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The great frigatebird, a species of seabird found across the world’s tropical seas, has a 7 foot wingspan — the largest of any bird species its size. Past research had indicated that these adept pilots could stay aloft as long as a week at a time. It turns out, that the experts and even Christopher Columbus, who noticed the birds on his 1492 voyage to the Americas — and remarked “does not alight on the sea nor depart from land 20 leagues (70 miles)” — had vastly underestimated the magnificent bird’s flying prowess and smarts!
The indepth study of the frigatebirds, published in the journal Science on July 1, was led by Henri Weimerskirch of the Chizé Center for Biological Studies in France. It involved attaching solar-powered transmitters to 50 frigatebirds on Europa Island, a channel located between Mozambique and Madagascar. In addition to tracking each bird’s location, the tiny devices that weighed less than 10 grams, also collected data on the bird’s heart rate, speed, and altitude. From June to October, adult birds left the island and headed northwest to the Seychelles, a distance of about 1,548 miles. The researchers, who observed the birds from 2011 to 2015, say that instead of heading to their destination directly, many of the birds flew in large loops around the equator and the Indian Ocean.
What stunned the scientists was that the birds traveled an average of 255 miles a day and managed to stay aloft for over two months at a time. One tagged juvenile flew for 185 days and covered a mind-boggling distance of 34,000 miles, with only a four-day break in between. Weimerskirch says the four years worth of data shows that a majority of the tagged birds were motionless for about two to twelve minutes at a time, leading the team to conclude that the frigatebirds may have evolved to forgo sleep. Even those that took breaks did so for just 8 to 48 hours at a time.
The clincher? Frigatebirds traverse the mind-boggling distances without expending much energy. To get to their desired altitude without “breaking a sweat,” the birds catch a ride on the rising columns of warm air found under cumulus clouds. Once they reach a comfortable altitude, they glide along, sometimes for as long as 40-miles without flapping a wing!
When in need of an additional boost, the frigatebirds will fly inside the turbulent cumulus clouds that even airplanes avoid. But frigatebirds don’t mind the cloud’s strong air currents that propel them further upwards at the rate of 13 to 16 feet per second. The roller-coaster ride gives the birds an extra bit of altitude to glide on before catching the next air drift. As a result, frigatebirds can be found as high as 12,000 feet (4,000 meters). Weimerskirch says, “There is no other bird flying so high relative to the sea surface." What is surprising is that the tropical birds have no issues surviving the low oxygen levels and frigid temperatures found at high altitudes.
There is, of course, a good reason frigatebirds have learned to stay in the air so long. Despite being a seabird, they do not have waterproof feathers. Also, the incredible fliers can barely walk, and not swim at all. Since they are unable to grab unsuspecting prey from the water like other seabirds, frigatebirds bully birds in flight, forcing them to give up their meal (see video below). They are also experts at catching flying fish and squid that rise above the water’s surface to escape from predators like tuna and dolphins.
Since the birds are constantly airborne, researchers have little knowledge about their population size. However, there is a strong suspicion that it is on a decline. University of Washington biologist Raymond Huey and oceanographer Curtis Deutsch believe climate change could prove to be dangerous for the birds that depend on the atmospheric conditions above the oceans for both meals and transportation. According to the researchers, the shifting trade winds in the West help phytoplankton thrive, which in turn attracts more fish and squid that the frigatebirds depend on for food. Rising sea temperatures are causing the phytoplankton to decline and leading to increasingly intense tropical storms – both of which could affect nature’s “energizer bunnies.”
Resources: Latimes.com. science.com, phsy.org, washingtonpost.com