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Large scale stoat control to protect mohua (Mohoua ochrocephala) and kaka (Nestor meridionalis) in the Eglinton Valley, Fiordland, New Zealand
Abstract
To enhance the breeding success and survival of kaka (Nestor meridionalis) and mohua (Mohoua ochrocephala), we initiated stoat (Mustela erminea) control in the Eglinton Valley (13 000 ha), Fiordland, New Zealand using a single 40 km line of traps spaced 200 m apart with traps set continuously. This low intensity stoat control regime permitted successful kaka breeding and fledgling survival was high. A large irruption of rats, probably due to two consecutive years of heavy seeding by beech and mild winters, complicated assessment of the benefits of the technique for protecting breeding mohua. However, no stoat predation on breeding was
... However, protection of native fauna on the main islands of New Zealand is much more complicated for three main reasons: (1) there is a much larger suite of mammalian species on the main islands (in particular, four rodent species, three mustelid species, possums (Trichosurus vulpecula), hedgehogs (Erinaceus europaeus) and feral cats (Felis catus); King and Forsyth 2021), (2) there is the added complexity of periodic masting tree and tussock species driving dynamics of many communities and leading to rodent irruptions, spikes in mustelid populations and occasional prey switching to native species (Dilks et al. 2003;Monks and O'Donnell 2017;O'Donnell and Phillipson 1996;Pryde et al. 2005b), and (3) the competitive and predatory effects among species of introduced mammals come in to play (Bridgman 2012;Bridgman et al. 2013). ...
... io/ seedr ain_ shiny/. Predator control in the valley commenced with stoat trapping along a single transect running the length of the valley floor in 1997 (Dilks et al. 2003), but has progressively expanded to include bait station grids targeting rats timed in accordance with mast seeding of beech forest to protect bats and birds ...
... b A graphical representation of the effect of current landscape scale management strategies to control selected predators (black 'not allowed' symbols) on mice, Mus musculus (represented by change in text box and font size), which are not included in control efforts, and the consequent effect on the conservation goal of protecting lizards (represented by decreased oval size) are particularly vulnerable (Elliott 1996;Pryde et al. 2005b). Native bird populations that have recovered in response to the predator control are unlikely to be contributing to the overall trajectory of decline because native lizards coevolved with avian predators and display appropriate antipredator behaviours to them (Hoare et al. 2007b) and the vast majority of native birds are forest dwelling rather than occupying open habitat favoured by the skinks (Dilks et al. 2003). However, episodic predation by native and introduced predators other than mice may also contribute to the skinks' apparent inability to fully recover from impacts of mouse irruptions (e.g. ...
Invasive mammalian predators are a global biodiversity problem, particularly in archipelagos in which native fauna evolved in isolation from mammals. Landscape scale management of selected invasive mammalian predators is occurring across Aotearoa New Zealand to protect vulnerable forest birds and bats. In temperate southern beech forests, both predator irruptions and the timing of predator control is driven by mast seeding of beech trees. Relationships between predators targeted in this control, other invasive mammalian predators and other native taxa, particularly lizards and invertebrates, are poorly understood. We monitored southern grass skinks in the Eglinton Valley, Fiordland from 2009 to 2020 alongside monitoring of predators (stoats, rats and mice) in a system where predator control occurred in response to mast seeding. We evaluated relationships between skink abundance and abundance of rats (targeted in predator control operations) and mice (which also prey on small vertebrates like lizards, but are not controlled). Skink abundance declined over time and was negatively correlated with mouse abundance, but not correlated with rat abundance. Current landscape predator control to protect forest birds and bats is likely insufficient to protect ground-dwelling lizards, and may actually be detrimental to lizard populations if controlling the other predators contributes to a mesopredator release of mice. Mice are significant predators of a range of small vertebrates and large invertebrates, yet research into the sustainable suppression of mice to benefit vulnerable native populations is lacking. We strongly advocate for such research in order to deliver conservation management that benefits the full suite of biodiversity.
... The mohua (or yellowhead, Mohoua ochrocephala) is a small, insectivorous, forest passerine, endemic to the South Island of New Zealand. The species has had strong declines over the past decades (Dilks et al., 2003, O'Donnell, 1996 and has disappeared even from extensive areas of relatively unmodified native forest, thus this species is classified as "Nationally Vulnerable" (Robertson et al., 2012). The breeding strategy of mohua, which is a hole-nester with a long incubation time in late summer, makes their populations especially vulnerable to mammalian predators, which are highly abundant at the same time (Elliott, 1996). ...
... In particular, stoats were thought to be a main reason for the dramatic population declines in mohua when increasing in response to high rodent numbers after beech (Nothofagus spp.) tree mass seeding (masting) events (Choquenot, 2006). Nonetheless, ship rats (Rattus rattus) can also predate heavily on mohua after rapid population increases connected to factors like mild winters, beech masting or possibly high levels of stoat control (Dilks et al., 2003, Innes et al., 2010. ...
... Loh, pers comm., DOC, 2006). Similar beech mast events were seen in Eglinton Valley (Fiordland National Park) during 1999 and 2000, overlapping with several anecdotal reports of major increases in rodent abundance in many areas of the South Island during 2000 and 2001 (Dilks et al., 2003). High densities of rodents after such beech mast events can lead to unusually high densities of stoats (O'Donnell & Hoare, 2012), which then also prey on native birds. ...
Pest control using aerially-distributed 1080 bait could threaten non-target native bird species either by primary or secondary poisoning. To understand the impact of aerial 1080 control on the abundance of mohua (Mohoua ochrocephala), a vulnerable endemic forest bird, we analysed bird counts from the Catlins State Forest Park recorded over the period 1998-2002. Statistical modelling showed that mohua occupancy varied during the study and actually increased after 1080 control in 1999, but not significantly so. Concurrently with high predator numbers in the area during a beech (Nothofagus spp.) mast event, mohua abundance significantly declined in 2001 but then recovered in 2002. In conclusion, this study shows no negative effect for the nationally vulnerable mohua following a single aerial 1080 possum (Trichosurus vulpecula) control operation. In fact, with improvements in the experimental design and survey effort this study suggests future work could show positive effects of aerial possum control on populations, based on the increase in mohua occupancy observed directly after 1080 application.
... Wardle 1984;Schauber et al. 2002;Richardson et al. 2005). Years of high intensity beech seed production, known as a mast, significantly increase the available food for ship rats, resulting in a substantial increase in their numbers (King 1983;King & Moller 1997;Dilks et al. 2003). Establishing whether there is a link between ship rat elevational distribution and temperature is important, because in the next 100 years temperatures are predicted to increase as a result of climate change (Mullan et al. 2016). ...
... Establishing whether there is a link between ship rat elevational distribution and temperature is important, because in the next 100 years temperatures are predicted to increase as a result of climate change (Mullan et al. 2016). A temperature-induced increase in ship rat elevational distribution may negatively impact native species that have persisted at higher elevations (Elliott et al. 2010) and are vulnerable to being preyed on by ship rats (Dilks et al. 2003;Innes 2005). ...
... data), so the small amounts of seed recorded over the trapping study period were not an artefact of the sampling method. Similar increases in rat abundance after beech seeding have been recorded elsewhere in New Zealand (Blackwell et al. 2001;Dilks et al. 2003), and suggest a strong influence of food supply on ship rat populations. ...
There is a lack of information about how elevation affects the distribution of ship rats in New Zealand. In this study, ship rats (Rattus rattus) were captured in traps set along a 2 km elevational transect (455-1585 m a.s.l.) in beech (Nothofagaceae) forest and adjacent alpine tussock at Mt Misery, in Nelson Lakes National Park, from 1974 to 1993. A total of 118 rats were captured. In years with beech seed fall, upper range limits corresponded with the red beech forest (Fuscospora fusca) limit (~1030 m a.s.l.), with no rats caught above this line in the silver (Lophozonia menziesii) and mountain (F. cliffortioides) beech forest (1050-1408 m a.s.l.) or alpine zone (1425-1585 m a.s.l.). Binary generalised linear models indicated there is an indirect relationship between ship rat capture and temperature, as beech seed production, as well as decreasing elevation, were important predictors of rat capture. There was some evidence to suggest decreasing winter temperature and increasing annual precipitation also influenced ship rat capture and warrants further investigation. Our analyses provide an important insight into the drivers of ship rat elevational distribution, as well as providing a benchmark for comparing both current and future ship rat elevational distributions. Interrogation of more recent rat monitoring data from a range of beech forest types and sites is needed to test hypotheses around how warming temperatures, as predicted with climate change, will both directly and indirectly effect ship rat distribution.
... The rats have substantial impacts on native biodiversity during these irruptions, preying on native vertebrate and invertebrate species (e.g. Dilks et al. 2003;Innes 2005;McQueen & Lawrence 2008). If ship rats are to be controlled, monitoring methods will need to estimate trends in rat population abundance or distribution prior to an irruption event, as well as measuring the effectiveness of the rat control. ...
... However, this highlights the risk that widely dispersed lines may fail to detect localised outbreaks of rats and this could have a detrimental effect on native species. For instance, at Walker Creek, native bird species such as robin (Petroica australis) declined dramatically during the study period (Greene & Pryde 2012), while mōhua (Mohoua ochrocephala), a species sensitive to predators (Elliott 1996;Dilks et al. 2003), was absent. Both of these species maintain their presence in other parts of the Eglinton Valley where rats were less numerous (this study). ...
... Ship rats are traditionally hard to detect in beech forest between mast years (e.g. King 1983;O'Donnell et al. 1996;Dilks et al. 2003), so identifying factors that improve detection probability would be extremely useful. We found the presence of overnight rain significantly improved the probability of ship rat detection. ...
