Is habitat enhancement a viable strategy for conserving New Zealand's endemic lizards?

<p>In our current era, the Anthropocene, species are disappearing at an unprecedented rate due to the impact of humans on Earth’s environments. Of the many causes of these extinctions, habitat loss is thought to be the most severe. Three habitat management strategies are available for halting habitat loss: reservation, restoration and reconciliation. The latter two of these strategies actively seek to improve the ability of degraded or lost habitats to support species. If successful on a large enough scale, use of restoration and reconciliation (hereafter referred to collectively as ‘habitat enhancement’) could reverse the effects of habitat loss. I evaluated the viability of habitat enhancement for the conservation of New Zealand’s lizard fauna. 83% of New Zealand’s 106+ endemic species are threatened or at risk of extinction. While habitat loss is one key driver of declines, predation by invasive mammals is the other. Neither of these processes are well understood. Habitat enhancement is increasingly being employed in New Zealand by landowners, community groups, conservationists, and businesses as a strategy for mitigating lizard declines, but outcomes are rarely investigated comprehensively. This is concerning because habitat manipulation potentially affects both exotic and native species, which has led to unexpected negative effects on threatened fauna in New Zealand and overseas. I posed four questions to help address this knowledge gap. (1) What habitat enhancement strategies are available for reptiles, and have they produced successful conservation outcomes? (2) How do habitat characteristics affect populations and communities of endemic New Zealand lizards? (3) How does the presence of invasive mammals affect populations and communities of endemic New Zealand lizards over intermediate to long-term time frames? (4) Can habitat enhancement produce positive conservation outcomes in the presence of invasive mammals? A review of the global literature on habitat enhancement for reptiles identified 75 studies documenting 577 responses of 251 reptile species. For outcome evaluation, I adapted an existing stage-based framework for assessment of translocation success. High levels of success (84-85%) at Stages 1 (use of enhanced habitat) and 2 (evidence of reproduction in enhanced habitat) suggested that enhancement could be useful for creating areas that can be inhabited, and reproduced in, by reptiles. Fewer cases were successful at Stage 3 (30%; improvement of at least one demographic parameter demonstrated in enhanced habitat) or Stage 4 (43%; self-sustaining or source population established in enhanced habitat). Additionally, only 1% of the 577 cases sufficiently examined or modelled long-term population trends to allow evaluation against the Stage 4 criterion. Thus, there was a lack of evidence indicating that enhancement could result in higher population growth rates, or reduced extinction risk, of reptiles. I conducted field work in the Wellington region to investigate the effects of habitat characteristics and mammals on terrestrial lizards inhabiting coastal environments. Surveys conducted in two mammal-invaded mainland areas and on two mammal-free offshore islands showed that presence or absence of invasive mammals had a stronger effect on lizard community structure than habitat variables. However, occupancy probabilities of northern grass skinks Oligosoma polychroma and Raukawa geckos Woodworthia maculata were positively correlated with increasing cover of divaricating shrubs. O. polychroma were also more likely to occupy patches with increasing cover by non-Muehlenbeckia vines. Mark-recapture studies were conducted at two mammal-invaded mainland sites to investigate the current abundance of lizard species: Turakirae Head and Pukerua Bay. Estimated densities of O. polychroma ranged between 3,980 and 4,078 individuals / ha and W. maculata between 4,067 and 38,372 individuals / ha. Other species known to occur, at least historically, at each site were either not detected or comprised only a small proportion of total lizard captures. Analysis of longitudinal lizard monitoring data available for Pukerua Bay, Turakirae Head, and an additional mammal-invaded site, Baring Head, did not reveal a significant decline in abundance, occupancy, or catch rates of O. polychroma over time periods ranging between six and 34 years, nor of W. maculata over six to 49 years. Habitat information available for Baring Head showed that the probability of local extinction of W. maculata was significantly lower at rocky sites. Finally, I conducted a before-after-control-impact habitat enhancement experiment on lizard communities inhabiting 100 m2 plots on the mammal-invaded Miramar Peninsula. After a six-month pre-enhancement monitoring period, native plants and gravel piles were added to enhancement plots and lizard monitoring continued for a further nine months. Enhancement did not significantly affect plot use, body condition, or evidence of reproduction in Oligosoma aeneum, O. polychroma or W. maculata, but were considered successful at Stages 1 and 2 due to the absence of a negative effect. Neither the abundance, probability of entry into plots by birth or immigration, nor apparent survival of O. aeneum was significantly affected by enhancement (Stage 3). Apparent survival of O. polychroma increased significantly in response to enhancement, but this did not result in increased abundance. Adding gravel and native vegetation (especially divaricating shrubs and vines) may be a suitable strategy for creating habitat in invaded coastal landscapes for O. polychroma and W. maculata. However, most of the other lizard species that would have historically occurred in mammal-invaded coastal areas of Wellington appeared to be sensitive to sustained mammal presence, even with low-to-moderate levels of control in operation. Therefore, habitat enhancement without intensive mammal control or eradication is not expected to benefit these species, nor be capable of restoring coastal lizard communities. In invaded landscapes it is, at best, a reconciliation measure that could allow co-existence of an endemic lizard community comprised of common species with invasive mammals. However, habitat enhancement could still be useful for restoring lizard communities in mammal-free sanctuaries.</p>

