Tropic-birds

Tropic-birds were once thought to belong to the Pelecaniformes order that includes pelicans, cormorants, boobies and frigate-birds. However, it is now generally agreed that this classification is wrong and they must be assigned their own order which has been designated the Phaëthontiformes, with the three tropic-bird species belonging to a single family, the Phaëthontidae. The three species are the red-tailed tropic-bird (Phaëthon rubricauda), white-tailed (or yellow-billed) tropic-bird (Phaëthon lepturus) (see picture) and red-billed tropic-bird (Phaëthon aethereus).

As the name suggests, tropic-birds rarely stray beyond the Tropics. They are pelagic birds that spend virtually their whole lives at sea, only coming to land to breed. All three species are found in the Pacific and Indian Oceans, but only the white-tailed and red-billed are seen in the Atlantic Ocean.


Appearance

The largest tropic-bird species is the red-billed, at 24 inches body length, with the white-tailed measuring 16 inches and the red-tailed 19 inches. However, they all have long tail streamers that double their overall length. The streamers resemble marlin spikes, which is why sailors have traditionally named them “bosun’s birds”. The wingspan is between three and four feet.

The bodies of all three species are generally white with black markings on the head and wings, plus the distinguishing features that give each species its name. Young birds lack tail streamers in their first year and their plumage is barred with black.


Behaviour and feeding

The sight of a tropic-bird at sea can be very surprising, as they seem to appear out of nowhere, hundreds of miles from land. A tropic-bird can fly 50 to 100 feet above a ship or boat, circle it a few times giving a sharp cry or two, then fly away again.

Tropic-birds feed on fish and squid, which they take by diving from a height of 50 feet or more. A bird will hover for a short time before diving with wings half-closed, in a similar manner to a gannet. After plunging in it will reappear after a few seconds with its prey in its beak, then take off from the surface, eating its meal as it goes.


Breeding

Tropic-birds lay a single egg on a cliff ledge or may do so on the ground under a shrub on a low-lying island, or in a hole. No nest is constructed. Incubation takes 28 days, with both parents taking turns, and the chick will take as long as 60 or 65 days to fledge. The parent birds will therefore spend nine months of the year at sea and the other three on land. However, a second brood may be raised, which means that some tropic-birds can divide their time equally between land and sea.

When fledged, the young tropic-bird is on his or her own, as the parent birds will desert the youngster at this stage. He or she will spend much of their life in isolation, although pairs do often stay together at sea. It is only during the breeding season that tropic-birds are seen together in any numbers, especially where is competition for nesting sites. Tropic-birds mate after a courtship display in which up to 20 birds may take part, the main feature being a circling flight, up and down, in which the tail streamers are waved to attract attention.

Tropic-birds will guard their egg zealously, even to the extent of not moving until physically lifted off it, although they will complain vociferously before and after this happens. South Sea Islanders are thus able to collect tail streamers by plucking them from the birds without otherwise harming them.

Man is still the main enemy of the tropic-bird, with egg collection being the main threat. However, the tropic-bird is a protected species in many areas where it nests, so populations that were once in decline have made a comeback.

© John Welford