Reliable estimates of invasive pest mammal abundance and distribution in New Zealand are vital for effective conservation management of endangered native species. In this study, passive detection devices were used to monitor site occupancy by ship rats (Rattus rattus) in temperate rainforest in the Eglinton Valley, Fiordland, New Zealand. Ship rat occupancy was monitored on three grids of c. 100 ha each, containing 50 tracking tunnels spaced at 150-m intervals, for seven nights each in November 2004, January 2005 and March 2005. Site occupancy estimates were obtainable for only one of these grids, Walker Creek, where estimates increased by a factor of 2.5 over the total sampling period. Detection rates were highest within forest and forestedge habitats, and on nights with rainfall. In March 2005, 48 ship rats were caught in an effective trapping area of 132 ha. Removal trapping gave an estimated density of 0.38 rats ha–1 (0.36–0.48 rats ha–1, 95% confidence interval). Given the linear relationship between ship rat tracking and trapping rates, we are confident the reported trends in occupancy are realistic, and more accurate than tracking rate estimates. Improving the current monitoring methods so that the probability of detection can be estimated would be a good first step towards more accurate estimates of ship rat distribution.
... Measured density in mainland forests ranges from 1-12/ha [98]. Abundance indices for ship rats derived from trap catch or footprint tracking rates predictably surge after heavy seed masting of beech [99,100] or rimu trees [101]. However, the precise mechanisms behind these irruptions are not well known. ...
... In beech forests after a masting event, mouse numbers rapidly increase over winter, and by spring the well fed overwintered female stoats of all ages can minimize the intrauterine mortality of their litters [140]. In the early summer (8-9 months after the fall), huge numbers of newly independent young stoats appear [99]. Their numbers are due not to additional productivity of female stoats (as in weasels) but to a great improvement in juvenile survival of the litters conceived the previous year [138]. ...
New Zealand had no people or four-footed mammals of any size until it was colonised by Polynesian voyagers and Pacific rats in c. 1280 AD. Between 1769 and 1920 AD, Europeans brought three more species of commensal rats and mice, and three predatory mustelids, plus rabbits, house cats hedgehogs and Australian brushtail possums. All have in turn invaded the whole country and many offshore islands in huge abundance, at least initially. Three species are now reduced to remnant populations, but the other eight remain widely distributed. They comprise an artificial but interacting and fully functional bottom-up predator-prey system, responding at all levels to interspecific competition, habitat quality and periodic resource pulsing.
... Heavy beech seed production during mast years is associated with irruptions of rodents (house mouse Mus musculus and rat Rattus spp. especially ship rats) and stoats (King 1983;King & Moller 1997;Dilks et al. 2003), with consequent increased predation on native birds (Elliott 1996;O'Donnell 1996;Elliott & Kemp 2016). The increase in ship rat abundance in high-seed years is well known, but less is known about how this varies across altitudinal gradients or with pest control methods. ...
... Elliott et al. 2010). The response to seedfall is also well known (King & Moller 1997;Blackwell et al. 2003;Dilks et al. 2003;Harris et al. 2022) and is the underpinning of the Tiakina Ngā Manu/Battle for our Birds aerial 1080 campaigns carried out throughout the South Island by DOC in the 2014, 2016, and 2019 Nothofagus mast years (see www.doc.govt.nz/our-work/tiakina-nga-manu/). Future study of this topic could include testing for an altitude by seedfall interaction, which we were unable to include here due to the unbalanced nature of the dataset. ...
... For example, a fourth long-tailed bat colony in the study area was virtually extirpated following rat plagues of /2000and 2000(Monks and O'Donnell, 2017. In addition, predation by both stoats and rats also has significant impacts on forest birds that nest in similar tree cavities to bats in our Eglinton Valley study area (> 50% nest predation rates in untreated years: kaka, Nestor meridionalis Dilks et al., 2003; yellow-crowned parakeet, Cyanorampus auriceps Elliott et al., 1996b;mohua, Mohoua ochrocephala O'Donnell et al., 1996). Such cyclic population irruptions of rodents following pulses of super food abundance, like that provided by beech mast in New Zealand, are not unusual globally (e.g. ...
... Thus, the impact of predation each breeding season will vary not only with the frequency of predation attempts but also with the numbers of bats present in roosts, and whether lactating females are out of the roost foraging when a predator visits. When stoats climb trees in search of prey in the study area, they appear to focus on noise of fledgling birds being fed (Dilks et al., 2003;Elliott et al., 1996a), whereas rats appear to hunt systematically or randomly and mainly den in the canopy in cavities in the same beech trees occupied by bats (Pryde et al., 2005b;Smith et al., 2009). In addition, the length and magnitude of rat irruptions depends on the rat densities at the beginning of their spring growth period, over winter temperatures and when primary seed sources begin to germinate and thus are no longer available to them (J. ...
Invasive mammalian predators pose one of the greatest threats to biodiversity globally, particularly on oceanic
islands. However, little is known about the impacts of these invasive predators on bats (Chiroptera), one of the
most specious mammal groups, and one of the most widespread groups of mammals threatened on oceanic
islands (> 200 spp.). Nearly 50% of the world's threatened bats are island endemics and because they are often
the only native mammals on islands, they fulfil important ecological roles such as pollination and seed dispersal. Long-tailed bats (Chalinolobus tuberculatus) are critically endangered because of predation by exotic mammals, particularly ship rats (Rattus rattus), introduced by humans to the island archipelago of New Zealand. We monitored the survival of bats in three colonies in temperate rainforest in Fiordland over 22 years. Since 2009, we controlled predators during irruption phases and compared survival of bats in previously untreated areas with survival in forest blocks treated using rodenticides deployed in bait stations. Survival was estimated using multi-state mark-recapture models in Program Mark 7.0 with> 15,000 bats tagged. Survival was primarily dependent on year and age of bats, although seedfall intensity of the dominant canopy tree and predator management was also influential. Survival in long-tailed bats was as high as, or higher, than figures for bats generally in years with low predator numbers or predator control. Survival was markedly higher in treatment years when predators were managed (0.82 compared to 0.55). Population modelling indicated managed colonies will increase (λ > 1.05) whereas unmanaged colonies will decline (λ= 0.89−0.98) under scenarios that reflect increased frequency of beech mast and predator irruptions. Thus, effective predator control is essential for recovering long-tailed bat populations. Warming temperatures indicate that predator irruptions are becoming more frequent, which would require more predator control in the future than at present if declines in bat populations are to be reversed. These results are relevant to the conservation of threatened bats on oceanic islands, given the abundance of exotic mammalian predators, particularly ship rats, on them.
... The primary drivers are likely to include beech masting and consequent fluctuations in pest densities in adjacent forests that may have flow-on effects to pest densities above the timberline. The relationship between beech masting, subsequent plagues of rodents and stoats, and increased predation on sensitive species is well documented in forests (King 1983;Murphy & Dowding 1995;O'Donnell & Phillipson 1996;Dilks et al. 2003), but the form of such interactions in the alpine zone is unclear. Similarly, periodic heavy seeding of tussocks, and the fruiting and seeding of other alpine plants, may also drive predator cycles above the timberline, though only one study to date has documented these relationships (Wilson et al. 2006;Wilson & Lee 2010). ...
... There is also uncertainty about whether 'best practice' predator control would be effective in the alpine zone. Current 'best practice' for stoat control in forests involves intensive trapping Dilks et al. 2003) and/or secondary poisoning where Rattus spp. are the primary vector of the toxin 1080 (Gillies & Pierce 1999;Murphy et al. 1999). ...
Alpine zones are threatened globally by invasive species, hunting, and habitat loss caused by fire, anthropogenic development and climate change. These global threats are pertinent in New Zealand, with
the least understood pressure being the potential impacts of introduced mammalian predators, the focus of this review. In New Zealand, alpine zones include an extensive suite of cold climate ecosystems covering c. 11% of the land mass. They support rich communities of indigenous invertebrates, lizards, fish, and birds. Many taxa are obligate alpine dwellers, though there is uncertainty about the extent to which distributions of some species are relicts of wider historical ranges. The impacts of introduced mammalian predators are well described in many New Zealand ecosystems, though little is known about the impacts of these predators on alpine fauna. Here we review the importance of alpine habitats for indigenous fauna and the impacts of introduced mammalian predators; and develop a conceptual model explaining threat interactions. Most evidence for predation is anecdotal or comes from studies of species with wider ranges and at lower altitudes. Nevertheless, at least ten introduced predator species have been confirmed as frequent predators of native alpine species, particularly among birds and invertebrates. In the case of the endangered takahe (Porphyrio hochstetteri) and rock wren (Xenicus gilviventris), stoats (Mustela erminea) are primary predators, which are likely to be impacting significantly on population viability. We also document records of mammalian predation on alpine lizards and freshwater fish. While the precise impacts on the long-term viability of threatened species have not been evaluated, anecdotal evidence suggests that predation by mammals is a serious threat, warranting predator control. Future research should focus on predicting when and where mammalian predators impact on populations of indigenous fauna, furthering our understanding of the alpine predator guild particularly through adaptive management experiments, and exploring interactions with other threats.
http://newzealandecology.org/nzje/3300.
... The strong relationship between beech mast seeding events, irruptions in populations of introduced rodents and mustelids and subsequent prey-switching to native vertebrate populations when the seed source is depleted is well described (O'Donnell & Phillipson, 1996;Dilks et al., 2003;Pryde et al., 2005). Our case study contributes strong circumstantial evidence that the extinction of a colony of threatened long-tailed bats was caused by the irruption in key predators as a result of the double mast seeding event in 1999-2001 (Fig. 1). ...
