The researchers also tested neotropical migrants those birds that live in the tropics much of the year, but migrate north to temperate climates such as the United States and Canada to breed.
Results showed these birds expended more energy than those species that live year-round in the tropics, but still used less energy than birds that were permanent residents in Ohio.
"These birds have a tropical lifestyle, even though they come up north to breed, and that tropical lifestyle is consistent with a reduced metabolic rate," Williams said.
In another experiment, the researchers tested peak metabolic rate (PMR) how much energy birds expended to keep warm when exposed to cold temperatures. Results showed tropical birds had a PMR that was 34 percent lower than temperate birds. This suggests the physiology of tropical birds is indeed different from that of temperate birds and this affects their metabolism.
"Tropical birds are unable to create as much heat as temperate species through shivering. Their bodies are not built for that," Wiersma said.
To measure BMR and PMR, the researchers used a standard test in which they placed the birds in airtight steel containers with airflow in and out carefully controlled and monitored. The birds were allowed to get accustomed to the container, and then the researchers measured their oxygen consumption, which leads to the BMR and PMR values. (PMR is measured at very cold temperatures, while BMR is natural temperatures.)
Scientists have believed that tropical birds may have a slower pace of life because it fits with the rest of their life history, Williams said. Tropical birds, compared to those from temperate regions, tend to live longer, and produce fewer offspring which develop slowly and mature relatively late in life.
Among other species, this slower pace of life
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Contact: Popko Wiersma
Wiersma.6@osu.edu
614-292-3393
Ohio State University
22-May-2007