Tropicbirds are remarkable for being able to remain at sea for indefinite periods, and can sustain long periods of flight (3) (4). In the air these birds have a tern or pigeon-like flight pattern, with rapid wing-beats, although the tropicbirds also exploit their long wingspan and streamlined body shape to attain impressive altitudes by soaring upwards on rising thermals. While resting at sea, tropicbirds float on the sea surface, due to their fully waterproof plumage, and will take to the air again after powerful beats of the wings and thrusts of the fully-webbed feet (3).
The white-tailed tropicbird feeds largely on flying fish, but may supplement this diet with squid and crustaceans (2). Once its prey is targeted, it hovers briefly with the head and bill pointed downwards, before making a rapid, vertical, spiralling plunge from 15 to 20 metres (2) (3) (4). In the water, this bird can make rapid movements, with quick turns and twists, all the while using the half-bent wings to control its body, and its prey is captured in its serrated beak. Flying fish may also be caught in flight, and the white-tailed tropicbird may seek out fish that have been flushed by boats or, more rarely, shoals of hunting tuna. On land, however, this bird is less impressive and movement is extremely awkward. The bird lies on its belly and stabs its bill into the ground, pulling itself forward in an ungainly shuffle (3).
At sea, the white-tailed tropicbird is largely solitary, but during the breeding season, this bird may collect into loose colonies or small groups (2) (3) (4). Prior to breeding, monogamous pairs engage in unusual courtship displays, with up to 20 birds flying as high as 100 metres with ritualised wingbeats, dives and calls. The birds fly in unison, make wide circles and drop the tail and streamers in an arc, before pairs leave the group and perform a descending glide or zigzag in tandem (3) (4). Although not strictly territorial, there is fierce competition for the best nesting sites, and bloody fights between birds may ensue, with stabbing, slashing and the interlocking of bills (4). A nest is created by the male in a rocky crevice that offers some shelter from the sun, or less favourably on the ground (2) (3) (4). A single egg is laid and incubated by both the male and female at intervals of 13 days for some 40 to 43 days (2) (3) (4). Once hatched, the chick is largely left alone in the nest while the parents forage out at sea. It is at this time that the chick is most vulnerable to attacks, particularly from adults of the same or different species, which are looking for nesting sites (4). The single chick fledges after 70 to 85 days in the nest, and may join the adults in undertaking nomadic movements that see the birds wander as far as 1,000 kilometres out to sea in search of favourable feeding grounds (2). The white-tailed tropicbird first breeds between two and five, with most birds breeding in their third or fourth year (4).