Is habitat enhancement a viable strategy for conserving New Zealand's endemic lizards?

<p>In our current era, the Anthropocene, species are disappearing at an unprecedented rate due to the impact of humans on Earth’s environments. Of the many causes of these extinctions, habitat loss is thought to be the most severe. Three habitat management strategies are available for halting habitat loss: reservation, restoration and reconciliation. The latter two of these strategies actively seek to improve the ability of degraded or lost habitats to support species. If successful on a large enough scale, use of restoration and reconciliation (hereafter referred to collectively as ‘habitat enhancement’) could reverse the effects of habitat loss. I evaluated the viability of habitat enhancement for the conservation of New Zealand’s lizard fauna. 83% of New Zealand’s 106+ endemic species are threatened or at risk of extinction. While habitat loss is one key driver of declines, predation by invasive mammals is the other. Neither of these processes are well understood. Habitat enhancement is increasingly being employed in New Zealand by landowners, community groups, conservationists, and businesses as a strategy for mitigating lizard declines, but outcomes are rarely investigated comprehensively. This is concerning because habitat manipulation potentially affects both exotic and native species, which has led to unexpected negative effects on threatened fauna in New Zealand and overseas. I posed four questions to help address this knowledge gap. (1) What habitat enhancement strategies are available for reptiles, and have they produced successful conservation outcomes? (2) How do habitat characteristics affect populations and communities of endemic New Zealand lizards? (3) How does the presence of invasive mammals affect populations and communities of endemic New Zealand lizards over intermediate to long-term time frames? (4) Can habitat enhancement produce positive conservation outcomes in the presence of invasive mammals? A review of the global literature on habitat enhancement for reptiles identified 75 studies documenting 577 responses of 251 reptile species. For outcome evaluation, I adapted an existing stage-based framework for assessment of translocation success. High levels of success (84-85%) at Stages 1 (use of enhanced habitat) and 2 (evidence of reproduction in enhanced habitat) suggested that enhancement could be useful for creating areas that can be inhabited, and reproduced in, by reptiles. Fewer cases were successful at Stage 3 (30%; improvement of at least one demographic parameter demonstrated in enhanced habitat) or Stage 4 (43%; self-sustaining or source population established in enhanced habitat). Additionally, only 1% of the 577 cases sufficiently examined or modelled long-term population trends to allow evaluation against the Stage 4 criterion. Thus, there was a lack of evidence indicating that enhancement could result in higher population growth rates, or reduced extinction risk, of reptiles. I conducted field work in the Wellington region to investigate the effects of habitat characteristics and mammals on terrestrial lizards inhabiting coastal environments. Surveys conducted in two mammal-invaded mainland areas and on two mammal-free offshore islands showed that presence or absence of invasive mammals had a stronger effect on lizard community structure than habitat variables. However, occupancy probabilities of northern grass skinks Oligosoma polychroma and Raukawa geckos Woodworthia maculata were positively correlated with increasing cover of divaricating shrubs. O. polychroma were also more likely to occupy patches with increasing cover by non-Muehlenbeckia vines. Mark-recapture studies were conducted at two mammal-invaded mainland sites to investigate the current abundance of lizard species: Turakirae Head and Pukerua Bay. Estimated densities of O. polychroma ranged between 3,980 and 4,078 individuals / ha and W. maculata between 4,067 and 38,372 individuals / ha. Other species known to occur, at least historically, at each site were either not detected or comprised only a small proportion of total lizard captures. Analysis of longitudinal lizard monitoring data available for Pukerua Bay, Turakirae Head, and an additional mammal-invaded site, Baring Head, did not reveal a significant decline in abundance, occupancy, or catch rates of O. polychroma over time periods ranging between six and 34 years, nor of W. maculata over six to 49 years. Habitat information available for Baring Head showed that the probability of local extinction of W. maculata was significantly lower at rocky sites. Finally, I conducted a before-after-control-impact habitat enhancement experiment on lizard communities inhabiting 100 m2 plots on the mammal-invaded Miramar Peninsula. After a six-month pre-enhancement monitoring period, native plants and gravel piles were added to enhancement plots and lizard monitoring continued for a further nine months. Enhancement did not significantly affect plot use, body condition, or evidence of reproduction in Oligosoma aeneum, O. polychroma or W. maculata, but were considered successful at Stages 1 and 2 due to the absence of a negative effect. Neither the abundance, probability of entry into plots by birth or immigration, nor apparent survival of O. aeneum was significantly affected by enhancement (Stage 3). Apparent survival of O. polychroma increased significantly in response to enhancement, but this did not result in increased abundance. Adding gravel and native vegetation (especially divaricating shrubs and vines) may be a suitable strategy for creating habitat in invaded coastal landscapes for O. polychroma and W. maculata. However, most of the other lizard species that would have historically occurred in mammal-invaded coastal areas of Wellington appeared to be sensitive to sustained mammal presence, even with low-to-moderate levels of control in operation. Therefore, habitat enhancement without intensive mammal control or eradication is not expected to benefit these species, nor be capable of restoring coastal lizard communities. In invaded landscapes it is, at best, a reconciliation measure that could allow co-existence of an endemic lizard community comprised of common species with invasive mammals. However, habitat enhancement could still be useful for restoring lizard communities in mammal-free sanctuaries.</p>

