Abstract
Amphibians represent the most globally threatened vertebrate taxa on our planet, with between 30 – 50% of all species threatened with extinction. The reasons for these declines are multifaceted and vary by species however, habitat loss, modification, and degradation are recognized as some of the main contributors to the current extinction crisis. Foundational information on the spatial ecology of amphibian species can allow conservation practitioners to accurately assess the threats to a particular species and then distribute funding and effort to have the largest impact on the preservation of a species. New Zealand has three endemic species of amphibian, all anurans classified within the genus Leiopelma. Because of their cryptic nature, many gaps in information regarding Leiopelma hamiltoni spatial ecology persist despite decades of research. The primary aim of this thesis is to resolve uncertainties surrounding L. hamiltoni spatial ecology and microhabitat use through biotelemetry techniques.
The aim of Chapter 2 was to evaluate the use of biotelemetry in amphibians. Here I synthesised biotelemetry methods and outcomes from two decades of published studies (n = 128; 1 January 2000 – 31 December 2020). The most commonly used harness designs for external transmitter attachment and surgical methods for internal implantation are described, and the benefits and potential problems of these methods are discussed. I recommend improved practices for future studies and address gaps within the current amphibian telemetry literature regarding the reporting of study endpoints and study subject survival.
The aim of Chapter 3 was to develop and test an effective tracking/telemetry technique that would enable repeated observations to be made of individual leiopelmatid frogs when active and within retreat sites. I describe the application of a waist-harness style radio telemetry package for use on two of New Zealand’s native terrestrial frogs (Leiopelma archeyi and L. hamiltoni). After confirming the harness would not negatively impact captive individuals, I fitted harnesses to L. hamiltoni in Te Pākeka/Maud Island Scientific Reserve, northern South Island, New Zealand and on four L. archeyi within the Wharekirauponga area of the Coromandel Forest Park, north-eastern North Island. Although the use of radio telemetry on leiopelmatids is not without difficulties, the observations collected during field trials provide support that a waist-harness design is a suitable and effective method to conduct short-term radio telemetry on leiopelmatid frogs.
The aims of Chapter 4 were to describe the activity patterns of L. hamiltoni and determine what microclimatic and environmental factors best explain L. hamiltoni habitat use. Leiopelma hamiltoni were tracked in October of 2020 and September of 2021 using radio telemetry. The frogs were largely sedentary but did move to switch between multiple retreat sites. Leiopelma hamiltoni selected active sites with greater canopy cover than random sites and selected retreat sites with less canopy cover than random sites. Leiopelma hamiltoni retreat sites also had greater rock cover than active sites. These results provide novel information about the habitat use of L. hamiltoni and can help inform location selection for future translocations and reintroductions.
Finally, the aim of Chapter 5 was to use movement and location data collected in Chapter 4 to develop accurate utilisation distribution estimates of free-roaming L. hamiltoni on Te Pākeka/Maud Island. The utilisation distributions produced incorporated both active locations and below-ground retreat site locations of L. hamiltoni. I also examined if frog size (snout vent length) or retreat site use influenced the size of L. hamiltoni utilization distributions. The average area of L. hamiltoni 95% utilisation distributions during the austral spring was 13.6 m2 though the majority of L. hamiltoni had 95% utilisation distributions below 20 m2 and displayed high site fidelity during the study’s observation period. Leiopelma hamiltoni were largely sedentary often not moving from their retreat sites for multiple days. While my findings indicate that over a short observation period frogs generally maintain small utilisation distributions, 12.8% of the frogs tracked had estimated UDs over 26 m2 and up to 70.3 m2, indicating they are capable of using resources far outside the 13.6 m2 average utilisation distribution area reported here.
The use of the radio telemetry techniques tested and discussed within this thesis represent a major advance allowing researchers to expand observations beyond the traditional visual search data that has, thus far, been the preferred method of data collection for leiopelmatid frogs. This study is the first to monitor individual activity and habitat use across multiple days both above and below-ground. The findings of this study reinforce the existing literature concerning L. hamiltoni habitat selection, activity patterns, and home range size. However, my results offer novel findings regarding the relationship between individual movement and home range size and microclimatic variables, body condition, and individual size. This thesis has highlighted that even in a historically well studied species, emerging technology can be used to observe novel behaviours and could be refined and used in the future to answer some of the most challenging questions regarding a species ecology.