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Frigatebirds. Photo: Ronald Toppe

Meet the aerial acrobats

3 months ago
Written by Hanna Thevik, Ronald Toppe
Ocean education > Meet the aerial acrobats

Meet the aerial acrobats

3 months agoOcean education
Written by Hanna Thevik, Ronald Toppe
Frigatebirds. Photo: Ronald Toppe

As Statsraad Lehmkuhl approached the coast of Brazil, beautiful black birds appeared: Frigatebirds. They sailed above the ship, almost like paper airplanes.

The frigatebirds might look scary. Black, with pointed wings, and a long thin cleaved tail. They are large, the wingspan can reach two meters. The beak is long and narrow, with a hook at the end.

But for sailors, the birds are a good omen. Frigatebirds around the masts mean that land is not far away.

- There are five different species, says Lars Udsen. He is a volunteer crew on board, and really fascinated by the birds.

- They are cool animals that can fly for weeks on end.

Lars Udsen. Photo: Hanna Thevik
Lars Udsen. Photo: Hanna Thevik

Acrobats

The long beak reveals how the frigatebirds get their food. They pick it up elegantly from the sea, as with tweezers. The birds are pure acrobats in the air, and specialize in chasing other birds until they gulp up their prey, and then swoope over the waves and retrieve.

But normally they just hover high up in the sky, scouting for a shoal of small fish that are frightened to the surface by tuna or whales.

The beak is as a pair of tweezers. Photo: Ronald Toppe
The beak is as a pair of tweezers. Photo: Ronald Toppe

The frigatebirds prefer not to land on the sea.

- They have such short and small feet in relation to the long wings, that they both have difficulty walking on land and taking off from the sea. They thrive best in the air, to put it that way, Lars smiles.

Use the elevators

Scientists attached sensors to the birds to find out how they could stay out at sea for so long without wearing themselves out completely.

They discovered that the birds were hiking with the clouds.

They find a cumulonimbus cloud, the kind that gives us heavy showers. Inside them, the air rises straight up, and lifts the birds upwards at a speed of four to five meters per second. At the right height, the frigatebird glides out of the cloud, and floats many kilometers away, without a single wingbeat.

- Some of them were 4000 meters above sea level! Tough creatures, says Lars enthusiastically.

Frigatebirds have the largest wing-area-to-body-weight ratio of any bird. Photo: Ronald Toppe
Frigatebirds have the largest wing-area-to-body-weight ratio of any bird. Photo: Ronald Toppe

Are they sleeping?

One of the birds the researchers followed was contiguous in the air for two months.

Lars wonders if they sleep with only half the brain at a time, but the researchers simply do not know. They have seen that the birds at times sail without moving their wings at all, at the same time as the heart rate is as low as when they are lying on the nest. It is possible that they then simply doze off a little while in the air.

Showing off to the ladies. Photo: Ronald Toppe
Showing off to the ladies. Photo: Ronald Toppe

Red balloon

The males have a bare spot on the neck. During the mating season, it is inflated to a huge balloon, to tempt the ladies. The nests are not as impressive, some dry grass and twigs, which are often stolen from the neighbor.

The frigatebirds lay only one egg, and take care of the young for so long that they only mate every other year.

Female frigatebird with a chicken in her nest. Photo: Ronald Toppe
Female frigatebird with a chicken in her nest. Photo: Ronald Toppe

- You could always count on them returning to the island where they have their a nest, so it is said that the Polynesians sent letters to each other with the frigate birds, says Lars.

Two of the five species of frigatebirds are at risk of extinction, due to overfishing and destruction of breeding grounds.

Source: forskning.no

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