Thermoregulation by Kangaroos from Mesic and Arid Habitats: Influence of Temperature on Routes of Heat Loss in Eastern Grey Kangaroos (Macropus giganteus) and Red Kangaroos (Macropus rufus)
We examined thermoregulation in red kangaroos (Macropus rufus) from deserts and in eastern grey kangaroos (Macropus giganteus) from mesic forests/woodlands. Desert kangaroos have complex evaporative heat loss mechanisms, but the relative importance of these mechanisms is unclear. Little is known of the abilities of grey kangaroos. Our detailed study of these kangaroos' thermoregulatory responses at air temperatures (Ta) from −5° to 45°C showed that, while some differences occur, their abilities are fundamentally similar. Both species show the basic marsupial characteristics of relatively low basal metabolism and body temperature (Tb). Within the thermoneutral zone, Tb was 
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$$36.3^{\circ }\pm 0.1^{\circ }$$
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$$\overline{X}\pm \mathrm{SE}\,$$
\end{document} ) in both species, and except for a small rise at Ta 45°C, Tb was stable over a wide range of Ta. Metabolic heat production was 25% higher in red kangaroos at Ta −5°C. At the highest Ta (45°C), both species relied on evaporative heat loss (EHL) to maintain Tb; both panting and licking were used. The eastern grey kangaroo utilised panting (76% of EHL) as the principal mode of EHL, and while this was so for red kangaroos, cutaneous evaporative heat loss (CEHL) was significant (40% of EHL). CEHL appeared to be mainly licking, as evidenced from surface temperatures. Both species utilised peripheral vascular adjustments to control heat flow, as indicated by changes in dry conductance (Cdry). At lower temperatures, Cdry was minimal, but it increased significantly at Ta just below Tb (33°C); in these conditions, the Cdry of red kangaroos was significantly higher than that of eastern grey kangaroos, indicating a greater reliance on dry heat loss. Under conditions where heat flows into the body from the environment (Ta 45°C), there was peripheral vasoconstriction to reduce this inflow; Cdry decreased significantly from the values seen at 33°C in both kangaroos. The results indicated that, while both species have excellent thermoregulatory abilities, the desert red kangaroos may cope better with more extreme temperatures, given that they respond to Ta 45°C with lower respiratory evaporation than do the eastern grey kangaroos.