How Do Great Frigates Fly For So Long?

How Do Great Frigates Fly For So Long?

It is not unusual for birds to fly huge distances on their migratory flights around our planet, but great frigates can stay in flight for two whole months without landing or taking a rest.

Henri Weimerskirch led a team of biologists at the French National Center for Scientific Research, who just revealed the findings of their latest study on great frigates (Fregata minor). The sea birds are found in the central Indian and Pacific Oceans, and the findings are fascinating, writes William Herkewitz for Popular Mechanics.

Scientists discover new information on fascinating sea birds

Researchers attached super-lightweight GPS trackers to 48 birds in order to follow their movements. They found that they stayed in the air for up to 56 days, and could glide for hundreds of miles each days by flapping their wings only once every six minutes. The birds reached altitudes of up to two miles as they rode the updrafts.

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Before this new research, “it was known that frigate birds could stay several days aloft,” says Weimerskirch, “but that they can stay two months [continuously in the air] is completely unexpected.” The team published their findings in the journal Science.

Frigate birds were previously known to have the lowest wing load of any species. This means that they have the smallest body weight when distributed over the area of their wings. Although great frigates are seabirds, they do not have water-repellent feathers. As a result they cannot land and float on water.

Updrafts propel great frigates above Indian Ocean

Great frigates are able to stay airborne using unique weather patterns found in the center of the Indian Ocean. By tacking into updrafts they are carried high into the air, and do not have to flap their wings as much.

Large parts of the Indian Ocean are windless for much of the year, but the areas immediate alongside them have reliable weather conditions that the great frigates can use to stay in the air. It is thought that the birds are somehow sleeping in the air as they stay up in the clouds for up to two months at a time.

Weimerskirch and his team discovered that at some points the birds’ heart rate was the same in the air as when they are sitting in the nest. They concluded that at these points flying was almost effortless.

Study improves knowledge of sea birds

Prior to the study scientists thought that great frigates used clouds to find updrafts. However they believed that the birds were unlikely to enter the cloud due to the potential for turbulence. This theory has now been disproved.

“Our study shows that they do it intentionally,” says Weimerskirch. The idea is to use the turbulence inside clouds to gain more altitude in order to glide to the next far away cloud.

Although some birds were seen flying at 2.5 miles above the ground, where there is little oxygen and water becomes ice, most fly between 150 to 2,000 feet above the sea. The study has helped to greatly improve our understanding of an impressive sea bird, but it would be interesting to find out whether great frigates are getting any sleep as they glide around for up to two months.

If they are found to not be sleeping at all, it would be a remarkable development. However it would be amazing if they were somehow controlling their movements while also getting some much needed rest.

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