The use of torpor in reproductive female Hemprich's long-eared bats (Otonycteris hemprichii)

We investigated the patterns of torpor use and body temperature (T _b) in reproductive Hemprich's long-eared bats (Otonycteris hemprichii; body mass ̃20 g) in the central Negev Desert highlands. We hypothesized that T_b regulation in female O. hemprichii during reproduction is shaped by a trade-off between the energy and temperature requirements of embryo and pup growth and the mother's own need to use torpor and passive rewarming to save energy and water. We predicted that patterns of torpor use change during pregnancy but change little if at all during nursing. We used radio telemetry to track, find the roosts of, and measure the skin temperatures of eight pregnant and 15 nursing bats during the years 2002-2004; we measured roost temperature (T_r) using temperature data loggers. Before field data collection, we simultaneously measured skin temperature and T_b in three female bats in the laboratory and derived field body temperatures (T_bf) from these data. Female bats often used both deep and shallow daily torpor during the first two trimesters of pregnancy, with T_bf frequently dropping as low as 15°C. Pregnant females used only shallow torpor during the last trimester of pregnancy, perhaps to permit faster growth of the embryo. During nursing, the bats used only shallow torpor, with T_bf always >29°C, possibly to facilitate milk production. T_bf of pregnant and nursing bats varied with daily oscillations in T_r. Passive rewarming was not evident before the animals exited their roosts to forage.