Understanding distributions of invasive mammals in urban environments using remote cameras and citizen science

<p>Preserving biodiversity in urban environments is crucial not only for preventing local extinctions of native species, but also for educating the public about the importance of species conservation. Invasive mammalian species can have negative impacts for both people and biodiversity in urban environments. Understanding the factors influencing the distribution of these invasive species is crucial to comply with the ethical, ecological, and practical concerns associated with their management. Remote cameras are an increasingly popular tool for investigating the distribution and abundance of mammals. Yet few studies have used these cameras in urban environments. The time and effort required to classify remote camera data is the main constraint of this monitoring technique. To determine whether employing citizen science could facilitate the use of remote cameras in urban environments, I investigated the engagement, accuracy, and efficiency of volunteers (i.e., citizen scientists) in classifying animal images recorded by remote cameras in Wellington, New Zealand. Classifications from citizen scientists were in 84.2% agreement with classifications of expert ecologists. However, accuracy varied significantly among species and volunteers. Aggregating multiple classifications per image and highlighting animal movement in the images improved the accuracy of citizen scientists. Additionally, weighting their classifications based on previous accuracy, self-assessed confidence, and the species reported reduced the number of volunteer classifications required to achieve levels of accuracy comparable to that of experts. These results illustrate that citizen science allows for accurate and efficient classifications of remote camera data from urban areas. Using the classifications provided by citizen scientists, I then evaluated the suitability of remote cameras to monitor invasive mammals in urban environments. Based on data collected from forest and residential areas of Wellington, New Zealand, remote cameras detected significantly more European hedgehogs (Erinaceus europaeus) and rats (Rattus spp.) than tracking tunnels. Cameras, however, missed recording house mice (Mus musculus) on some occasions where tracking tunnels detected them, and vice-versa. Overall, my results demonstrate that remote cameras are a more efficient multi-species monitoring tool than tracking tunnels. Independent of habitat type, cats (Felis catus), hedgehogs, and mice were the species most frequently recorded. Data from remote cameras subsequently helped quantify differences in the occupancy rates of species between residential and forested areas furthering our ecological understanding of the distribution of invasive species in peopled landscapes. To identify the underlying processes influencing the distribution and abundances of invasive mammals found in urban patches of vegetation, I also used remote cameras to investigate the influence of habitat quality, management efforts, interspecific interactions and seasonality on the occupancy and relative abundance of invasive mammals in 47 patches of forest within Wellington. My results indicate that distance to forest edge influences positively on the relative abundance of rodents and negatively on the relative abundance of common brushtail possums (Trichosurus vulpecula), cats, European rabbits (Oryctolagus cuniculus), and hedgehogs. The cameras also revealed a positive interaction between the occupancy of ship rats (Rattus rattus) and the abundance of Norway rats (Rattus norvegicus), a positive influence of the nearby buildings on the occupancy of cats, and how management control reduces the occupancy of target species, particularly during spring. These results illustrate the importance of using season- and species-specific approaches to identify the most important factors influencing the distribution of invasive species in urban environments. Overall, my research highlights the benefits of engaging the public with scientific research, the advantages of using remote cameras to monitor mammals in urban environments and the importance of controlling invasive species at adequate spatial and temporal scales to ensure effective conservation management.</p>

