Red-billed Tropicbird
Red-billed Tropicbird

Common name: Red-billed Tropicbird, Boatswain Bird
Scientific name: Phaethon aethereus
Length: approximately 50 cm, wingspan of 1 m
Weight: 700 g (1.5 lb)
Population: approximately 7,500
Distribution: breeds in the tropics but can range well into temperate latitudes to feed
Issue: predation (adults, chicks, eggs), invasive species (rats, cats, dogs), fisheries (reduced food resources), tourism (disturbance of nesting sites)
IUCN Red List status: least concern

The Red-billed Tropicbird is one of three species in the family Phaethontidae, medium-sized seabirds with very long “retrices” (tail feathers). The Red-billed Tropicbird has mainly white plumage with, yes, a red bill. It has a black stripe extending from the bill, through the eyes and meeting at the nape. The “scapulars,” i.e., the feathers covering the bird’s shoulders at rest, have black bars. Females and males are the same size, but males have longer retrices.

It feeds on fish and squid, which it hunts by diving into the water. It also relishes flying fish. Its strong wings make it an energetic flier, flapping quickly rather than gliding. Spending most of its time at sea, it flies over the water looking for food. When it dives, its long, rigid tail stays out of the water. On land, however, the Red-billed Tropicbird is extremely awkward and must use its wings to crawl along on its belly.

Like many seabirds, the Red-billed Tropicbird breeds on isolated islands. It makes its nests on cliffs, rocks or among sparse vegetation. Outside of breeding season, it disperses widely out of its breeding range, even venturing into temperate regions (such as Nova Scotia or England). However, it is not considered a migratory species.

These birds breed year round in relatively compact colonies. The nests are sometimes a simple scrape on the ground and are defended aggressively. Females lay a single egg, which hatches after 43 days on average. When the juvenile fledges two or three months later, it is left to fend for itself by its parents. Birds acquire adult plumage at about three years old and begin to breed by about five years old. They can live as long as 17 years.

While populations in the Galapagos Islands and Cape Verde appear relatively stable, the Red-billed Tropicbird is not particularly abundant. Its total population is estimated at about 7,500 individuals. Invasive species—rats, dogs, and cats in particular—are a threat both to adults and to chicks and eggs. Overfishing, which removes fish from the oceans faster than they can reproduce, reduces the food available to this bird, which relies exclusively on the sea for its food resources.

The species does, however, have the advantage of a very large range, which gives it a certain resiliency to the numerous environmental pressures it faces. Nevertheless, the total population appears to be in gradual decline, and the species could well be classified as vulnerable in the years to come.

Did you know?
The two long tail streamers that characterize this family of birds play no role in its flight. Its function is purely ornamental and is used to court females. During the breeding period, males try to show off their spectacular retrices as much as possible in order to attract a female to mate with.

REFERENCES: Red List of Threatened Species of the International Union for Conservation of Nature (IUCN) and Encyclopedia of Life.

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