What is a frigatebird?

A frigatebird is a large, black tropical seabird with long, narrow, angled wings and a deeply forked tail. Frigatebirds have the biggest wing area relative to body weight of any bird, which lets them soar for days without flapping.

There are five species in a single genus, Fregata: the magnificent, great, lesser, Ascension and Christmas Island frigatebirds. The great frigatebird has a wingspan of 205–230 cm but weighs only about 1.0–1.6 kg. Females are larger than males and, in most species, have white on the breast; adult males are all black with a throat sac that turns scarlet in the breeding season.

The name comes from sailors, who compared the birds to fast frigate warships, often used by pirates and privateers. In the Caribbean they’re also called man-o’-war birds. Frigatebirds belong to the order Suliformes with gannets and boobies and cormorants.

Why can’t frigatebirds land on water?

Their feathers aren’t waterproof enough. Frigatebirds have little preen oil, so if they settle on the sea their plumage soaks up water and they struggle to take off again.

Their legs are tiny and their feet only partly webbed, so they can’t swim or walk well either. Instead they feed on the wing, snatching flying fish, squid and baby turtles from the surface, or stealing. They rest by perching on trees, bushes or cliffs.

Do frigatebirds sleep while flying?

Yes. A 2016 study that recorded the brain activity of great frigatebirds over the ocean found they slept in flight, about 42 minutes a day, in short bouts lasting up to several minutes, mostly while soaring in rising air.

On land the same birds slept more than 12 hours a day. In flight they often rested one half of the brain at a time, keeping one eye open in the direction they were flying. The birds made non-stop foraging trips of up to about ten days, covering up to 3,000 km. Frigatebirds ride thermals under cumulus clouds up to considerable heights, then glide long distances, which is how they stay aloft so cheaply.

How do frigatebirds steal food?

By chasing other seabirds, grabbing their tails or wings and shaking them until they drop or vomit their catch, then catching it in mid-air.

Boobies and tropicbirds returning to colonies are frequent victims. Piracy is famous but not their main way of feeding. In one study of great frigatebirds harassing masked boobies, theft supplied on average about 5% of their food and at most around 40%. Most of the time frigatebirds catch their own prey near the surface, often where tuna and dolphins drive fish upward.

How do frigatebirds breed?

Slowly. Males gather in groups, inflate their red throat pouches like balloons and wave their wings to attract females flying overhead. Each pair raises one chick, and a full cycle can take two years.

Nests are flimsy platforms of sticks in trees or bushes. After the chick fledges, its parents keep feeding it for months. Great frigatebird chicks receive care for 150–428 days after fledging, the longest post-fledging care of any bird. Females first breed at 8–9 years old and males at 10–11, so populations grow very slowly.

Are frigatebirds endangered?

Three species are widespread and secure, but two island species are threatened. The Ascension frigatebird is Vulnerable, and the Christmas Island frigatebird, with an estimated 3,600–7,200 birds, is declining.

The Ascension frigatebird was confined to tiny Boatswain Bird Island for more than a century after cats arrived on Ascension. After feral cats were eradicated from the main island in 2002–2004, two pairs returned to nest there in 2012. The Christmas Island frigatebird nests only in tall forest on Christmas Island, about 10% of it outside the national park. Habitat loss, fishing and introduced species are the main threats.

How to tell the five frigatebird species apart

Location does most of the work, because the species’ ranges overlap less than you might expect. Plumage patterns on the underside help with the rest.

Young frigatebirds are trickier. Juveniles of most species have white or rusty-tinged heads and take several years to reach adult plumage, so a mixed flock over a colony can show a confusing range of patterns.

Built for the air: frigatebird flight adaptations

Everything about a frigatebird is tuned for staying aloft at the lowest possible cost. The bones are hollow and very light, and in the magnificent frigatebird the skeleton has been reported to weigh less than the feathers. The long, sharply angled wings give a huge lifting surface for a small body, and the deeply forked tail opens and closes like scissors to steer and brake during tight turns and aerial chases.

Tracking studies of great frigatebirds in the Indian Ocean have shown them climbing inside cumulus clouds to heights of several kilometres, then gliding for long distances before catching the next updraft. By linking thermals together this way, a frigatebird can cover hundreds of kilometres a day with very little flapping, which is what makes multi-day flights and sleeping on the wing possible.

What do frigatebirds eat?

Flying fish and squid are the staples, snatched from the surface or even from the air as fish leap away from tuna and other predators. Frigatebirds also pick up offal and scraps around fishing boats, and at some beaches they take newly hatched sea turtles running for the water, as well as the eggs and chicks of other seabirds.

The hooked bill is long and slender, and a frigatebird can scoop prey from the surface with a quick dip of the head while barely wetting its plumage. Because they cannot dive or rest on the sea, they depend heavily on ocean predators such as tuna and dolphins to push prey within reach, which ties them closely to the health of open-ocean fish stocks.

Frigatebirds and people

Sailors used frigatebirds as a sign that land was within a few days’ flight, and some believed their behaviour could foretell bad weather. Across the Pacific the birds have deeper cultural roots. A frigatebird flies across the flag of Kiribati, and on Nauru frigatebirds were traditionally caught and tamed, a practice tied to local status and sport. In Polynesian and Micronesian navigation traditions, seabirds in general helped wayfinders locate islands beyond the horizon.

Where can you see frigatebirds?

• Galápagos: North Seymour has easily viewed nesting colonies of great and magnificent frigatebirds, with males displaying their red pouches.
• Barbuda: the Codrington Lagoon colony is one of the largest magnificent frigatebird colonies in the Caribbean.
• Florida: magnificent frigatebirds are often seen soaring over the Florida Keys, and the Dry Tortugas holds a breeding colony.
• Christmas Island: the only place to see the Christmas Island frigatebird, often alongside great and lesser frigatebirds.

Hurricanes and strong storms sometimes carry magnificent frigatebirds far outside their usual range, so a sighting well north of the tropics after a big storm is not unheard of.