... Our case study contributes strong circumstantial evidence that the extinction of a colony of threatened long-tailed bats was caused by the irruption in key predators as a result of the double mast seeding event in 1999-2001 (Fig. 1). The simultaneous crash in the Eglinton Valley population of m ohua (Mohoua ochrocephala), a threatened, endemic, hole-nesting bird that is similarly vulnerable to predation by rats and mustelids (Dilks et al., 2003), provides further support for this thinking. Episodic predation events in other vulnerable, native vertebrate populations (e.g. ...
Strong social structuring within a population can confer fitness advantages to group members, but may also affect the ability of a population to recover from local extinctions. Opportunities to evaluate the dynamics of the collapse of a sub-population on a vertebrate population in the wild are rare, requiring a crash during a long-term study of marked individuals. Endangered long-tailed bats Chalinolobus tuberculatus, which are members of the widespread family Vespertilionidae, live in closed social groups as evidenced by non-random associations of individuals and a low degree of mixing among colonies. During a 19-year mark-recapture study of long-tailed bats in the Eglinton Valley, New Zealand, one colony of bats collapsed over a 2-year period in which numbers of introduced predators were high. We investigated individual- and colony-level implications of this local extinction event. Survivors (11 known) were assimilated into the neighbouring colony during and immediately after the collapse, but retained higher association rates with individuals from their former colony. The neighbouring colony gradually extended its roosting range into habitat formerly occupied by the extinct colony. Acceptance of individuals into other colonies demonstrates resilience of highly structured vertebrate populations to local crashes.
... Some of these declines appeared to correspond with local irruptions of ship rats due to beech masts (e.g. Studholme 2000), and predation of mōhua by rats has also been observed (Dilks et al. 2003). ...
The role of vegetation in the relationship between microhabitat and ship rat (Rattus rattus) distribution remains poorly understood. We used three years of trapping data (2017–2020) to calculate capture rates for 97 traps in the Makarora Valley and Haast Pass areas of Mt Aspiring National Park and determined aspects of the vegetation surrounding traps that influenced capture rates. The presence of fruiting understory plants—round-leaved coprosma (Coprosma rotundifolia), horopito (Pseudowintera colorata), and wineberry (Aristotelia serrata)—had weakly significant and positive associations with rat captures, whereas increasing density of large (> 200 mm DBH) mountain beech (Fuscospora cliffortioides) trees had a negative association, which was highly significant. Future research should incorporate methodology that links seasonal food abundances to capture rates and explores the influence of edge effects.
... Some of these declines appeared to correspond with local irruptions of ship rats due to beech masts (e.g. Studholme 2000), and predation of mōhua by rats has also been observed (Dilks et al. 2003). ...
There have been numerous declines and extinctions of native fauna in Aotearoa New Zealand since human settlement. Against this background of loss there have been remarkable advances in conservation management, including the use of conservation translocations to reduce extinction risk and restore depauperate
ecosystems. Here we review conservation translocations in Aotearoa New Zealand. Our review assembles knowledge from Aotearoa New Zealand’s rich history of faunal translocations and describes six key considerations for successfully establishing translocated populations: (1) What values will be met by a translocation? (2) What is the natural and conservation history of the translocation candidate? (3) Does the release site habitat match that of the proposed source population, and if not, why is the release site considered appropriate and can management ameliorate differences? (4) Will dispersal be a problem? (5) Will genetic management be required and how realistic is it that this management will be implemented? (6) What do future developments mean for the management of translocated populations? We discourage a focus on any single element of translocation planning but rather encourage all people involved in translocations, particularly decision makers, to explicitly recognise that successful translocations typically have multiple, values-based objectives. We also support recommendations that the principles of good translocation decision-making are embedded in government policy.
... However, these outcomes imply that toxicant-based control of stoats requires the presence of multiple pest mammals, which is not a given. Direct targeting of stoats has relied primarily on standard trapping methods (e.g., Dilks et al. 2003, McMurtrie et al. 2008, though early efforts to develop humane, stoat-specific traps were relatively unsuccessful (Murphy and Fechney 2003). Regardless of the method(s) used, complete eradication of stoats has been achieved only on a few islands that are outside their swimming range (DOC 2017). ...
... Santulli et al., 2014), New Zealand (e.g. McLennan et al., 1996Dilks et al., 2003;King & Powell, 2011) and a number of island systems where these effects are often intensified. Unfortunately, many small carnivore species are endemics of developing countries such as those in Asia and Africa, where their status and distribution have never been thoroughly assessed. ...
The absences of large carnivores from many ecosystems, human‐induced landscape changes, and resource supplementation have been theorized to increase the abundance of small carnivore species around the world. Overabundant and/or unconstrained small carnivores can have significant effects on specific prey species that, in some cases, can cascade through entire ecosystems. Here, we review the effects of small carnivores on threatened species. We focus on four well‐studied families (Procyonidae, Mephitidae, Mustelidae, and Herpestidae) and emphasize that this is a global conservation issue with consequences for biodiversity. We review and compare the impacts that small carnivores can have on a variety of prey taxa including small mammals, nesting avian and reptilian species, and rare invertebrates. We differentiate between native and exotic small carnivores because this is often an important distinction in terms of the impact severity and range of effects. In addition to direct lethal effects (i.e. predation), small carnivores can also impact threatened species as disease vectors and through competition or overexploitation, which can disrupt communities via ecological release or extinction. Furthermore, we explore other case studies in which small carnivores have had positive effects on threatened species and discuss studies that reveal other taxa responsible for exerting stronger negative effects on threatened prey. We offer some concluding remarks about global small carnivore conservation and emphasize the need for decision‐analytic approaches and robust analyses that can improve our assessment of how populations of threatened species can be affected. To date, indirect effects are especially difficult to measure in the field and many studies have provided only anecdotal or correlative results, signalling a need for improving our scientific methodologies and management approaches.
... The cascade of events starting with masting and culminating in stoat irruptions is well described for the main ecosystems inhabited by kea: a mast-driven rodent irruption fuels a subsequent stoat irruption, which commences at the start of the year following the mast year and lasts for 1-2 years (King 1983;King et al. 2021). Post-mast carnivore irruptions are strongly associated with poor demographic performance of native birds and bats O'Donnell and Phillipson 1996;Dilks et al. 2003;Pryde et al. 2005;Kemp et al. 2018). Controlled experiments have demonstrated improved demographic performance where stoat irruptions have been suppressed by traps and or poison baits Moorhouse et al. 2003;Kemp et al. 2018). ...
Invasive carnivores are threatening the indigenous fauna of Aotearoa, but impacts vary with time, space and species. Conservation strategies require knowledge of predator-prey dynamics specific to different ecosystems and allowing for long-term guild shifts. To build this knowledge, we model the survivorship of the kea, a long-lived, ground-nesting parrot with an expansive species-range, using a dataset spanning two decades (1998–2021) and spanning several forest-dominated South Island montane ecosystems. Kea survivorship was lower in eastern ecosystems compared to western ones, depressed during carnivore irruptions, and elevated after predator control. Kea of all ages and both sexes fell prey to stoats and feral cats whilst foraging and roosting, not whilst nesting. Stoat depredation happened in all ecosystems, whereas feral cats featured more in eastern ones. Annual survivorship was high in most contexts (adults > 90%, juveniles > 70%), but a peak in stoat and feral cat predation in eastern ecosystems during 2020–2021 reduced adult survival to <60%. This predation peak followed a rodent population crash, the primary prey of carnivores in eastern beech forests. We conclude that predator impacts on kea are concentrated into post-mast years. Recommendations for management are provided.
... Current control techniques for stoats in New Zealand rely mainly on networks of kill traps [4]. These may be run year-round to maintain low predator pressure [15][16][17], only during the bird breeding season, or in response to a stoat population irruption [18,19]. Such trapping programmes require effective long-life lures that will be attractive to all members of the pest population. ...
Eradication and control methods to limit damage caused to native biota in New Zealand by the stoat (Mustela erminea) rely on effective lures for trapping and detection devices, such as cameras. Long-life semiochemical lures have the potential for targeting stoats in situations where food-based lures are of limited success. The attractiveness of body odours of captive stoats was tested in a series of captive animal and extensive field trials to investigate their potential as trapping and monitoring lures. Stoats approached and spent significantly more time sniffing stoat urine and scats and bedding from oestrous female stoats than a non-treatment control. The bedding odours were attractive in both the breeding and the non-breeding season. Stoats also spent significantly more time sniffing oestrous stoat bedding than female ferret bedding, but the ferret odour also produced a significant response by stoats. In the field trials, there were no significant differences between the number of stoats caught with food lures (long-life rabbit or hen eggs) compared with oestrous female or male stoat bedding lures. These results indicate the potential of both stoat bedding odour and the scent of another mustelid species as stoat trapping lures that likely act as a general odour attractant rather than a specific chemical signal of oestrus.
... Outcome monitoring data for entire bird communities, with adequate baselines or controls, have been published for only a few New Zealand restoration sites (Dilks et al. 2003;Graham et al. 2013;Miskelly 2018;Bombaci et al. 2018;Fea et al. 2020;Ralph et al. 2020), with robins and kākā consistently among the species that benefitted from pest mammal eradications. However, O'Donnell & Hoare (2012) did not detect any increase in kākā in response to pest mammal control in the Landsborough Valley, South Westland. ...
