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Microclimatic aspects of retreat site and basking site selection by the Tasmanian tiger snake, Notechis ater sp. (Serpentes: Elapidae)


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Whitaker, PB 1992 , 'Microclimatic aspects of retreat site and basking site selection by the Tasmanian tiger snake, Notechis ater sp. (Serpentes: Elapidae)', Honours thesis, University of Tasmania.

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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.

Item Type: Thesis - Honours
Authors/Creators:Whitaker, PB
Copyright Holders: The Author
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Copyright 1992 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
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