Understanding distributions of invasive mammals in urban environments using remote cameras and citizen science

<p>Preserving biodiversity in urban environments is crucial not only for preventing local extinctions of native species, but also for educating the public about the importance of species conservation. Invasive mammalian species can have negative impacts for both people and biodiversity in urban environments. Understanding the factors influencing the distribution of these invasive species is crucial to comply with the ethical, ecological, and practical concerns associated with their management. Remote cameras are an increasingly popular tool for investigating the distribution and abundance of mammals. Yet few studies have used these cameras in urban environments. The time and effort required to classify remote camera data is the main constraint of this monitoring technique. To determine whether employing citizen science could facilitate the use of remote cameras in urban environments, I investigated the engagement, accuracy, and efficiency of volunteers (i.e., citizen scientists) in classifying animal images recorded by remote cameras in Wellington, New Zealand. Classifications from citizen scientists were in 84.2% agreement with classifications of expert ecologists. However, accuracy varied significantly among species and volunteers. Aggregating multiple classifications per image and highlighting animal movement in the images improved the accuracy of citizen scientists. Additionally, weighting their classifications based on previous accuracy, self-assessed confidence, and the species reported reduced the number of volunteer classifications required to achieve levels of accuracy comparable to that of experts. These results illustrate that citizen science allows for accurate and efficient classifications of remote camera data from urban areas. Using the classifications provided by citizen scientists, I then evaluated the suitability of remote cameras to monitor invasive mammals in urban environments. Based on data collected from forest and residential areas of Wellington, New Zealand, remote cameras detected significantly more European hedgehogs (Erinaceus europaeus) and rats (Rattus spp.) than tracking tunnels. Cameras, however, missed recording house mice (Mus musculus) on some occasions where tracking tunnels detected them, and vice-versa. Overall, my results demonstrate that remote cameras are a more efficient multi-species monitoring tool than tracking tunnels. Independent of habitat type, cats (Felis catus), hedgehogs, and mice were the species most frequently recorded. Data from remote cameras subsequently helped quantify differences in the occupancy rates of species between residential and forested areas furthering our ecological understanding of the distribution of invasive species in peopled landscapes. To identify the underlying processes influencing the distribution and abundances of invasive mammals found in urban patches of vegetation, I also used remote cameras to investigate the influence of habitat quality, management efforts, interspecific interactions and seasonality on the occupancy and relative abundance of invasive mammals in 47 patches of forest within Wellington. My results indicate that distance to forest edge influences positively on the relative abundance of rodents and negatively on the relative abundance of common brushtail possums (Trichosurus vulpecula), cats, European rabbits (Oryctolagus cuniculus), and hedgehogs. The cameras also revealed a positive interaction between the occupancy of ship rats (Rattus rattus) and the abundance of Norway rats (Rattus norvegicus), a positive influence of the nearby buildings on the occupancy of cats, and how management control reduces the occupancy of target species, particularly during spring. These results illustrate the importance of using season- and species-specific approaches to identify the most important factors influencing the distribution of invasive species in urban environments. Overall, my research highlights the benefits of engaging the public with scientific research, the advantages of using remote cameras to monitor mammals in urban environments and the importance of controlling invasive species at adequate spatial and temporal scales to ensure effective conservation management.</p>

