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Hummingbird foraging and the relation between bioenergetics and behaviour.
1Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106-9610, USA. suarez@lifesci.ucsb.edu
Summary
Hummingbirds use carbohydrates for short flights and fat for migration. Their metabolism and behavior coevolved to maximize energy gain, influencing nectar evolution.
Area of Science:
- Avian physiology
- Metabolic biochemistry
- Ecology
Background:
- Hummingbirds exhibit exceptionally high mass-specific aerobic metabolic rates due to their size and flight demands.
- Enzymatic capacities suggest both carbohydrate and fatty acid oxidation can fuel flight.
Purpose of the Study:
- Investigate substrate utilization during foraging versus migratory flight in hummingbirds.
- Examine the energetic trade-offs of refueling in cold environments.
- Determine factors limiting maximum sustained metabolic rates.
Main Methods:
- Analysis of enzymatic flux capacities for carbohydrate and fatty acid oxidation.
- Observation of hummingbird refueling behavior and energetics in subalpine meadows.
- Assessment of energy balance under varying sucrose concentrations and ambient temperatures.
Main Results:
- Short foraging flights are fueled by carbohydrate oxidation, while migratory flight relies on fat.
- Refueling hummingbirds in cold conditions achieve net energy gain despite high thermoregulation and flight costs.
- Low sucrose concentrations at low temperatures lead to energy deficit and mass loss.
Conclusions:
- Hummingbird behavior and metabolism appear coevolved to maximize net energy gain.
- Kidney function may limit intake rates and thus maximum sustained metabolic rates.
- Energetics of thermoregulation and flight likely influenced the evolution of floral nectar sucrose content.