Lizards at elevation: thermal ecology and emergence activity of alpine lizards in Otago

Abstract

The alpine zone is a rugged habitat that is difficult for any species to inhabit year-round. Many that do so are large mammals with specific behavioural or physiological adaptations that enhance survival in these high-elevation and often very cold environments. Lizards also inhabit this zone, but their ectothermic nature makes them especially vulnerable to the extreme temperatures and long winters. New Zealand has a number of poorly known alpine lizards in Otago, including the orange-spotted gecko (Mokopirirakau ‘Roy’s Peak’) and multiple species of Oligosoma skinks. The orange-spotted gecko is a newly discovered species that is only known from the alpine zone whereas Oligosoma skinks can be found at lower elevations. Little is known about how these lizards survive in their alpine habitat. As a result, they provide a valuable opportunity to increase our understanding of the thermal ecology of lizards living in cold environments. Information gained through studying these species can increase our ability to manage alpine lizards and improve our understanding of threats to animals living in this zone. Therefore, the aims of this thesis were to investigate the thermal ecology of these lizards, especially the orange-spotted gecko, in order to understand what temperatures, they are exposed to and how these ectotherms interact with their environment in the alpine zone. I first examined available temperatures in the alpine zone. Data loggers were placed in likely lizard microhabitats over the active season of October 2018-March 2019. These loggers recorded a wide range of temperatures including temperatures below 0°C and in excess of 50°C. I also compared daytime skin temperatures of orange-spotted with temperatures of the underside of their occupied rock to understand how lizards were thermoregulating and how this behaviour differed with reproductive status and across the active season. Reproductive females maintained higher skin temperatures than adjacent rock temperatures when the rocks were below 20° C but maintained lower body temperatures than those of their occupied rock when the rocks surpassed 25°C. When compared to other adult geckos (males and non- reproductive females), reproductive females maintained higher daytime skin temperatures, suggesting that they use the available microhabitats differently. Skin temperatures of non- reproductive females and males had a more linear relationship with rock temperatures. I also monitored the emergence behaviour of lizards to increase our understanding of activity periods and how emergence is influenced by environmental conditions. To monitor emergence, trail cameras were left in the field. Sightings of geckos and skinks were compared with temperatures gathered by the microhabitat dataloggers and with other weather variables (presence of rain, snow, and the strength of wind). I obtained evidence of the orange-spotted gecko (potentially pregnant females) openly basking during the day, which is otherwise undocumented for this nocturnally foraging gecko. I further found that strong winds negatively influenced the presence of geckos on camera at night. During the day, warm surface temperatures increase gecko presence, while presence of rain and strong winds greatly decreased sightings. Skinks were only seen by day, and presence was directly related to surface temperatures whereby more skinks were found on warm days and observations of skinks dropped dramatically when poor weather (wind and rain) were present. Lastly, I confirmed the presence of several introduced mammal species (including cats and stoats, which are known predators of lizards) in this alpine habitat. My study has provided an indication of what combination of time of day, temperature, and other weather variables create the optimal environment for orange-spotted gecko activity. We can use this information to inform monitoring programs so that the latter are conducted during optimal weather windows to increase the chances of observing lizards. With a strong monitoring programme, we can learn about threats these species face whether they be anthropogenic or from predators. Finally, knowledge gained through well informed monitoring programmes will promote effective management of alpine lizards in the future.