Frigatebirds are often called the pirates of the sea, because they rob other birds – such as boobies – of their catches, snatching the fish just as they return to the surface! This blue-footed booby (below) shows how easy it would be for a frigatebird to snatch a fish – luckily for this bird, there were none around!
In spite of this behaviour, frigatebirds obtain most of their food by direct capture, i.e. snatching prey such as flying fish, or floating squid, off the surface of the sea. They are also nest robbers, capable of swooping down and stealing eggs and young from nesting sea birds such as terns and petrels.
Frigatebirds are superbly adapted to soaring and gliding over the oceans of the world, sometimes hanging on the wind and keeping station above boats and ships. The updraft from a moving ship provides an ideal ‘platform’ for them to patrol the sea with little expenditure of energy!
Some of the juvenile birds appear to prefer sitting on the ship rather than gliding!
Frigatebirds usually forage alone like this single male (below), or in pairs, but larger aggregations occur nearer to the breeding colony or where there is an abundant source of food, such as behind fishing boats. It is said, that frigatebirds have the largest wingspan-to-body weight ratio of any bird, and when they soar above ships they really do look like living hang gliders!
The males have brownish-black, iridescent plumage, long narrow wings and a deeply forked tail. On the ground, the males can be separted by the colours of their long back feathers, which are a shiny bottle-green colour in the great frigatebird and purple sheen on the magnificent. The females of both these species of frigatebird are slightly larger than the males and have white breasts and undersides.
I took all of these photographs in The Galápagos. The aerial shots were taken on board the MS National Geographic Endeavour. We visited a mixed colony of nesting frigatebirds on North Seymour Island, next to Baltra. Two species of frigatebirds nest on North Seymour Island in The Galápagos: Great and Magnificent. The magnificent frigatebird (Fregata magnificens) is the biggest, with a wingspan of up to 245 cm. The slightly smaller great frigatebird (Fregata minor) has a wingspan up to 230 cm but the males are almost impossible to separate in flight. The scarlet gular pouch of the males is inflated during breeding – it is certainly a good way of attracting the attention of the females! The sac is even partially inflated when the male is resting (below).
The trail on North Seymour passes through the frigatebird colonies where the birds nest on low saltbush trees.
Breeding is quite a protracted affair in frigatebirds. It takes about 40-55 days for the eggs to hatch and a further period of up to 7 months before the offspring have fledged. The adults are often absent for up to three days searching for food, so the chicks grow slowly and are used to waiting around a long time for the next meal!
There is also a long period of post-fledging care which can last for up to a year. The juvenile birds hang around the nest like typical teenagers (!), waiting for the odd scrap or begging for a free meal from the parents. This lengthy period of care means that a female can only breed every two years, or longer, whereas the males can in theory, breed every year (assuming they can find another mate). This pattern of males breeding annually and females biennially is said to be unique in birds (1).
The female magnificent frigatebird is easy to identify by her blue eye-ring (above and below). The eye-ring is red in the female great frigatebird.
Frigatebirds are often seen ‘sunbathing’ with their wings outstretched, as above. In fact, this posture is thought to be a way in which they cool down, losing heat by exposing the warm underwing and dissipating heat by convection (1).
Frigatebirds have a fearsome reputation, partly deserved, but they are magnificent organisms, successful and adaptable. They patrol the tropical oceans of the world and have learnt how to take advantage of Man’s activities, by following fishing boats and feeding on scraps and discards. There are five species; two are rare or endangered: Ascension and Christmas Frigatebirds. The other three species (Magnificent, Great and Lesser) are however, not globally threatened and are thought to number several hundred thousand birds, each.
1) Family Fregatidae (Frigatebirds). Handbook of the Birds of the World. Volume 1. pp. 362-374. Lynx Editions 1992.