Do Invasive Mammal Eradications from Islands Support Climate Change Adaptation and Mitigation?

Climate change represents a planetary emergency that is exacerbating the loss of native biodiversity. In response, efforts promoting climate change adaptation strategies that improve ecosystem resilience and/or mitigate climate impacts are paramount. Invasive Alien Species are a key threat to islands globally, where strategies such as preventing establishment (biosecurity), and eradication, especially invasive mammals, have proven effective for reducing native biodiversity loss and can also advance ecosystem resilience and create refugia for native species at risk from climate change. Furthermore, there is growing evidence that successful eradications may also contribute to mitigating climate change. Given the cross-sector potential for eradications to reduce climate impacts alongside native biodiversity conservation, we sought to understand when conservation managers and funders explicitly sought to use or fund the eradication of invasive mammals from islands to achieve positive climate outcomes. To provide context, we first summarized available literature of the synergistic relationship between invasive species and climate change, including case studies where invasive mammal eradications served to meet climate adaptation or mitigation solutions. Second, we conducted a systematic review of the literature and eradication-related conference proceedings to identify when these synergistic effects of climate and invasive species were explicitly addressed through eradication practices. Third, we reviewed projects from four large funding entities known to support climate change solutions and/or native biodiversity conservation efforts and identified when eradications were funded in a climate change context. The combined results of our case study summary paired with systematic reviews found that, although eradicating invasive mammals from islands is an effective climate adaptation strategy, island eradications are poorly represented within the climate change adaptation and mitigation funding framework. We believe this is a lost opportunity and encourage eradication practitioners and funders of climate change adaptation to leverage this extremely effective nature-based tool into positive conservation and climate resilience solutions.