Recent advances in the control of mammalian predators have begun to reveal interspecific competition as a key driver in the structure of New Zealand forest bird communities once predation pressure is reduced. We present evidence that, when at high densities, South Island robins (Petroica australis) may be responsible for declines in a suite of smaller native and introduced songbird species. Bird surveys undertaken on 47 islands in Breaksea Sound and Dusky Sound, Fiordland, during 1974 to 1986, were repeated on the same islands in 2016 or 2019. During the first block of surveys, Norway rats (Rattus norvegicus) were present on two islands, and stoats (Mustela erminea) were known or presumed to regularly reach 43 of the remaining islands. The rats were eradicated in 1986 and 1988, and stoats have been controlled to zero density since 2001 on all 28 of the islands surveyed in Dusky Sound, and since 2008 on 12 of 19 islands surveyed in Breaksea Sound. Bird species that apparently benefited from pest mammal eradications included South Island robin (Petroica australis) and kākā (Nestor meridionalis), both of which are endemic. Species recorded less often after the eradications included tomtit (Petroica macrocephala), grey warbler (Gerygone igata), silvereye (Zosterops lateralis), dunnock (Prunella modularis), and chaffinch (Fringilla coelebs) – a mixture of endemic, native, and introduced species. We hypothesise that these five species have been outcompeted or displaced by the now widespread and abundant South Island robin, probably through aggressive interactions.
... 1080 (sodium fluoroacetate) over a small part (56 km 2 ) of the estimated white-tailed deer habitat range. The operations targeted rats directly and stoats by secondary poisoning, to protect mohua from increased predation resulting from surges in rodent populations as a result of beech mast events (O'Donnell and Phillipson 1996;Dilks et al. 2003;P.C.E. 2017). ...
Intensive ground-based searches for white-tailed deer carcasses were conducted in the Dart Valley/Routeburn catchments following the aerial application of 1080 (sodium fluoroacetate) cereal pellets as part of the ‘Battle for the Birds’/ Tiakina Ngā Manu predator control program in August 2014. Four 100 ha areas were searched over four days. The detection rate of simulated carcasses allowed an estimation of the success rate for finding deer carcasses. All white-tailed deer carcasses located were confirmed to have muscle tissue containing traces of 1080 (range: 0.41–1.06 mg/kg). The detection rate of simulated carcasses was 78% (312/400). The adjusted number of dead white-tailed deer was 3.85 ± 0.85 (95% CI) over the 400 ha (0.96 deer/km²) suggesting a potential mortality of 146 ± 32 (95% CI) white-tailed deer in the predator control area of 15,215 ha. These results suggest that recurrent predator control operations may have implications for sustainable hunting of white-tailed deer.
... Although we had limited sample sizes for these species in our study, previous work demonstrates the vulnerability of these species to predation from introduced mammals (O'Donnell 1996; Innes et al. 1999;Basse et al. 2003;Dilks et al. 2003;Hooson & Jamieson 2003;Taylor et al. 2005;Toy et al. 2018), and these species have been brought close to extinction on New Zealand's mainland since the introduction of mammalian predators. The absence of these deeply endemic species across many sites in our meta-analysis-weakened our results because these species likely had the most negative responses at sites lacking mammal control and the most positive responses to high-intensity mammal control. ...
Over the past 1000 years New Zealand has lost 40–50% of its bird species, and over half of these extinctions are attributable to predation by introduced mammals. Populations of many extant forest bird species continue to be depredated by mammals, especially rats, possums, and mustelids. The management history of New Zealand's forests over the past 50 years presents a unique opportunity because a varied program of mammalian predator control has created a replicated management experiment. We conducted a meta‐analysis of population‐level responses of forest birds to different levels of mammal control recorded across New Zealand. We collected data from 32 uniquely treated sites and 20 extant bird species representing a total of 247 population responses to 3 intensities of invasive mammal control (zero, low, and high). The treatments varied from eradication of invasive mammals via ground‐based techniques to periodic suppression of mammals via aerially sown toxin. We modeled population‐level responses of birds according to key life history attributes to determine the biological processes that influence species’ responses to management. Large endemic species, such as the Kaka (Nestor meridionalis) and New Zealand Pigeon (Hemiphaga novaeseelandiae), responded positively at the population level to mammal control in 61 of 77 cases for species ≥20 g compared with 31 positive responses from 78 cases for species <20 g. The Fantail (Rhipidura fuliginosa) and Grey Warbler (Gerygone igata), both shallow endemic species, and 4 nonendemic species (Blackbird [Turdus merula], Chaffinch [Fringilla coelebs], Dunnock [Prunella modularis], and Silvereye [Zosterops lateralis]) that arrived in New Zealand in the last 200 years tended to have slight negative or neutral responses to mammal control (59 of 77 cases). Our results suggest that large, deeply endemic forest birds, especially cavity nesters, are most at risk of further decline in the absence of mammal control and, conversely suggest that 6 species apparently tolerate the presence of invasive mammals and may be sensitive to competition from larger endemic birds.
... Avian communities are particularly susceptible to external disturbances, with invasive species being responsible for 58.2% of known bird extinctions since 1500 (Szabo et al. 2012). Increasingly, research demonstrates that introduced mammals including rodents, e.g., rats and mice (Thibault et al. 2002, Ratcliffe et al. 2009), mustelids (Ferreras and Macdonald 1999, Moller and Alterio 1999, Dowding and Murphy 2001, Dilks et al. 2003, Kelly et al. 2005, and feral cats (Bonnaud et al. 2007, Balogh et al. 2011, Loss et al. 2013, Woinarski et al. 2017) pose a major threat to some bird populations. ...
The House Sparrow (Passer domesticus), native to Europe and Asia, has been introduced globally and is now one of the most ubiquitous birds in the world. In North America, these invasive passerines compete with native species for nest cavities, which are often limited. Because of the difficulties of extirpating an invasive species and the growing desire from the public to help in conservation matters, we sought to test a potential technique for managing invasive cavity-nesting passerines that could be successfully deployed by professionals and citizen scientists alike. Previous studies demonstrate that applying vegetable oil to eggs is a nontoxic management technique often used to manage unwanted waterfowl. Further, egg oiling is a technique that is acceptable to a large segment of the public. This study assesses the efficacy of applying vegetable oil for preventing House Sparrow eggs from hatching, reducing the number of fledged young, prolonging incubation time, and delaying renesting attempts by the adults. We sprayed treatment clutches once with approximately 0.8 ml of vegetable oil early in the developmental period and subsequently monitored nests every 3-4 days. The application of vegetable oil to treated eggs was 100% effective at preventing hatching and, thus, preventing any offspring from fledging. Furthermore, the adults in the treatment group incubated their eggs for nearly twice as long as the adults at control nests, reducing their opportunity to produce more clutches later in the season. Given the availability, low cost, and effectiveness of applying vegetable oil to eggs to prevent the reproductive output of invasive cavity-nesting passerines, we propose that this method can be easily implemented by wildlife managers as well as trained nest box stewards.
... Extensive forests of southern beech trees (Nothofagus spp.), which are important conservation reserves for many of the remaining endemic bird species and also bats (O'Donnell 1996, Sedgeley andO'Donnell 1999), produce an abundance of seeds in autumn (March-June) every few years. Such pulses of seed production (or seed masting) provide an abundant resource for seed-eating bird species and their introduced predators (King and Moller 1997, Dilks et al. 2003, King and Powell 2011. Consequently, populations of these invasive mammal species flourish during spring and summer following a seedmasting event and, consequently, induce subsequent increases in mortality and failures in recruitment among threatened native birds (O'Donnell 1996). ...
PhD Research: QUANTIFYING IMPACTS OF INVASIVE APEX MAMMALIAN PREDATORS ON BELOWGROUND-ABOVEGROUND FOOD-WEB INTERACTIONS
... Our results corroborate previous studies demonstrating that impacts of feral cats on island bird populations can be especially severe (Blackburn et al. 2004, Clavero et al. 2009, Jones and Merton 2012, and we echo the call of implementing cat control to increase the survival of native birds (Courchamp et al. 2003, Nogales et al. 2004. Although research on post-fledgling survival has increased in recent decades (Cox et al. 2014), few studies have addressed the impacts of invasive predators on this demographic parameter, particularly within island ecosystems (but see Dilks et al. 2003, Keedwell 2003, Moorhouse et al. 2003, Reauleaux et al. 2014. Our findings indicate that these impacts can be severe, yet we are optimistic that suppressing invasive predator populations and making informed conservation decisions (e.g., where to place nest boxes on the landscape) can facilitate the success of native birds on Guam and in other island ecosystems. ...
Invasive predators have caused widespread loss of biodiversity in island ecosystems, yet certain species are able to tolerate the presence of generalist invaders. For example, the invasive brown treesnake (BTS; Boiga irregularis) caused the extirpation of 10 of 12 native forest bird species on the island of Guam, but a remnant population of the Micronesian Starling (Aplonis opaca), or Såli, has managed to persist on a military installation in northern Guam. Understanding how Micronesian Starlings are coping with the presence of BTS can inform conservation efforts for island bird populations facing invasive predators and provide insight into strategies for expanding the starling population. We monitored the survival, movements, and habitat use of 43 radio-tagged starling fledglings during this vulnerable life-history stage. Invasive predators accounted for 75% of fledgling mortality (56% from BTS; 19% from feral cats) and contributed to one of the lowest post-fledging survival rates (38% through day 21 post-fledging) recorded for passerine birds. Predation by BTS persisted at elevated rates following natal dispersal, further reducing cumulative survival to 26% through 53 days post-fledging. Nest location was an important predictor of survival: fledglings from nest boxes closer to the forest edge were more likely to use forest habitat at younger ages and more likely to be depredated by BTS. Overall, our findings indicate that BTS continue to severely impact Guam’s starling population, even more so than invasive predators affect native birds in other island systems. We recommend deploying nest boxes farther from the forest to improve fledgling survival and implementing urban predator control to promote growth of the Micronesian Starling population on Guam and facilitate future reintroductions of other species.
