White-tailed Tropics - Mint Set

This species, also known as the Yellow-billed Tropicbird, co-exists with the Red-billed Tropicbird on Ascension where it is approximately twice as abundant as its larger relative.

It has been observed that the moulting of the flight feathers of Ascension’s sea birds and breeding rarely occur at the same time. This is most probably due to the nutritional requirements of replacing feathers and the decreased flight efficiency during moulting. Whereas most of the sea birds of Ascension demonstrate synchronised annual breeding, the White-tailed Tropicbird is able to complete its cycle of breeding and moulting within 38 weeks and this appears to determine the minimum interval between successive breeding attempts. Spending their lives either breeding or replacing their plumage, individuals arrive to breed throughout the year (although they usually meet up and breed with the same mates).

Prior to developing their familiar black and white feathers, the White-tailed Tropicbird chicks have white downy feathers. The Red-billed and White-tailed Tropicbirds compete for nest cavities in the cliffs around the island, often under boulders or in narrow rock crevices (as shown on the 35p and 40p values). They lay a single egg that can vary from pale fawn to a rich purple brown and averages 54 x 38mm in size. Incubation takes approximately 40 days and chicks leave the nest when they are around 75 days old.

White-tailed Tropicbirds are in all dimensions smaller than the Red-billed. Their chicks are half the weight on leaving the nest and this difference in weight is maintained at equivalent stages throughout adult life.

Juvenile tropicbirds of both species are difficult to differentiate but young White-tailed Tropicbirds tend to have heavier dark barring. Juveniles (as shown on the 50p value) lack the long tail feathers and have heavy black barring on the upper-parts.

Apart from the noticeable size difference (39cm or 76cm including central tail feathers compared to 48cm and 100cm) adult White-tailed Tropicbirds (£1.25 value) are similar in form to the Red-billed Tropic species, but have prominent black diagonal bars on the wings.

Like all tropicbirds, they eat fish and squid by hovering and then plunging vertically into the sea. They eat crustaceans in a higher proportion than the Red-billed Tropicbird and occasionally catch flying fish. Flights are also similar to those of the Red-billed Tropicbird, with bursts of rapid wing beating alternating with glides in which the wings are often held high and the tail depressed. Calls are less shrill and have a chuckling quality.

A recommended site to see White-tailed Tropicbirds is Boatswain Bird Island, Ascension Island.