Frigate birds are truly incredible creatures. With their 6-foot wingspan, these animals can stay aloft for weeks without having to touch down the ground and rest.
But exactly how frigate birds can manage this remarkable feat has long been a mystery for scientists. In a new telemetric study, an international team of scientists sought out to find the answer.
How Frigate Birds Stay Up In The Air For Months
Frigate birds are aquatic birds whose feathers are not waterproof, so they cannot rest on the waves. When male frigate birds try to attract females, the vivid red pouch on their throat gets inflated. They're also known for stealing other sea birds' food.
These animals spend most of their life at sea, but their habits on land are not well-known. Because of that, scientists began tracking them down in the Indian Ocean.
Henri Weimerskirch, an ornithologist from the National Center for Scientific Research, placed satellite tags and several instruments on a dozen of frigate birds. The instruments were capable of measuring heart rate and other body functions.
Then the data flew in. Weimerskirch and his colleagues first found that the birds can reach at least 1,500 meters and then it went higher and higher — 2,000 meters; 3,000 meters; and 4,000 meters. At this altitude, the conditions are already frigid.
Four thousand meters is roughly equivalent to 12,000 feet. For comparison, it is as high as the Rocky Mountains. Weimerskirch says no other bird has flown so high relative to the surface of the sea.
Frigate birds' exemplary flight abilities should take up much energy, he says. But the instruments that monitored the heart rate of the animals revealed that they appeared not to be struggling at all. How did that happen?
As it turns out, frigate birds take advantage of two things so they could spend less energy while flying thousands of meters every day.
First, frigate birds intentionally enter into a cloud — a fluffy, white cumulus cloud. Scientists say the animals hitch a ride on the updrafts or small-scale rising air to get to the top of the cloud. It works because their unusual body has a higher ratio of wing surface compared with body weight. This is known as "wing loading."
Second, the birds capitalize on the winds that form the updrafts, which can disrupt the waves at the sea surface. When the waves are disrupted, deeper water can rise to the surface, bringing with it phytoplankton that lure small fish, which in turn attracts the bigger fish — the frigate bird's next meal.
"It's a very, very specific niche and way of attacking prey," adds Weimerskirch.
Details of the study are published in the journal Science.
Photo: Ben Ketaro | Flickr