... Therefore, stoats and cats might limit kea populations. Rats, conversely, are unlikely to limit kea populations, based on studies of kākā (Beggs & Wilson 1991;Wilson et al. 1998;Dilks et al. 2003;Moorhouse et al. 2003;Powlesland et al. 2003). However, rats may impact kea near the end of mast years, when rat populations peak while kea are nesting. ...
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.
... Lethal control of invasive predators may improve the survival and recovery of some native species. In Australia, the control of stoats (Mustela erminea) has increased the reproductive and survival rates of native bird species (Dilks et al. 2003). However, there are consequences to the lethal control of invasive predators. ...
The implementation of mammal predator killing programs is highly controversial and deserves discussion within the scientific community. In this opinion paper, I use specific examples to discuss the whys and hows of programs aimed at: 1) ensuring human safety and health; 2) addressing concerns of interest groups; and 3) safeguarding native and endangered species. Successful programs share some commonalities: they focus on the main factor that is responsible for the problematic situation and on culprit animals, and they are developed with an understanding of the ecology and behaviour of the predators. Public support for such programs requires that killing methods be species-specific, humane, and effective. I propose a stepwise strategy to properly assess the causes of human ̶ predator conflicts and determine if a killing program should be implemented.
... Although latitude is not a significant factor in explaining extinc- tion risk among parrots globally ( Olah et al. 2016), it appears to be a significant factor in Oceania, with higher-latitude species more likely to be threatened (Table 2). This is possibly driven by the relatively high proportion of threatened parrots in Tasmania and New Zealand (Figure 3(B)), which have suffered from the introduction of non-native predators ( Dilks et al. 2003;Heinsohn et al. 2015). ...
Australia, New Zealand, New Guinea, Wallacea, and the islands of the Pacific Ocean collectively possess 42% of the world’s parrot species, including half of all Critically Endangered species. We used comparative methods to review the factors related to extinction risk of 167 extant and 5 extinct parrot species from this region, subsequently referred to as ‘Oceania’. We tested a range of ecological and socio-economic variables as predictors of extinction risk for parrots in the region while controlling for phylogeny. Parrot species were most likely to be threatened if they had small historical ranges, large bodies, or a high dependency on forest, or if they were endemic to a single country, or native to a country with high unemployment. Our analysis identifies invasive species as an especially severe threat to the parrots of Oceania. We present maps of parrot species’ diversity and draw attention to regions of conservation concern. Our comparative analysis presents an important overview of the factors contributing to the decline of parrots in Oceania, and provides a strong basis for comparison with other parts of the world.
... Since their introduction to New Zealand in the 1880s, in an attempt to control rabbits, stoats have become major predators of indigenous fauna across a full suite of available habitat types (Elliott 1996;Elliott et al. 1996;McLennan et al. 1996;Wilson et al. 1998;Ratz and Murphy 1999;Cuthbert et al. 2000;Murphy et al. 2004;Smith et al. 2008b;O'Donnell et al. 2015O'Donnell et al. , 2016. Stoat populations erupt periodically in southern beech (Nothofagaceae) forests in response to mast seedfall events (King 1983;Dilks et al. 2003). However, in most years and habitat types, stoats in New Zealand are at low densities and are sparsely distributed, having large home-range sizes and dispersing extensive distances (Murphy and Dowding 1994;Murphy and Dowding 1995;Alterio et al. 1998;Smith and Jamieson 2005;Smith et al. 2007). ...
Context The ability to monitor the spatial distribution and abundance of species is essential for detecting population changes, and assessing the progress of conservation management programs. Stoats (Mustela erminea) are a serious conservation pest in New Zealand, but current monitoring methods are not sensitive enough to detect stoats in all situations. Aims We compare the effectiveness of the most commonly employed method for monitoring mustelids in New Zealand, footprint-tracking tunnels, with two alternative detection methods, camera traps and artificial nests. We were interested in determining whether alternative detection methods were more sensitive in detecting stoats than tracking tunnels. Methods We established a network of tracking tunnels, artificial nests and camera traps within alpine habitat. Devices were checked for stoat detections weekly across two seasons, in spring-early summer and autumn. Differences in detection rates and cost effectiveness among methods were analysed among seasons. Key results In spring-early summer, the time to first stoat detection using footprint-tracking tunnels was 61 days, compared with 7 days for camera traps and 8 days for artificial nests. The rate of stoat detection using artificial nests was significantly higher than it was using tracking tunnels (coef≤3.05±1.29, P≤0.02), and moderately higher using camera traps (coef≤1.34±1.09, P≤0.22). In autumn, when overall detectability of stoats was higher, there was no significant difference in detection rates among the three methods, although camera traps again recorded the earliest detection. Artificial nests were the most cost effective detection method in both seasons. Conclusions Artificial nests and camera traps were more efficient at detecting stoats during their spring breeding season (when they are known to be difficult to detect), compared with the more established footprint-tracking tunnel method. Artificial nests have potential to be developed into a monitoring index for small mammals, although further research is required. Both methods provide an important alternative to footprint tracking indices for monitoring stoats. Implications Our study demonstrated the importance of calibration among different monitoring methods, particularly when the target species is difficult to detect. We hypothesise that detection methods that do not rely on conspicuous, artificially constructed devices, may be more effective for monitoring small, cryptic mammals.
... We recorded the consumption of bulbs, stems, and flowers of this species, but also of fruits, although we did not sample diet during its fruiting period (Schäffer 2005). We believe that the fruiting of the invasive H. gardnerianum may favour the abundance of rats during the autumnwinter period because black rat populations are described to often erupt after heavy fruiting or seeding of forest trees (Daniel 1978;King and Moller 1997;Dilks et al. 2003;Harper 2005). ...
On São Miguel Island, Azores (Portugal), introduced rodents may constrain conservation efforts being taken on the Macaronesian laurel forest. With the aim of assessing their foraging ecology in one of the last patches of native laurel forest, we carried out snap-trapping sessions to evaluate rodent relative abundance and diet in three habitats (exotic forest, forest plantation, and forest opening) during winter, spring, and summer. Two species (Rattus rattus and Mus musculus) were captured, and capture rates were higher in winter, particularly in native laurel forest, followed by a decrease in all habitats, with the exception of forest plantation. Stomach contents' analysis showed that invertebrates, mainly Annelida and Arthropoda, made up the greatest part of both species' diet in the four habitats, but there was an important component of plant consumption, with a large bulk corresponding to the exotics Cryptomeria japonica and Hedychium gardnerianum. Our results show that temporal variations on the relative abundance and diet of these rodents were more significant than habitat variations.
... (McLennan et al. 1996), whio Hymenolaimus malacorhynchos (Whitehead et al. 2008) and kākā Nestor meridionalis (Wilson et al. 1998). Both ship rats and stoats have certainly contributed to further declines of native fauna, especially after mast years in beech forests (Dilks et al. 2003). Unfortunately, the historical coincidence that saw weasels, stoats and ship rats arrive in the South Island at about the same time means that the proportions of damage to be attributed to each were and are impossible to determine. ...
This paper reviews the timing and spread of weasels and stoats across the South and North Islands of New Zealand during the late nineteenth century, entirely from historical records. The flavour of the debates and the assumptions that led to the commissioning of private and government shipments of these animals are best appreciated from the original documents. I describe the sites of the early deliberate releases in Otago, Canterbury, Marlborough, and Wairarapa, and list contemporary observations of the subsequent dispersal of the released animals to named locations in Southland, Westland, Wellington, Hawke’s Bay, Auckland and Northland. Originally, weasels were landed in far greater numbers than stoats (2622 weasels and 963 stoats listed in shipment records) and, while at first they were very abundant, they are now much less abundant than stoats. Two non-exclusive hypotheses could explain this historic change: (1) depletion of supplies of their preferred small prey including birds, mice, roosting bats, lizards, frogs and invertebrates, and (2) competition with stoats. Contemporary historic written observations on the first impacts of the arrivals of weasels and stoats on the native fauna offer graphic illustrations of what has been lost, but usually failed to consider the previous impacts of the abundant rats (Rattus exulans since the late 13th century, and R. norvegicus since 1770s-90s), and cannot now be distinguished from the activities of R. rattus arriving in the 1860s-90s.
... Mast years increase food supply for mice (Mus musculus) and rats, frequently causing irruptions in their populations (O'Donnell & Phillipson 1996), which in turn results in increased food supplies and hence prolific breeding of stoats, with up to 13 young raised per female in years when rodents are abundant (King 2005). Native species including bats are then at risk from these predators and controlling them in these years has been found to be essential for their long-term survival Dilks et al. 2003;Pryde et al. 2005). ...
Introduced mammalian predators, in particular rats (Rattus spp.), are a major threat to New Zealand bat populations. Aerial application of the toxin sodium monofluoroacetate (1080) is currently the most costeffective method of controlling rats across large spatial extents. Lesser short-tailed bats (Mystacina tuberculata) may be vulnerable to secondary poisoning from 1080 because they feed on invertebrate prey on the ground that may have consumed toxic bait. We monitored individually marked bats before, during, and after an aerial 1080 operation in the Eglinton Valley, Fiordland, in December 2014 from a population that has been monitored since 2008. No symptoms of sub-lethal exposure in free ranging bats were detected and survivorship was high: 764 of the 771 marked bats (99.1%) recorded in the pre-monitoring period were still alive one week after toxin application and a record number of 1731 marked bats were recorded emerging from a single roost tree in January 2015. One bat pup was found dead under a roost tree and 1080 was detected in muscle tissue. Any immediate impact of 1080 was assessed as minimal because the calculated annual survival rates were high (91.5%). We conclude that survival of the population was likely enhanced by the large scale 1080 operation.
