20.3 Wednesday, Jan. 4 Torpor-assisted migration in bats MCGUIRE, LP*; JONASSON, KA; GUGLIELMO, CG; Univ. Western Ontario, London email@example.com
Optimal migration theory predicts that migrating animals should seek to minimize some combination of energy, time, or mortality risk. These factors trade-off with each other; animals may spend longer refuelling, increasing energy intake at the expense of time or vice versa. For migratory birds, the trade-off between energy and time lies largely in energy expenditure during periods of stopover. Birds spend twice as much energy during stopover as in migratory flight, largely due to thermoregulatory costs. In a recent study, we found that migrating silver-haired bats (Lasionycteris noctivagans) made only 1-2 day stopovers at a site where similar sized birds stayed for one week or longer. We suggested that bats’ ability to use daily torpor to minimize energy expenditure may allow the bats to forego extended refuelling stopovers and rather minimize time instead. Here I will present results of a follow-up study combining temperature sensitive radio-telemetry and respirometry at a range of local daytime temperatures. Free-living silver-haired bats regularly used torpor in response to declining ambient temperature. As daytime temperatures approached 27 – 30 ° C or warmer, bats remained normothermic. Below this threshold temperature all bats used torpor, regardless of age or sex. In many cases the bats entered a deep torpor for the entire day, re-warming to depart at sunset. Combining the daily temperature profiles of free-living bats and metabolic measurements from respirometry demonstrates that migrating bats incur very low daily energy costs. Thus bats are able to use a torpor-assisted migration strategy to minimize energetic costs during non-flight periods. Consequently the need for refuelling stopover is virtually eliminated and migrating bats are able to minimize time independent of energy minimization trade-offs.