Temporal patterns of foraging by silver-haired bats during migratory stopover revealed by isotopic analyses (δC) of breath CO.

The extent to which migratory bats forage at stopover sites or while in migratory flight is poorly understood. Endogenous fat stores have lower δC values relative to the dietary substrates from which they were synthesized, and so, the fed versus fasted state of bats should be discernable by comparing their breath δC at capture to that after a known period of fasting. We captured silver-haired bats (Lasionycteris noctivagans) at a stopover site at Long Point, Ontario, Canada, during spring and fall migration.

Testing the "Fasting While Foraging" Hypothesis: Effects of Recent Feeding on Plasma Metabolite Concentrations in Little Brown Bats ().

Plasma metabolite concentrations can be used to understand nutritional status and foraging behavior across ecological contexts including prehibernation fattening, migration refueling, and variation in foraging habitat quality. Generally, high plasma concentrations of the ketone β-hydroxybutyrate, a product of fat catabolism, indicate fasting, while triglycerides indicate recent feeding and fat accumulation. In recent studies of insectivorous bats, triglyceride concentration increased after feeding as expected, but β-hydroxybutyrate also unexpectedly increased rather than decreased.

Energetics of migratory bats during stopover: a test of the torpor-assisted migration hypothesis.

The torpor-assisted migration hypothesis posits that migration is facilitated in bats by the use of torpor during stopover roosting periods, and predicts that at stopover, bats regulate time in torpor facultatively so that daily energy expenditure is independent of ambient roosting temperature. Energy savings can thus be directed to migratory movement. However, direct measurements of total roosting energy expenditure in relation to ambient and body temperature are lacking.

Metabolic rate, latitude and thermal stability of roosts, but not phylogeny, affect rewarming rates of bats.

Torpor is an adaptation that allows many endotherms to save energy by abandoning the energetic cost of maintaining elevated body temperatures. Although torpor reduces energy consumption, the metabolic heat production required to arouse from torpor is energetically expensive and can impact the overall cost of torpor. The rate at which rewarming occurs can impact the cost of arousal, therefore, factors influencing rewarming rates of heterothermic endotherms could have influenced the evolution of rewarming rates and overall energetic costs of arousal from torpor.