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In order to determine what birds normally do, Gary Schnell and Jenna Hellack of the University of Oklahoma used Doppler radar, a device similar to that used by police to catch speeders, to measure the ground speeds of a dozen species of seabirds (gulls, terns, and a skimmer) near their colony. They also measured wind speeds with an anemometer, and used those measurements to estimate the airspeeds of the birds. (The wind speeds were generally measured closer to the ground than the birds were, which led to some errors of estimation, since friction with the surface slows air movements near the ground.)
Airspeeds were found to be mostly in the 10-to-40-mph range. The power requirements of each bird at each speed could be calculated, and that information was used to establish that the birds were generally compromising between maximizing their range and minimizing their metabolic rates with more emphasis on the former. Airspeeds varied a great deal, but near the minimum metabolic rate rather large changes in airspeed did not require dramatic rises in energy consumption. For example, a gull whose most efficient loiter airspeed was 22 mph could fly at anything between 15 and 28 mph without increasing its metabolic rate more than 15 percent.
In order to determine what birds normally do, Gary Schnell and Jenna Hellack of the University of Oklahoma used Doppler radar, a device similar to that used by police to catch speeders, to measure the ground speeds of a dozen species of seabirds (gulls, terns, and a skimmer) near their colony. They also measured wind speeds with an anemometer, and used those measurements to estimate the airspeeds of the birds. (The wind speeds were generally measured closer to the ground than the birds were, which led to some errors of estimation, since friction with the surface slows air movements near the ground.)
Airspeeds were found to be mostly in the 10-to-40-mph range. The power requirements of each bird at each speed could be calculated, and that information was used to establish that the birds were generally compromising between maximizing their range and minimizing their metabolic rates with more emphasis on the former. Airspeeds varied a great deal, but near the minimum metabolic rate rather large changes in airspeed did not require dramatic rises in energy consumption. For example, a gull whose most efficient loiter airspeed was 22 mph could fly at anything between 15 and 28 mph without increasing its metabolic rate more than 15 percent.
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