Recent work in Australia and Africa has shown that heterothermy is widespread among phylogenetically diverse tropical and subtropical mammalian taxa. However, data on the use of heterothermy by Neotropical mammals are relatively scant, and those studies that exist focus on insect-eating bats. We investigated the capacity of fruit-eating Neotropical bats to use heterothermy when exposed to acute cold temperatures, and compared this to previous data focused on insect-eating bats sampled from the same region and time of year. We measured rectal temperatures prior to acute cold exposure (1 hour at an air temperature of 6, 7, or 10°C), and again after exposure. Our data show considerable variation in the thermoregulatory patterns of Neotropical bats and generally, our results show that smaller bats cool quicker and to a greater extent than larger bats. Our results highlight the importance of energy conservation even in environments in which resources are relatively abundant.

Bats were captured in mist nets or harp traps set across known flight paths. Each bat was identified to species, and we recorded the individual’s age, sex and reproductive condition, and measured body mass and forearm length. Each bat was placed into a small, one-time-use cloth drawstring bag for up to 8 hours. Using cloth bags for bat containment is a common practice because they greatly reduce the risk of injury, isolate the bat from disturbances, and allow bats to hang in a natural position. All bat bags were hung in a sheltered space at our field site where bats were allowed to rest for up to 8 hours in T_a (26 – 32 ºC). This acclamatory period ensured bats would be post-absorptive and in the diurnal rest phase of their circadian cycle prior to experimental trials. After the 8 hour acclimation, we manipulated the bat bag so that only the genital area was exposed and used a sterilized, lubricated thermocouple probe to measure resting rectal T_b as a proxy of core T_b (Britzke, Sewell, Hohmann, Smith, & Darling, 2010).  Special care was taken to do this quickly so as not to prolong bats’ exposure to stimulus. Similar to Czenze & Dunbar (2017), immediately after, we closed the bag and placed it into an environmental chamber maintained at either 6, 7, or 10 ± 0.2 °C, which are within the range of historic low T_as of the area (Belize National Meteorological Service; available from http://www.hydromet.gov.bz/). After being exposed to a temperature treatment for 1 hour, we removed bats and measured rectal T_b again using the same manner as outlined above. In the wild, a normothermic bat exposed to 5 °C for 1 hour may reduce its T_b by ~30 °C (Czenze, Jonasson, & Willis, 2017); this exposure time also allowed us to operate within the confines of our permits and animal care protocols. We sampled individuals once at one of our three temperature treatments and repeated with new captures until each species had multiple representative individuals across all temperature treatments.  Upon conclusion of experimental trails, bats were allowed to rewarm in T_a and we used a disposable pipette to give bats water or diluted fruit juice to drink before releasing them at their site of capture.