The responses of New Zealand's arboreal forest birds to invasive mammal control

<p>Introduced mammalian predators are responsible for over half of contemporary extinctions and declines of birds. Endemic bird species on islands are particularly vulnerable to invasions of mammalian predators. The native bird species that remain in New Zealand forests continue to be threatened by predation from invasive mammals, with brushtail possums (Trichosurus vulpecula) ship rats (Rattus rattus) and stoats (Mustela erminea) identified as the primary agents responsible for their ongoing decline. Extensive efforts to suppress these pests across New Zealand’s forests have created "management experiments" with potential to provide insights into the ecological forces structuring forest bird communities. To understand the effects of invasive mammals on birds, I studied responses of New Zealand bird species at different temporal and spatial scales to different intensities of control and residual densities of mammals. In my first empirical chapter (Chapter 2), I present two meta-analyses of bird responses to invasive mammal control. I collate data from biodiversity projects across New Zealand where long-term monitoring of arboreal bird species was undertaken. The projects cover a range of treatments including fenced sanctuaries, offshore islands, forests treated periodically and sites lacking significant mammal control. I found that New Zealand bird species exhibit complex responses to the varied and sustained management effort that has occurred across New Zealand’s landscape in the last fifty years. Some species show significant positive outcomes to control, notably the larger endemic species, while others, including highly endemic species, consistently decline after control. In Chapter 3, I estimate the responses of bird populations in the central New Zealand region to changes in ship rat densities. I collaborated with scientists from the Department of Conservation (DOC) and Greater Wellington Regional Council and collated biodiversity data from four restoration projects located across the central New Zealand region. I constructed multiple density impact functions (DIFs), where the effect of a change in density of a pest on a valued resource is quantified, to describe the impacts of ship rat population dynamics on native bird populations. These responses were then modelled in a meta-analysis to provide overall effects for bird populations when rat abundance increases. I identified two taxa that exhibit significant negative responses across the region: the native parakeet species (Cyanoramphus spp.) and the tomtit (Petroica macrocephala). Evidence from single projects also showed that two other species were negatively affected by increases in rats: the South Island kaka (Nestor meridionalis) and the North Island rifleman (Acanthisitta chloris). Conversely, populations of the recently introduced silvereye (Zosterops lateralis) were resilient to rat population recovery as silvereye counts significantly increased the year after an increase in ship rat populations was observed. In Chapter 4, I monitored bird species through a 1080 mammal-control operation in the southern Wairarapa. This operation coincided with a heavy beech mast, an irruptive event that occurs every 2-6 years. Most likely because of the abundance of seed, suppression of ship rats and possums appeared to be short-lived, and detections of these two mammals returned to pre-control levels within one and two years, respectively. Short-term responses of native birds to the control operation were positive: initially, for the small-medium sized bird species (i.e. the bellbird (Anthornis melanura), rifleman, tomtit, and tui (Prosthemadera novaeseelandiae) with a delayed positive response of the largest species 2.5 years after control (the New Zealand pigeon (Hemiphaga novaeseelandiae). In my final data chapter, I focus on the nesting outcomes of a common endemic species, the North Island fantail (Rhipidura fuliginosa placabilis), to different densities of ship rats. Through intensive monitoring of over 100 fantail nests, I estimated the outcomes of nesting attempts and formulated a DIF where nesting success was modelled as a function of the abundance of ship rats at the nest micro-site. Nesting attempts suffered higher failure rates at sites with higher rat abundance however, in this study I also identified a feature of nest placement that apparently limits predation from mammals. Nests placed on thinner branches were more likely to survive rat predation, a neat trick that perhaps only the smallest of birds can manage. My thesis identifies some species as particularly vulnerable to invasive mammalian predation while others are more resilient. Understanding resilience and vulnerability in New Zealand’s bird species sheds light on historical extinctions and the processes that continue to mould New Zealand's avifauna. I quantified responses of New Zealand forest bird species, to different levels of invasive mammal management and residual densities of mammals, with consideration of climate and forest productivity. These estimates could be applied by conservation managers to more effectively gauge future threats to native avifauna according to the attributes of bird species and present and future management scenarios.</p>