... Optimal pest control strategies must also consider the influence of food availability on pest populations. Food availability can be an important determinant of rat population growth in New Zealand forests (Blackwell et al. 2003;Dilks et al. 2003;Innes 2005;Sweetapple & Nugent 2007;King & Powell 2011). Thus, the availability of preferred foods (fruit, seeds and invertebrates) is likely to influence the length of time that rodent abundance is reduced after control (Studholme 2000;Sweetapple & Nugent 2007). ...
We examined spatiotemporal changes in rat tracking indices following large-scale (>10 000 ha) pest control using aerial applications of sodium monofluoroacetate (1080) baits in Tararua Forest Park, North Island, New Zealand. Population control of rats appeared effective, with few to no rat tracks recorded in treatment areas during the 6 months after control. However, the rat tracking index increased rapidly after that, and 24-30 months after control, rat tracking indices in treated areas exceeded those in the non-treated areas. Rat tracking indices first increased at the treatment margins (6-12 months post-control), with rat recovery in the centre of controlled areas delayed by 24-30 months. The best supported statistical model of rat tracking indices included an interaction term between time since treatment*distance to non-treatment area, which indicated that overall increases in rat tracking after control were highest at monitoring lines located in the interior of the control zone, with a negative growth rate estimated for lines located outside of the control area. This suggests a competitive release for rat populations in the interior of the control zone. The observed delay in rat recovery on the interior lines compared with lines located at the control margin implies that rat population increase following control was initiated by rats migrating into the treated area from adjacent untreated forest areas. Treatment persistence, therefore, might be increased by increasing the size of pest control areas; aligning pest control boundaries with immigration barriers, such as large water bodies and/or alpine zones; or implementing intensive pest control around treatment boundaries to intercept immigrating rats.
... ha (MCP=100%) on Mokoia Island (Stephenson 1998 to be related to food supply and habitat (Lurz et al. 2000). Southern beech forests generally have low productivity (Wardle 1984) with periodic mast events (Dilks et al. 2003) so home ranges may be relatively large to cope with low productivity years. In North Island podocarp hardwood or regenerating secondary forests, invertebrate productivity is probably higher and available food for rūrū more plentiful (Moeed & Meads 1986). ...
Nocturnal species are challenging to monitor, but with advances in bioacoustic technology, acoustic monitoring is becoming a more affordable, efficient technique for monitoring cryptic species. We tested the suitability of acoustic monitoring as a potential national monitoring method for morepork/rūrū (Ninox novaeseelandiae), in beech forest within the Eglinton Valley, Fiordland, during spring 2009–2010. We used radio telemetry and an acoustic call study to address two questions to help managers make evidence-based decisions on the spacing of acoustic call count stations: (1) What are the sex-specific and seasonal home-range sizes of rūrū? (2) How does acoustic detection decrease with increasing distance? Home ranges were the largest recorded to date for rūrū in New Zealand (mean 100% MCP = 307 ha, mean 75% kernel = 43.5 ha) with an average range spread of 270 m (75% kernel). Significant attenuation of recorded calls occurred after 150 m in southern beech (Nothofagaceae) forest and no calls could be detected by the recorders beyond 250 m. Acoustic monitoring is a promising technique to monitor rūrū nationally, but the spacing of stations needs to vary depending on home-range, habitat and the microphones used in the acoustic detectors.
... 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.
... Therefore, missing 5% of females would not be satisfactory for an island eradication, nor for some mainland management scenarios where endangered species are present that are highly sensitive to stoat predation. Our example of stoats in New Zealand is one where managers will almost always want to intersect a high proportion of home ranges, because of the sensitivity of endemic birds to stoat predation (Wilson et al. 1998;Innes et al. 1999;Dilks et al. 2003;Whitehead et al. 2008). However, there may be management scenarios with other invasive species where it is not necessary to strive to intersect 100% of the home ranges of the target animal in the management area. ...
Invasive species have been identified by the Convention on Biological Diversity as a significant threat to biodiversity. Conservation managers often lack tools for addressing uncertainty about the control intensity required to achieve cost-effective management of invasive species. We describe a modelling approach for informing the spacing of control-device lines given the availability of home-range data. To demonstrate its utility, we used data on stoats (Mustela erminea), an introduced mammalian predator responsible for the decline of endemic birds in New Zealand. We calculated home-range widths using three methods: kernels, circles and the narrowest distance across the raw point data. Using the widths from each method, we then permuted iteratively the relative location and orientation of home ranges between control-device lines, and calculated the probability of encounter with varying distances between lines. Widths across raw points gave lower estimates of the probability of encounter of device lines than kernels, while circles gave estimates that were intermediate between the two. For stoats, the simulation on point-data widths indicates that to ensure control-device lines will intersect 100% of female stoat home ranges they need to be <= 400 m apart, while the simulation on kernels and circles allowed <= 700 m. When needing to address uncertainty about the intensity of control to apply, managers should give priority to the collection of home-range data so that control-line spacing can be determined using the simulation described. If sufficient home-range data are available then simulating kernels provides better predictions, otherwise simulating the width across point data provides a conservative option when such data are insufficient.
... Some of the differences in stoat diet between the sites may also have been a consequence of being sampled in different years. The Chalky Island stoat eradication programme was conducted in 1999, a beech mast year in Fiordland (Dilks et al. 2003;Kelly et al. 2013). Beech seeds are a nutritious food source (Murphy 1992) and forest birds and invertebrates, as well as rodents, increase in abundance in mast years (Murphy & Dowding 1995;Alley et al. 2001;O'Donnell & Hoare 2012). ...
The eradication operations to remove stoats (Mustela erminea) from islands in Fiordland provided
an opportunity to assess the diet of stoats in areas with no rodents or with only mice (Mus musculus) available as mammalian prey. The carcasses of stoats trapped on Chalky Island in 1999, Secretary Island and the adjacent mainland in 2005, and Resolution Island in 2008 were collected and their gut contents analysed. On rodent-free Chalky Island, most of the stoats had consumed birds, mostly passerines. Stoats on Secretary Island (rodent free) and Resolution Island (mice present) preyed mostly on invertebrates, particularly wētā (Orthoptera). On Resolution Island, mice were probably at relatively low densities, and were consumed by only 12% of the stoats. While average consumption of birds and invertebrates was lower for stoats at the mainland site, the only significant differences amongst the sites were the high bird consumption and low invertebrate consumption on Chalky Island compared with the other sites. The diet of male stoats was similar to that of female stoats on both Secretary Island and Resolution Island. Chalky Island male stoats were heavier than those on the other islands, while the females on the various islands had similar body weights. The variability in diet of stoats from these islands may in part reflect the temporal and spatial differences between the samples. However, it demonstrates the adaptability of stoats, and their ability to survive without mammalian prey in different ways. It supports the hypothesis that differences in body weights of stoats are at least partly driven by variation in prey size and/or availability.
... It is of note that in the Eglinton Valley, mean height of successful kaka nests was not significantly different from unsuccessful nests. Rather than nest height it was mean distance from the nearest trap that had a significant influence on whether a nest was successful or not, successful nests being closer to traps than unsuccessful nests (Dilks et al. 2003). Female kaka expended much effort to create a deep layer of friable, free-draining litter on which to nest. ...
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.
... Over the last 150 years, individual long-tailed bat colonies have potentially been through numerous bottlenecks as a result of periodic high levels of predation by introduced mammals, primarily ship rats (Rattus rattus) and stoats (Mustela erminea) (O'Donnell 2000b; Pryde et al. 2005). Both rat and stoat numbers irrupt in years following heavy fruiting of southern beech (Nothofagaceae), a dominant forest type in New Zealand, and in those years there is a significant decrease in survival of long-tailed bats and numerous hole-nesting bird species due to predation (O'Donnell 1996;Dilks et al. 2003;Pryde et al. 2005). This results in regular population crashes, from which the populations can only partially recover until the next predator outbreak reduces them even further. ...
Maintaining the genetic diversity of populations is important in conservation because it strongly influences the ability to adapt to changing environments. We characterised the genetic structure of the endemic and endangered New Zealand (NZ) long-tailed bat (Chalinolobus tuberculatus) in two valleys in Fiordland, NZ. Fiordland is one of the last strongholds of the species, which has drastically declined throughout NZ. C. tuberculatus has suffered from recent habitat fragmentation and episodic predation by exotic mammals over the last 150 years. Gene flow and structuring were measured using nine nuclear microsatellite loci. In addition, the hyper-variable domain HVI of the mitochondrial control region was sequenced to analyse population structure at the maternal level. Our results show that the nine colonies studied have retained high genetic diversity, with moderate signs of genetic bottlenecks. Furthermore, low F
ST and F
IS values indicated that all colonies are still connected by gene flow and do not show signs of inbreeding. Substantial gene flow among colonies was also demonstrated by Bayesian clustering and PCA analysis. At the mitochondrial level, substantial differentiation between colonies has resulted from strong natal philopatry in females. Overall, our results indicate that genetic diversity is maintained in the Fiordland population of C. tuberculatus despite regular population crashes and habitat fragmentation. Management should ensure that remaining habitat linkages are preserved and further predator-induced population bottlenecks are prevented so that current genetic diversity is maintained in the long-term.
