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, 3 (3), 476-483
eCollection

How to Keep Cool in a Hot Desert: Torpor in Two Species of Free-Ranging Bats in Summer

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How to Keep Cool in a Hot Desert: Torpor in Two Species of Free-Ranging Bats in Summer

Artiom Bondarenco et al. Temperature (Austin).

Abstract

Small insectivorous tree-roosting bats are among the most taxonomically diverse group of mammals in Australia's desert, yet little is known about their thermal physiology, torpor patterns and roosting ecology, especially during summer. We used temperature-telemetry to quantify and compare thermal biology and roost selection by broad-nosed bats Scotorepens greyii (6.3 g; n = 11) and Scotorepens balstoni (9.9 g; n = 5) in Sturt National Park (NSW Australia) over 3 summers (2010-13). Both vespertilionids used torpor often and the total time bats spent torpid was ∼7 h per day. Bats rewarmed using entirely passive rewarming on 44.8% (S. greyii) and 29.4% (S. balstoni) of all torpor arousals. Both bat species roosted in hollow, cracked dead trees relatively close to the ground (∼3 m) in dense tree stands. Our study shows that torpor and passive rewarming are 2 common and likely crucial survival traits of S. greyii and S. balstoni.

Keywords: bats; desert; passive rewarming; scotorepens greyii and scotorepens balstoni; torpor.

Figures

Figure 1.
Figure 1.
Skin temperature fluctuations (upper trace, dotted line) of S. greyii and S. balstoni in summer with ambient temperature (lower trace, solid line) and torpor threshold (dashed line).
Figure 2.
Figure 2.
Total time bats spent torpid per day as a function of average daily Ta for S. greyii (linear mixed-effects model: t31 = 5.28, p < 0.001, R2 = 0.71; log10 Total time torpid [h] = −0.080 × average daily Ta [°C] + 2.690; n = 10, N = 42) and for S. balstoni (linear mixed-effects model: t16 = 7.46, p < 0.001, R2 = 0.91; log10 Total time torpid [h] = −0.098 × average daily Ta [°C] + 3.098; n = 5, N = 22).
Figure 3.
Figure 3.
Minimum Tskin during torpor as a function of TBD (a) and the differential between minimum Tskin during torpor and minimum daily Ta as a function of TBD (b) described by an exponential function (S. greyii: y = 1.603 + 7.620 × e(−0.570 × x), F2,59 = 22.25, R2 = 0.43, p < 0.001; S. balstoni: y = 2.237 + 4.594 × e(−0.271 × x), F2,30 = 4.33, R2 = 0.22, p = 0.022). Note the increase in Tskin variability after 1 h into torpor (a, dashed line).
Figure 4.
Figure 4.
Distribution of start times of rewarming from torpor over 24 h for S. greyii and S. balstoni. Most often, passive only arousals occurred between 06:00 and 08:00 in both species.

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