Program
Biology
College
Arts and Sciences
Student Level
Doctoral
Start Date
10-11-2022 4:30 PM
End Date
10-11-2022 5:30 PM
Abstract
Hummingbirds are the smallest of migratory birds. Their use of hovering flight to feed on nectar results in prodigious rates of energy consumption. At night, when birds are unable to feed, body fat must be used to stay warm. These characteristics make migratory flights to and from northern breeding areas very expensive. To offset these costs, hummingbirds alternate long flights with stopover periods of refueling along the way. Body fat stores, which may account for as much as 40% of a bird's body weight, also provide a buffer if birds find themselves in a nectar "desert" when the need to refuel arises. These challenges have led hummingbirds to another energetic strategy for sparing energy - the use of nocturnal torpor, which is a regulated state of decreased metabolism and body temperature. We examined the interaction between fat stores and the use of torpor as a fat sparing tool. We hypothesized that body fat levels might determine torpor use. We predicted that torpor use would be widespread to minimize refueling durations to spare fat. Alternatively, low body fat might induce torpor in case inclement weather or nectar shortages prevented foraging the next day. We measured body fat and made overnight measurements of metabolism, body temperature and torpor use in 1,328 Rufous, Calliope, Broad-tailed and Black-chinned Hummingbirds during migration. We found that hummingbirds with the least fat were more likely to enter torpor. On average, birds that stayed "hot" burned about twice as much fat as those that used torpor during their overnight fast. Torpor use thus reduces the risk of starvation but may increase the risk of predation because birds are completely helpless during torpor. Rapid climate warming and chronic drought may produce "dry" nectar corridors where birds cannot find enough energy to refuel adequately. Although fat storage and torpor may help mitigate these challenges, it is unclear how climate induced changes in nectar availability during migration might affect hummingbird fitness and which species may be most affected.
Energy Management in Migrating Hummingbirds
Hummingbirds are the smallest of migratory birds. Their use of hovering flight to feed on nectar results in prodigious rates of energy consumption. At night, when birds are unable to feed, body fat must be used to stay warm. These characteristics make migratory flights to and from northern breeding areas very expensive. To offset these costs, hummingbirds alternate long flights with stopover periods of refueling along the way. Body fat stores, which may account for as much as 40% of a bird's body weight, also provide a buffer if birds find themselves in a nectar "desert" when the need to refuel arises. These challenges have led hummingbirds to another energetic strategy for sparing energy - the use of nocturnal torpor, which is a regulated state of decreased metabolism and body temperature. We examined the interaction between fat stores and the use of torpor as a fat sparing tool. We hypothesized that body fat levels might determine torpor use. We predicted that torpor use would be widespread to minimize refueling durations to spare fat. Alternatively, low body fat might induce torpor in case inclement weather or nectar shortages prevented foraging the next day. We measured body fat and made overnight measurements of metabolism, body temperature and torpor use in 1,328 Rufous, Calliope, Broad-tailed and Black-chinned Hummingbirds during migration. We found that hummingbirds with the least fat were more likely to enter torpor. On average, birds that stayed "hot" burned about twice as much fat as those that used torpor during their overnight fast. Torpor use thus reduces the risk of starvation but may increase the risk of predation because birds are completely helpless during torpor. Rapid climate warming and chronic drought may produce "dry" nectar corridors where birds cannot find enough energy to refuel adequately. Although fat storage and torpor may help mitigate these challenges, it is unclear how climate induced changes in nectar availability during migration might affect hummingbird fitness and which species may be most affected.
