Effect of diet quality and ambient temperature on the use of torpor by two species of neotropical nectar-feeding bats.

Neotropical bats use torpor as a strategy to save energy when they experience a low energy intake and/or low ambient temperature ( T a ). Digestive physiology limits the energy intake of several glossophaginid bats, and could play an important role in the onset of torpor in these tropical animals. We measured the effect that diet quality and T a had on the use of torpor by the nectar-feeding bats Glossophaga soricina and Leptonycteris yerbabuenae Captive bats were fed with 5% (low) or 35% (high) sucrose solutions while exposed to two different T a (17.7 and 23.2°C; low T a and high T a ) in four different treatments: (1) high sucrose:high T a , (2) high sucrose:low T a , (3) low sucrose:high T a and (4) low sucrose:low T a We measured their energy intake, changes in body mass (Δ M b ) and skin temperature ( T skin ) as response variables. Energy intake (in 10 h) was limited when both species fed on 5% sucrose, but body mass gain was only affected in G. soricina. Energy intake and T a had a negative effect on the minimum T skin of both species, and Δ M b affected the time that G. soricina used torpor. Both species remained normothermic on the high sucrose:high T a treatment, but used torpor on the other three treatments. Bats used torpor during their resting and activity periods. Leptonycteris yerbabuenae spent more time in torpor in the low sucrose : high T a treatment, while G. soricina used this strategy for longer periods of time in the high sucrose : low T a treatment. We found that diet quality and T a played an important role in the use of torpor by nectar-feeding bats.