The responses of New Zealand's arboreal forest birds to invasive mammal control

<p>Introduced mammalian predators are responsible for over half of contemporary extinctions and declines of birds. Endemic bird species on islands are particularly vulnerable to invasions of mammalian predators. The native bird species that remain in New Zealand forests continue to be threatened by predation from invasive mammals, with brushtail possums (Trichosurus vulpecula) ship rats (Rattus rattus) and stoats (Mustela erminea) identified as the primary agents responsible for their ongoing decline. Extensive efforts to suppress these pests across New Zealand’s forests have created "management experiments" with potential to provide insights into the ecological forces structuring forest bird communities. To understand the effects of invasive mammals on birds, I studied responses of New Zealand bird species at different temporal and spatial scales to different intensities of control and residual densities of mammals. In my first empirical chapter (Chapter 2), I present two meta-analyses of bird responses to invasive mammal control. I collate data from biodiversity projects across New Zealand where long-term monitoring of arboreal bird species was undertaken. The projects cover a range of treatments including fenced sanctuaries, offshore islands, forests treated periodically and sites lacking significant mammal control. I found that New Zealand bird species exhibit complex responses to the varied and sustained management effort that has occurred across New Zealand’s landscape in the last fifty years. Some species show significant positive outcomes to control, notably the larger endemic species, while others, including highly endemic species, consistently decline after control. In Chapter 3, I estimate the responses of bird populations in the central New Zealand region to changes in ship rat densities. I collaborated with scientists from the Department of Conservation (DOC) and Greater Wellington Regional Council and collated biodiversity data from four restoration projects located across the central New Zealand region. I constructed multiple density impact functions (DIFs), where the effect of a change in density of a pest on a valued resource is quantified, to describe the impacts of ship rat population dynamics on native bird populations. These responses were then modelled in a meta-analysis to provide overall effects for bird populations when rat abundance increases. I identified two taxa that exhibit significant negative responses across the region: the native parakeet species (Cyanoramphus spp.) and the tomtit (Petroica macrocephala). Evidence from single projects also showed that two other species were negatively affected by increases in rats: the South Island kaka (Nestor meridionalis) and the North Island rifleman (Acanthisitta chloris). Conversely, populations of the recently introduced silvereye (Zosterops lateralis) were resilient to rat population recovery as silvereye counts significantly increased the year after an increase in ship rat populations was observed. In Chapter 4, I monitored bird species through a 1080 mammal-control operation in the southern Wairarapa. This operation coincided with a heavy beech mast, an irruptive event that occurs every 2-6 years. Most likely because of the abundance of seed, suppression of ship rats and possums appeared to be short-lived, and detections of these two mammals returned to pre-control levels within one and two years, respectively. Short-term responses of native birds to the control operation were positive: initially, for the small-medium sized bird species (i.e. the bellbird (Anthornis melanura), rifleman, tomtit, and tui (Prosthemadera novaeseelandiae) with a delayed positive response of the largest species 2.5 years after control (the New Zealand pigeon (Hemiphaga novaeseelandiae). In my final data chapter, I focus on the nesting outcomes of a common endemic species, the North Island fantail (Rhipidura fuliginosa placabilis), to different densities of ship rats. Through intensive monitoring of over 100 fantail nests, I estimated the outcomes of nesting attempts and formulated a DIF where nesting success was modelled as a function of the abundance of ship rats at the nest micro-site. Nesting attempts suffered higher failure rates at sites with higher rat abundance however, in this study I also identified a feature of nest placement that apparently limits predation from mammals. Nests placed on thinner branches were more likely to survive rat predation, a neat trick that perhaps only the smallest of birds can manage. My thesis identifies some species as particularly vulnerable to invasive mammalian predation while others are more resilient. Understanding resilience and vulnerability in New Zealand’s bird species sheds light on historical extinctions and the processes that continue to mould New Zealand's avifauna. I quantified responses of New Zealand forest bird species, to different levels of invasive mammal management and residual densities of mammals, with consideration of climate and forest productivity. These estimates could be applied by conservation managers to more effectively gauge future threats to native avifauna according to the attributes of bird species and present and future management scenarios.</p>

Novel Predators and Naïve Prey: How Introduced Mammals Shape Behaviours and Populations of New Zealand Lizards