... The main introduced predators of kaka (and other native birds) are stoats Mustela erminea, which kill adults (in particular females incubating eggs), brush-tailed possums Trichosurus Vulpecula, which rob nests and compete for high-energy foods and nest-sites, and rats (Rattus sp.), which prey on eggs and nestlings (Moorhouse et al. 2003; Heather and Robertson 2005). Pest control programs based on poisoning, trapping, and artificial physical barriers (e.g., to protect kaka nest cavities) have been applied to mitigate the impact caused by introduced mammals (Dilks et al. 2003; Greene and Jones 2003; Moorhouse et al. 2003; Veltman and Westbrook 2011). In Wellington city, the Karori Wildlife Sanctuary (now known as Zealandia) is a predator-free fenced area containing abundant native forest and connected to a green-belt surrounding the city (King 2005). ...
Urbanization and exotic species are major threats to the conservation of forest-dependent wildlife species. Some emblematic species, indicators of habitat quality for the conservation of other species, might successfully be reintroduced within cities when habitat restoration and pest management programs are combined. We studied the landscape resource selection of juvenile kaka Nestor meridionalis tracked with Global Positioning System (GPS) units and released into the predator-free reserve of Zealandia in Wellington city, New Zealand. Kaka moved beyond the predator exclusion fence into urban suburbs. The home range size and areas of high use estimated using local convex hull (a-LoCoH) ranged from 20 to 240 ha and 2 to 21 ha, respectively. Using resource selection functions and model selection we found that native forest patches and urban areas close to the reserve were selected by kaka to establish their home ranges. At a lower scale of selection (i.e., selection of habitats within home ranges), kaka selected the same habitat, but not necessarily those close to the reserve. Native forest patches throughout the city can facilitate the dispersal of individuals, while the reserve provides protection and opportunities for supplementary feeding. Urban areas might have been selected due to the placement of feeders in private backyards. Survival of forest-dwelling species in cities requires careful urban planning and management to provide the necessary habitat patches, refugia, and food sources.
... A range of mammals introduced to New Zealand prey on native forest birds, particularly on eggs, young and nesting adults, particularly during the breeding season (reviewed by Innes et al. 2010). Mammalian predators known to prey on birds in New Zealand include mustelids (Mustela spp., O'Donnell et al. 1996), rats (Rattus spp., Dilks et al. 2003), cats (Felis catus, Sanders and Maloney 2002), brushtail possums (Trichosurus vulpecula, Brown et al. 1993;Sadleir 2000) and hedgehogs (Erinaceus europaeus, Sanders and Maloney 2002). Possums and rodents also act as browsers and can reduce availability of food resources for birds (Payton 2000;Innes et al. 2010). ...
Context. Many conservation decisions rely on the assumption that multiple populations will respond similarly to management. However, few attempts have been made to evaluate correlated population responses to management or to identify traits that could be used to predict correlations. These assumptions are central to the use of the 'population indicator-species concept' (the idea that population trends of one species can be used as an index of trends in other species) for measuring the effects of key ecological drivers. Aims. We investigated correlations among bird population trends in a mixed podocarp-hardwood forest in New Zealand in which introduced mammalian pests are controlled. We analysed trends in the abundance of 18 bird species (primarily passerines) over a 10-year period, using data from 5-min bird counts. Methods. We used a Bayesian modelling approach to identify short-term correlations in population trends among species and to investigate whether ecological traits can be used to predict these correlated trends. Key results. Population increases were detected in 9 of the 18 bird species over the 10-year period of the study. Population trends were correlated for 10% of species pairs (of which 81% were positive correlations). Correlations among seven of the nine species that increased in abundance were always positive; these species form a potential indicator pool. However, traits were not useful for predicting correlated population trends. Conclusions. Bird species affected by a shared ecological driver (predation) can exhibit correlated population trends when introduced predators are controlled, but correlations cannot be predicted by similarity in ecological traits. Implications. We advocate for testing consistency of correlations at multiple sites so as to validate the evidence-based use of the population indicator-species concept as a cost-effective alternative to monitoring whole communities.
... Results of this 10-year study showed that apparent survival was significantly lower in years when the number of introduced mammalian predators was high and in years when the winter temperature was warmer than average (Pryde et al. 2005). Relative abundances of introduced predators were determined using a footprint tracking index (Gillies & Williams 2001) and kill-trapping (Dilks et al. 2003). High tracking indices for ship rats (Rattus rattus) were recorded in the forests during 3 of the 10 years of the study. ...
The survival of New Zealand long‐tailed bats (Chalinolobus tuberculatus) was assessed in two populations, one at Hanging Rock, South Canterbury, South Island, the other at Grand Canyon, central west North Island. Apparent survival of adult females over winter was calculated using mark‐recapture analysis over 5 years. Annual survival varied from 0.75 (95% CI = 0.54–0.88) to 0.89 (0.48–0.99) at Hanging Rock and 0.55 (0.39–0.71) to 0.91 (0.44–0.99) at Grand Canyon. Estimates of apparent survival were consistent with those from a longer‐term study of long‐tailed bats in the Eglinton Valley, Fiordland, South Island. The intrinsic rate of increase (λ) at Hanging Rock was 0.90 (95% CI = 0.4–0.99), indicating that this population may be declining more rapidly than that in the Eglinton Valley. At Grand Canyon, population estimates fluctuated annually, with no clear trend. Predation by introduced mammals and loss of habitat likely caused declines at Hanging Rock. Management of these factors is essential to avoid the local extinction of the species. Long‐term monitoring (greater than 5 years) is required to determine more robust population trends for these long‐tailed bat populations.
... For example, up until the 1990s, long-tailed bats were considered 'common and widespread' (Daniel & Williams 1984;Daniel 1990 Similarly, more intensive monitoring of single species has repeatedly demonstrated that new or previously unanticipated threats are found periodically, and that they would go undetected without longer-term monitoring programmes. For example, the impact of rats on the viability of mōhua (Dilks et al. 2003) or the influences of competition with wasps (Vespula vulgaris) and brushtail possums (Trichosurus vulpecula) on food availability for kākā . ...
... The benefits of effective predator control programmes have also now been documented, although primarily for forest birds (e.g. Basse et al. 2003;Dilks et al. 2003;Baber et al. 2009;Innes et al. 2010), but also see Cruz et al. (2013) for braided river birds and Reardon et al. (2012) for lizards. However, the potential impacts of these predators on freshwater birds in wetlands remain uncertain despite the significance of this habitat type in New Zealand (Williams 2004) and the extensive declines in the range and abundance of many freshwater birds since occupation of New Zealand by humans (Travers 1868;Potts 1869;Buller 1874;Hutchinson 1900;Hope 1927;Stead 1927;Oliver 1955;Tennyson & Martinson 2006). ...
Abstract: The impacts of introduced mammalian predators on the viability of bird populations in forest, river
and coastal habitats in New Zealand are well known. However, a common understanding of their impacts in
freshwater wetlands is lacking. We review evidence for impacts of introduced mammalian predators on freshwater
birds, particularly specialist species restricted to wetlands, and use this information to make predictions about
freshwater species likely to be vulnerable to predation. Extinctions and significant declines of freshwater species
have been numerous since humans introduced mammalian predators to New Zealand. Anecdotal evidence
links predation to the loss of 11 of 14 extinct birds that would have inhabited wetlands. Thirty extant species,
particularly ground-nesting species, are still under threat from mammalian predators. All introduced mammalian
predator species are abundant and/or widespread in New Zealand wetlands and most have been confirmed to
prey upon freshwater bird species. While their precise impacts on the long-term viability of threatened bird
populations have not been evaluated, evidence suggests that predation is a serious threat, warranting predator
control. An evaluation using documented predation events and ecological traits suggests that six threatened
wetland specialists are at high risk of predation: Australasian bittern (Botaurus poiciloptilus), banded rail
(Gallirallus philippensis), brown teal (Anas chlorotis), fernbird (Bowdleria punctata), marsh crake (Porzana
pusilla), and spotless crake (P. tabuensis). Research is needed on the ecology and behaviour of mammalian
predators in wetlands to help understand their impacts on long-term viability of bird populations and to assist
in developing and monitoring predator control programmes.
Article 7: Biodiversity Conservation & Management Studies in New Zealand Author: Liu Huan(1983-), Master of Science (First Class Honours), The University of Auckland.
Invasive mammalian predators are implicated in the ongoing decline of a suite of fauna and continue to be a major cause of human–wildlife conflict globally. Lethal control of invasive predators is a common management strategy; however, the use of activity indices to measure management effectiveness is problematic. Non‐invasive genetic sampling may be a viable alternative approach to monitoring as individual animals can be identified, allowing for direct estimation of population density through newly developed spatially explicit capture–recapture techniques. Here we compare inferences derived from a basic activity index (number of scats per survey) and genetic sampling of scats within a before–after control–impact design to evaluate the effectiveness of a lethal control programme targeting red foxes (Vulpes vulpes) in south‐eastern Australia. The activity index was highly variable through time and suggested the baiting programme reduced fox activity on the treatment transect relative to changes on the non‐treatment transect. In contrast, genetic sampling and spatially explicit capture–recapture analysis suggested fox density varied little throughout the study, with any changes unable to be attributed to the baiting programme. Additionally, genetic sampling confirmed many individuals persisted through 7 months of baiting. These contrasting results may be partially explained by changes in scat detectability due to seasonal changes in behaviour and the disproportionate contribution of some individuals to scat counts. Our pre‐baiting density estimate of 0.28 foxes km2 (95% CI: 0.22–0.38) was lower than expected given the high productivity, abundant prey species and lack of larger predators in the study region. Our results highlight the need for cautious interpretation of activity indices and demonstrates the value of incorporating recent methodological and statistical advances when evaluating lethal control programmes.
