The three species of tropicbird all have tropical distributions. Two species are found in the tropical Atlantic and both breed on Ascension Island, with the majority of both species breeding on Boatswainbird Island. The most numerous is the Yellow-billed Tropicbird, or Boatswainbird (so called because its call is likened to that of a Bosun\’s whistle) after which the island was named. About 500 pairs of Red-billed Tropicbirds breed on Ascension.
The Red-billed Tropicbird is a powerful bird around 48cm long (up to 100cm including the central tail feathers) and with a wingspan of 105cm. It is a white bird with black near the wing-tips, fine dark grey barring over the back and with two long trailing tail feathers. The bill is long, strong and red (yellow in juveniles as can be seen on the 90p value) and the legs are yellowish.At sea the flight is strong and direct, resembling a pigeon, but when seen from land the birds are generally making repeated and hesitant approaches to nest sites.Courtship flights can also be seen where several birds alternate rapid flapping and dramatic glides, accompanied by chuckles and screams (giving rise to the name Boatswainbird).
Like all tropicbirds they feed on fish and squid by hovering and then plunging vertically into the sea, although they are poor swimmers.They nest in crevices in the rocks and where these are in short supply fighting, sometimes to the death, is common. The single egg is fawn to rich purple and averages 64 x 45mm. Incubation lasts around 43 days. Both parents incubate and shifts can last several days.The birds spend the non-breading season far out to sea, undergoing a complete moult before returning to land.