CR 74:161-170 (2017)  -  DOI: https://doi.org/10.3354/cr01496

ABSTRACT: Many tropical endotherms are already confronted by ambient temperatures (T_a) close to their body temperature (T_b) and risk severe hyperthermia due to global warming. Tropical fruit bats play a vital role in the ecosystem and their absence could have dire consequences for ecosystem health. Many fruit bats have exposed roosting habits that increase their vulnerability to heat stress. We investigated the thermoregulatory capacity of wild caught lesser dog-faced fruit bats Cynopterus brachyotis from the Island of Borneo; a heterothermic 32 g foliage-roosting generalist bat. We determined the effect of T_a (21-36°C) on metabolism, T_b and evaporative cooling. We also measured the T_a and relative humidity (RH) at capture sites. The bats displayed a seemingly narrow thermoneutral zone of 30 ± 1°C, a basal metabolic rate of 5.60 ± 0.26 W kg^-1 (1.01 ± 0.05 ml O₂ g^-1 h^-1) and a normothermic T_b of 32.5 ± 0.3°C; all much lower than expected. Evaporative cooling was only effective at T_a ≤ 31°C, above which heat storage became apparent. Bats typically entered torpor at T_a < 25°C and thermoconformed (i.e. allowed their T_b to fluctuate with T_a) at T_a > 32°C. The microclimate at capture sites remained cool (T_a = 24-25°C) and humid (RH > 90%). Our study supports the argument that tropical endotherms are susceptible to hyperthermia due to their low T_b. Further, we discuss the potential advantage of heterothermy in coping with short-term heatwaves. However, the future of these bats, and likely other low T_b species, depends primarily on their thermally buffered habitats, and decisive conservation action is required to protect thermal refugia.

KEY WORDS: Hyperthermia · Body temperature · Torpor · Global warming · Tropics · Fruit bats