1. There is a global need for observation systems that deliver regular, timely data on state and trends in biodiversity, but few have been implemented, and fewer still at national scales. We describe the implementation of measurement of Essential Biodiversity Variables (EBVs) on an 8 km × 8 km grid throughout New Zealand, with multiple components of biodiversity (vegetation, birds, and some introduced mammals) measured simultaneously at each sample point.
2. Between 2011 and 2017, all public land was sampled nationally (ca. 1,350 points) and some private land (ca. 500 points). Synthetic appraisals of the state of New Zealand's biodiversity, not possible previously, can be derived from the first measurement of species distribution, population abundance, and taxonomic diversity EBVs.
3. Native bird counts (all species combined) were about 2.5 times greater per sample point in natural forests and shrublands than in non‐woody ecosystems, and native bird counts exceeded those of non‐native birds across all natural forests and shrublands.
4. Non‐native plants, birds, and mammals are invasive throughout, but high‐rainfall forested regions are least invaded, and historically deforested rain shadow regions are most invaded.
5. National reporting of terrestrial biodiversity across New Zealand's public land is established and becoming normalised, in the same manner as national and international reporting of human health and education statistics. The challenge is extending coverage across all private land. Repeated measurements of these EBVs, which began in 2017, will allow defensible estimates of biodiversity trends.
Acute, short-term effects of early-life stress and associated glucocorticoid upregulation on behavior are widely documented across vertebrates. However, the persistence and severity of these effects are largely unknown, especially through the adult stage and in wild species. Here, we investigate long-term effects of experimental post-natal increases in a circulating glucocorticoid on antipredator behavior in wild house sparrows (Passer domesticus) tested in captivity. We manipulate circulating corticosterone concentration in wild, free-living nestlings, transfer fledglings to captivity, and test juveniles and adults for two measures of antipredator behavior: evasiveness during a direct human encounter, and propensity to escape from a risky environment. We find no effect of early-life stress hormone manipulation on escape behavior, but a delayed effect on evasive behavior: evasive behavior was depressed in adults but not juveniles, and influenced by current body condition. These results highlight the importance of state-behavior interactions and life stage in assessing long-term effects of early-life stress, and provide rare evidence for delayed effects of early-life stress to adults of a wild avian species.
Mohua are endemic to the South Island of New Zealand but they have declined in both range and abundance. The causes of decline include predation from introduced predators and forest clearance. Mohua have survived in reasonable numbers in the Dart Valley in west Otago. In this paper we describe the relationship between the presence of mohua breeding territories and vegetation at a 1 ha scale within low altitude, red beech-dominated forest. The extent of shrub or regeneration was found to have the strongest association with the presence/absence of breeding mohua. Other factors which increase leaf volume, such as forest-edge and broken canopy were also important in explaining the presence of mohua. Milling was found to have a long lasting negative impact (>70 years) on mohua presence. Management which reduces grazing and increases the shrub and regeneration forest component is likely to increase mohua carrying capacity.
The Chatham Islands tomtit (Petroica macrocephala chathamensis) is a small forest passerine with a threat ranking of nationally endangered.It is restricted to 2 islands of the Chathams group that are free of introduced predators (Rangatira and Mangere Islands), and 1 with mice (Mus musculus) and feral cats (Felis catus) (Pitt Island).We carried out a translocation of 35 juvenile tomtits from Rangatira (10 male, 10 female) and Pitt Islands (6 male, 9 female) to Awatotara Valley, Chatham Island in January 2011.Mean weight at capture of Pitt Island tomtits was lighter than that of the Rangatira Island tomtits.Tomtits were held captive in aviaries for 1-3 days on the source islands and 2-4 days at the release site.Weight loss of tomtits in captivity prior to transfer averaged 1.8% of body mass per day held and was more pronounced in birds sourced from Rangatira than Pitt Island.Two birds died during the first night after transfer, but the other 33 were released in apparently good health.Eighteen of the released birds were seen at least once, and 11 regularly until 28 March (at least 55 days after release).During the following 12 days, all 11 of these tomtits disappeared.We discuss possible reasons for their disappearance, and aspects of the translocation that may be useful for future translocations of tomtits and other species with a similar ecology.
New Zealand was one of the last land masses to be populated by humans, and its isolation has contributed to the large number of endemic species that the country is known for. With increased global movement of people and goods this historic advantage no longer exists. In the last several decades numerous legislative, policy and operational tools have been used to protect New Zealand’s special areas and biota from invasive alien species. With the benefit of 25 years of dedicated protection efforts by the Department of Conservation, best practice alien plant control techniques have been developed, building on lessons from animal pest eradications, trophic relationships, and on-the ground pragmatism and experience. Increasingly, an essential tool to achieving greater success will be working with other agencies, businesses and communities to harness resources. Three case studies illustrate the approaches and lessons learnt from alien plant management in New Zealand in the last 25 years: Raoul Island in the far north of New Zealand, Hen and Chicken Islands to the east of North Auckland Peninsula, and Fiordland National Park in south-western South Island.
Incremental lines in the canine teeth of 20 stoats (Mustela erminea) corresponded exactly with known age in 5 males and 7 females marked as young, and with minimum-known age in 6 males and 2 females marked as adults. The lines are added in autumn (April and May) of each year, beginning when the animals are 6 months old. The correlation is accurate enough to permit determination of the ages of wild-caught adult stoats of unknown age. Two other techniques used previously (baculum weight, post-orbital ratio of the skull) are confirmed as accurate but much less precise methods of distinguishing young from adult stoats.
Breeding Mohua (Yellowhead, Mohoua ochrocephala; Passerifones) have been intensively monitored in the Eglinton Valley, Fiordland, since 1990. Birds were individually colour-banded and their territories mapped. Trapping and poisoning stoats (Mustela e n i n e a) resulted in a large increase in Mohua numbers, but the population declined abruptly in winter 1996 following a period of unusually low temperatures. Details of the increase in numbers are presented and the reasons for the subsequent sharp population decline are discussed.
The home range of stoats (Mustela erminea) was
determined as part of a programme to protect Okarito brown kiwi chicks
(Apteryx australis) ‘Okarito’, from
predation. Twenty-seven stoats were fitted with radio-transmitters and tracked
in two podocarp (Podocarpaceae) forests, in south Westland, New Zealand, from
July 1997 to May 1998. Home-range area was determined for 19 animals by
minimum convex polygons and restricted-edge polygons, and core areas were
determined by hierarchical cluster analysis. The mean home ranges of males
across all seasons calculated by minimum convex polygon (210 28 ha ( s.e.))
and restricted-edge polygon (176 29 ha) were significantly larger than those
of females across all seasons (89 14 ha and 82 12 ha). The mean home range of
males calculated by minimum convex polygon during the breeding season (256 38
ha) was significantly larger than the mean home range pooled across the
non-breeding seasons (149 16 ha), whereas that calculated by restricted-edge
polygon was not significantly different. The mean home range of females during
the breeding season was not significantly different from that in the
non-breeding seasons when estimated by either method. Overlap of home ranges
was observed within and between sexes in all seasons, with the greatest
proportion of home range overlap being male–female. The mean home range
of females in spring and summer is used to guide the spacing of control
stations.
Home range and diet of stoats inhabiting beech forest were examined by trapping and radio-tracking. Eleven stoats (6 female, 5 male) were fitted with radio-transmitters. Minimum home ranges of five females averaged 124 ± 21 ha and of four males 206 ± 73 ha. Range lengths of females averaged 2.3 ± 0.3 km and of males 4.0 ± 0.9 km. These differences were not statistically significant. Adult female stoats appeared to have mutually exclusive home ranges. Two females and one male had home ranges that were bisected by the Eglinton River. All three crossed the river regularly and could only have done so by swimming. Bird remains were found in 54% of stoat guts and scats examined, lagomorphs in 33%, and invertebrates in 34%. Australian brushtail possum remains were found in 11% of samples overall, but only in guts and scats from male stoats. A road through the study area affected the behaviour of stoats. Females avoided the road but males preferred it and were found scavenging road-kills, which may explain why they are more frequently found as road-kills themselves. In most years, New Zealand beech forest may be marginal habitat for stoats. No breeding was detected in the year of our study but there had been high productivity in the previous season. Stoats probably survive in this habitat because they are flexible in their diet and because their breeding biology allows them to respond rapidly to a sudden increase in food availability.
This radio-tracking study reports the spring home range, spatial organisation and activity of 11 stoats Mustela erminea in a New Zealand Nothofagus forest, 1,5 yr after significant seedfall when rodent density was low, but stoat density was high. The average home range of 4 male stoats was 223 (SE = 45) ha, significantly larger than the average range area of 94 (SE = 13) ha recorded for 7 female stoats. Stoats were generally tolerant of sharing space and did not maintain intra- or intersexual territorial spacing systems. There was no evidence of temporal avoidance with several stoats of the same sex showing slight attraction to one another. However, stoats still may avoid one another when in close proximity. Long-term radio-tracking studies are required to determine the general patterns of spacing behaviour in stoats, Male stoats showed higher levels of activity during daylight than females.
Mist netting techniques - a method using telescopic aluminium poles
- P J Dilks
- G P Elliott
- C F J Donnell
Dilks, P.J.; Elliott, G.P.; O’Donnell, C.F.J. 1995. Mist netting techniques - a method using telescopic aluminium poles. Ecological Management 3: 20- 28. Department of Conservation, Wellington
Checklist of birds of New Zealand, Third edition
- E G Turbott
Turbott, E.G. 1990. Checklist of birds of New Zealand, Third edition. Random Century, Auckland, N.Z