<p>Biotas that evolved in isolation from mammalian predators are susceptible to degradation due to recent human-mediated introductions of mammals. However, behavioural, morphological and life historical adaptations of prey to novel mammalian predators can allow prey to persist in mammal-invaded areas. Lizards in New Zealand are an ideal group for exploring the effects of invasive mammals on vertebrate prey because: (1) the ca. 80 endemic species evolved without mammals as a major influence for 80 my, (2) mammalian introductions during the past 2000 y have differentially affected lizard species, and (3) some species coexist with mammals on the mainland as well as occurring on mammal-free offshore islands. I tested three hypotheses: (1) lizard populations that have persisted on New Zealand’s mainland are no longer declining in the presence of introduced mammalian predators, (2) introduced mammals induce behavioural shifts in native lizards, and (3) lizard behavioural patterns and chemosensory predator detection abilities vary according to exposure to introduced mammals. Trends in capture rates of five sympatric native lizard populations over a 23 year (1984-2006) period demonstrate that not all lizard populations that have persisted thus far on New Zealand’s mainland have stabilised in numbers. Large, nocturnal and terrestrial species remain highly vulnerable at mainland sites. Introduced kiore, Rattus exulans, induce behavioural changes in Duvaucel’s geckos, Hoplodactylus duvaucelii. A radio telemetric study demonstrated that geckos start reverting to natural use of habitats within six months of kiore eradication. Activity patterns of common geckos, H. maculatus, and common skinks, Oligosoma nigriplantare polychroma, in laboratory trials are also correlated with their exposure to mammalian predators. Lizard activity (time spent moving) increases relative to freeze behaviour with greater exposure to mammals. However, specific antipredator behaviours are not elicited by chemical cues of either native (tuatara, Sphenodon spp) or introduced (ship rat, R. rattus) predators. Lizard populations may persist by changing their behaviours in the presence of invasive mammals. However, the continued declines of particularly vulnerable mainland lizard taxa suggest that mammal-induced behavioural shifts may only slow population declines rather than enabling long-term survival. Eradicating pest mammals from offshore islands has proven effective at restoring both populations and behaviours of native lizards, but lizard populations on the mainland also deserve conservation priority. Research directed at understanding the synergistic effects of invasive species that are causing continued lizard population declines and mammal-proof fencing to protect the most vulnerable mainland populations from extinction are both urgently required.</p>

Novel Predators and Naïve Prey: How Introduced Mammals Shape Behaviours and Populations of New Zealand Lizards

<p>Biotas that evolved in isolation from mammalian predators are susceptible to degradation due to recent human-mediated introductions of mammals. However, behavioural, morphological and life historical adaptations of prey to novel mammalian predators can allow prey to persist in mammal-invaded areas. Lizards in New Zealand are an ideal group for exploring the effects of invasive mammals on vertebrate prey because: (1) the ca. 80 endemic species evolved without mammals as a major influence for 80 my, (2) mammalian introductions during the past 2000 y have differentially affected lizard species, and (3) some species coexist with mammals on the mainland as well as occurring on mammal-free offshore islands. I tested three hypotheses: (1) lizard populations that have persisted on New Zealand’s mainland are no longer declining in the presence of introduced mammalian predators, (2) introduced mammals induce behavioural shifts in native lizards, and (3) lizard behavioural patterns and chemosensory predator detection abilities vary according to exposure to introduced mammals. Trends in capture rates of five sympatric native lizard populations over a 23 year (1984-2006) period demonstrate that not all lizard populations that have persisted thus far on New Zealand’s mainland have stabilised in numbers. Large, nocturnal and terrestrial species remain highly vulnerable at mainland sites. Introduced kiore, Rattus exulans, induce behavioural changes in Duvaucel’s geckos, Hoplodactylus duvaucelii. A radio telemetric study demonstrated that geckos start reverting to natural use of habitats within six months of kiore eradication. Activity patterns of common geckos, H. maculatus, and common skinks, Oligosoma nigriplantare polychroma, in laboratory trials are also correlated with their exposure to mammalian predators. Lizard activity (time spent moving) increases relative to freeze behaviour with greater exposure to mammals. However, specific antipredator behaviours are not elicited by chemical cues of either native (tuatara, Sphenodon spp) or introduced (ship rat, R. rattus) predators. Lizard populations may persist by changing their behaviours in the presence of invasive mammals. However, the continued declines of particularly vulnerable mainland lizard taxa suggest that mammal-induced behavioural shifts may only slow population declines rather than enabling long-term survival. Eradicating pest mammals from offshore islands has proven effective at restoring both populations and behaviours of native lizards, but lizard populations on the mainland also deserve conservation priority. Research directed at understanding the synergistic effects of invasive species that are causing continued lizard population declines and mammal-proof fencing to protect the most vulnerable mainland populations from extinction are both urgently required.</p>