Frigatebirds

The frigatebirds form a single genus (Fregata) and family (Fregatidae) within the order of Pelecaniformes. There are five species: magnificent frigatebird (Fregata magnificens), Ascension frigatebird (Fregata aquila), Christmas Island frigatebird (Fregata andrewsi), great frigatebird (Fregata minor) (see photo), and lesser frigatebird (Fregata ariel). An alternative name for the frigatebird is the “man o’ war bird”, which comes from its piratical behaviour.

Frigatebirds are pelagic, only coming to land to breed or roost occasionally, and they are found in the tropical regions of the Pacific and Indian Oceans, and the Atlantic Ocean to a lesser extent, with the Ascension frigatebird being confined to the seas around Ascension Island. Despite spending so much of their time over the sea, frigatebirds of all species usually stay within sight of land.

Frigatebirds are renowned as being among the pirates of the bird world, with a propensity for stealing food from other birds, in the same manner as skuas in more northerly latitudes. However, stolen food probably accounts for no more than 10% of a frigatebird’s diet, the rest being taken from the surface of the sea.


Appearance

Most frigatebird species are around 40 inches in length, although the lesser frigatebird measures only 30 inches. They are lightly built birds but have long slender wings that can be seven feet from tip to tip. The plumage colouring shows only minor variations between the species, being generally black with an iridescent purple sheen. Males have an orange throat sac that turns red when it is inflated during the mating display, whereas females have white throats. They have long forked tails and heavy beaks with a hook at the end. Females are slightly larger than males and their plumage is lighter in colour.


Behaviour

Frigatebirds are only comfortable when in flight, being very poor swimmers and very ungainly on land. Should they land in the sea, their feathers become waterlogged very quickly and taking off is extremely difficult. Likewise, they can only shuffle about on land and need to climb to a high point before they can get airborne.

However, once in the air they need to expend hardly any energy as their huge wingspan is perfectly capable of keeping their light bodies aloft for many hours at a time without a single wingbeat. The frigatebird has the greatest ratio of wing surface area to weight of any bird.

As pirates, frigatebirds will harrass pelicans, gulls, boobies and cormorants, chasing after them until they drop or regurgitate their catch. The agile frigatebird will then swoop down and take the food before it hits the water.

However, frigatebirds are excellent fishermen in their own right. A bonus is presented when flying fish are being chased by dolphins or other marine predators. The fish leave the sea to escape being eaten from below but their luck can run out if there is a frigatebird ready to take them from above.

Frigatebirds will take virtually any food that floats on the surface or comes very close to it. This can include jellyfish, squid and young turtles. Food is taken skillfully with the frigatebird’s hooked beak without their feathers getting wet.

Another regular source of food, during the breeding season, is the chicks of other birds. Frigatebirds will wheel in the sky above nesting seabird colonies, ready to snatch a chick that is left unguarded or wanders from a nest. Frigatebirds can even become cannibals by taking the young of other frigatebirds.


Breeding

Frigatebirds nest on islands, often sharing the colonies of other seabird species. The nest consists of a loose assemblage of sticks, usually at the top of a tree or bush but sometimes on the ground. The male frigatebird will choose a site and gather a few sticks which he will then sit on with his pouch inflated like a balloon. The idea is to attract a mate, who responds by bringing more sticks to add to the nest.

Once the single egg is laid, the male’s red pouch is deflated and returns to its orange colour. The egg will be well guarded during the six-week incubation period, as will be the chick when it hatches. Adult frigatebirds feed their chick for as long as eleven months in total, with both partners doing so for the first three months and the female taking over for the remaining eight. This long period of care, the longest of any bird, means that frigatebirds are not able to breed every year.

© John Welford