Microclimatic aspects of retreat site and basking site selection by the Tasmanian tiger snake, Notechis ater sp. (Serpentes: Elapidae)
Creators: name: Whitaker, PB
Publisher: name: University Of Tasmania
Year: 2023

description: The thermal ecologies of two elevationally isolated populations of adult female Tasmanian Tiger Snakes (Notechis ater sp.) were investigated using stomach implanted radiotelemetry and a comprehensive microclimate monitoring programme. The study sites were Egg Islands, in the Huon Valley in southeastern Tasmania, and at Lake Crescent, on the lower Western Central Plateau of Tasmania. The study had four primary ~ims: (i) to determine the microclimatic conditions associated with retreat site and basking site selection; (ii) to record and compare behavioural thermoregulatory response to micrometeorological variation; (iii) to monitor diel rhythmicity and range of body temperatures; (iv) to determine voluntary thermal limits and eccritic body temperatures. This information was used in two ways: firstly, to identify the preferred physical microhabitat of this species; and secondly, to develop two predictive models of adult female Tiger Snake activity. The first is a relatively simple empirical model based on microclimatic correlates of body temperature; the second, a biophysical approach involving analysis of the snake's energy budget. Development of the first model required identification of those environmental parameters and quantities which: (i) trigger emergence; (ii) determine the amount of time necessary for the daily warm-up phase in differing micrometeorological conditions; (iii) allow the animal to move about within its home-range; and (iv) trigger entry into retreat sites. In order to develop the second model detailed information on body temperatures and on the pertinent microclimatic variables within the animal's immediate vicinity were required. It also required information on the physical dimensions and behavioural characteristics of the animal. In addition, other questions relating to the thermal ecology of this species are asked. The determined correlates of body temperature and daily patterns of activity included total down-welling radiation, global radiation, ground surface temperature, ground heat-flux, and inground temperature. Cloud cover and wind direction were found to influence the snakes thermoregulatory behaviour. The telemetry results, determined in a temperature gradient chamber, showed elevational differences in eccritic mean body temperatures and voluntary thermal limits of non-gravid females, but similar temperatures for gravid females. The field telemetry showed diel rhythmicity and the range of body temperatures for four Egg Island females which showed differences between gravid and non-gravid females. The empirical model was found to explain daily activity and validate assumptions made necessary to develop the biophysical model. The biophysical model is a modified integrated parameter model, based on empirical relationships, and was tested against the field telemetry derived body temperature data. The model was found to explain a minimum of 65% and a maximum of 84% of the variance desplaying a high level of significance. The results show that the snakes are optimising their thermal uptake.