Evaluation of remote cameras for monitoring multiple invasive mammals in New Zealand
© New Zealand Ecological Society. Numerous conservation projects in New Zealand aim to reduce populations of invasive mammalian predators to facilitate the recovery of native species. However, results of control efforts are often uncertain due to insufficient monitoring. Remote cameras have the potential to monitor multiple species of invasive mammals. To determine the efficiency of cameras as a multi-species monitoring tool, we compared the detection rates of remote cameras and tracking tunnels over 4 non-consecutive days across 40 sites in Wellington. On average, cameras detected significantly more hedgehogs (Erinaceus europaeus) and rats (Rattus spp.) than tracking tunnels, and their images could be used to identify rats to the species level in 50% of detections. Cameras also detected more possums (Trichosurus vulpecula) but missed recording mice (Mus musculus) on some occasions where tracking tunnels detected them, and vice-versa. We conclude that remote cameras are well-suited for simultaneously monitoring multiple species of invasive mammals in New Zealand.
© New Zealand Ecological Society. Numerous conservation projects in New Zealand aim to reduce populations of invasive mammalian predators to facilitate the recovery of native species. However, results of control efforts are often uncertain due to insufficient monitoring. Remote cameras have the potential to monitor multiple species of invasive mammals. To determine the efficiency of cameras as a multi-species monitoring tool, we compared the detection rates of remote cameras and tracking tunnels over 4 non-consecutive days across 40 sites in Wellington. On average, cameras detected significantly more hedgehogs (Erinaceus europaeus) and rats (Rattus spp.) than tracking tunnels, and their images could be used to identify rats to the species level in 50% of detections. Cameras also detected more possums (Trichosurus vulpecula) but missed recording mice (Mus musculus) on some occasions where tracking tunnels detected them, and vice-versa. We conclude that remote cameras are well-suited for simultaneously monitoring multiple species of invasive mammals in New Zealand.
<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>
<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>
<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>
<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>
<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>
<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>
Context Invasive mammals have been removed from at least 100 offshore islands around New Zealand, covering a total area of around 45 000 ha. Aims To review the outcomes of eradications, the statutory and social environment in which the eradications were conducted, and the lessons provided for future work. Methods Native species to benefit from the eradications were identified, as were the reasons for the eradications and the agencies responsible. Examples are provided using case studies. Key results Three loosely linked work streams were revealed: research into efficient baits and baiting methods, threatened species-led projects nested within priorities for species recovery and supported by legislation, and community-led projects instigated by restoration societies. At least 180 populations of 14 species of invasive mammals were removed. Numerous species of native plants, invertebrates and more than 70 species of terrestrial vertebrates are recovering or are likely to recover as a result of the eradications. Partnerships have been formed with Māori and innovative projects developed with community groups. Conclusions Eradications of invasive mammals are aggressive conservation actions that can have wide benefits for biodiversity but can also be controversial, technically demanding and expensive. Implications Eradications are multi-scale problems. If they are to gain public acceptance, evidence is needed in support. This evidence can include understanding the detrimental effects of invasive species, the likely responses of native biodiversity, and the benefits ensuing from their recovery. However, the way this evidence is gained and communicated will also require deep understanding of nuances in regional political and cultural environments.
