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The endless flight of the frigatebird

I have spent many hours at places like the rim of Lower Table Rock watching the vultures and red-tailed hawks soaring below me, and where swallows and swifts dance in the air just beyond reach. Flight is magic to me. I am also impressed by less capable fliers like the grouse that explodes from under foot, thrashing the air as it beats a panicked retreat with little grace. They can fly, and I can’t.

You might think we know all there is to know about the flight of birds, but studies keep discovering aerial feats we never imagined. Electronic devices keep getting smaller, lighter and more capable, and our ability to peer into the lives of birds increases daily.

Recently a researcher attached tiny devices to frigatebirds and followed their movements in great detail.

Frigatebirds are large black birds of tropical seas. They have incredibly long, narrow wings and a long, forked tail. Their flight is buoyant and graceful. This is due, in part, to their light frame. They are the only birds whose feathers weigh more than their skeleton. Males have a great red throat pouch they inflate to attract mates.

If you have been to a place like Hawaii, Puerto Vallarta or the Caribbean, you have undoubtedly seen them soaring “endlessly” high over the ocean on motionless wings. They also soar over the tall hotels that line the beaches where the sea breezes are deflected upward.

These pirates steal fish from other seabirds that work hard for their catch. When not thieving, they pluck food from the surface of the ocean. Oddly, for a marine bird, they cannot swim. For one to land on the water is to drown. Their feathers do not effectively repel water.

The study revealed that “endlessly” meant more than we thought. When night came, they didn’t seek out some protected roost. They flew on through the night and into the next day ... and through the next night and into the next day and on and on. Some flew continuously for two months or more. They never took a break, not once.

Even more amazing, the researchers learned frigatebirds would often fly directly into the light, fluffy cumulus clouds that create the background in most pictures taken on tropical vacations. However, if you have ever flown through one of these clouds, I’m sure you have felt the bumpy ride. The air currents are turbulent as the warm moist air inside these clouds rises high into the atmosphere. Most birds and planes avoid these clouds when possible. Not so frigatebirds.

They enter these clouds and take the rough ride to the top. With the gain in elevation of many thousands of feet, they can glide effortlessly for hours and over great distances without needing to flap. Over land, thermals provide a similar service to vultures, hawks and eagles, though with less turbulence. At night, however, thermals weaken and fail, bringing the raptors to earth.

I have a newfound respect for frigatebirds and will pay more attention to these aerial pirates on my next trip south.

Stewart Janes is a biology professor at Southern Oregon University. He can be reached at janes@sou.edu.

Lloyd Knapp submitted this photo of a frigatebird shot on Midway Atoll in 2008.