan parasites in 79 blood smears of birds from the Cook Islands, South Pacific. Our sample consisted of 55 smears from nine indigenous species of land and aquatic birds, and 24 smears from one introduced land bird The absence or scarcity of avian hematozoa in the Cook Islands is probably due to a very low prevalence of infection among introduced and naturally colonizing species of birds, rather than a scarcity of insect vectors. On one hand, the apparent absence or extreme scarcity of avian hematozoa, particularly the malaria‐causing Plasmodium spp., is fortunate from a conservation standpoint, considering the devastating impact that Plasmodium from human‐introduced mosquitoes and birds has had on the indigenous avifauna of Hawaii during the past century. On the other hand, our results suggest that the indigenous birds of the Cook Islands, much like those of Hawaii, would have little natural resistance to avian malaria should it be introduced. Thus precautions should be taken to prohibit the introduction of potentially infected nonnative birds or mosquitoes in the Cook Islands and elsewhere in Polynesia
Seabirds are chemical and physical engineers that are capable of transforming terrestrial vegetation by altering edaphic conditions,
generating physical disturbance, and affecting seed dispersal. Substantial changes in seabird populations are occurring worldwide
and are likely to have important consequences for plant community composition on islands and coastal areas. This review focuses
on the impact of seabirds on plant biomass, species richness and community composition. A total of 57 publications (42 studies)
were selected for review. Of the 42 studies represented in the publications, 55% were descriptive. Most studies took place
in Australia, New Zealand, the British Isles, Japan, North America, and sub-Antarctic islands. A few studies showed that aboveground
plant biomass in seabird colonies increased with sufficient rainfall and moderate temperatures. The majority of studies on
plant species richness showed a decrease in seabird colonies compared to areas unaffected by birds. However, species richness
was higher in areas of intermediate seabird disturbance, compared to undisturbed areas. Moreover, the effects of seabirds
on species richness varied with respect to island size. Most studies of plant community composition indicated that annuals,
ȁ8ruderals”, and cosmopolitan species increased in abundance in seabird colonies. Changes in plant communities in seabird
colonies appear to result mainly from altered soil nutrient concentrations and pH, increased physical disturbance, and seed
dispersal by seabirds and humans. However, few studies have rigorously studied the relative importance of these alterations.
Both the direction and magnitude of seabird effects are modified by: (1) density of birds, (2) temperature and precipitation,
and (3) proximity to human habitation. A reduction in seabird populations is likely to have negative consequences for native
plant species that rely on seabird disturbance for their persistence. However, seed dispersal by nesting seabirds, especially
gulls, frequently leads to invasion by cosmopolitan plant species and declines of native species. Further studies that incorporate
both quantitative sampling and manipulative experiments would go a long way in improving our understanding of how seabirds
affect plant communities.
The study of bones from archaeological sites in Eastern Polynesia has revealed much late Holocene extinction of birds. Because this extinction has been found in all Eastern Polynesian archipelagos where bird bones are part of the archaeological record (Marquesas, Society, Pitcairn, and Cook island groups), similar levels of extinction are likely to be found in other Eastern Polynesian island groups (Line, Tuamotu, Gambier, Austral, Easter), if the evidence is sought. Human impact is the most plausible explanation for these extinctions, which begin immediately after peopling of the islands about 2000 years ago and diminish only after the avifaunas are largely depleted.
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