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Gregory R. Mann, Ph.D. {ret.}

Red-tailed Tropicbird

“Phaethon rubricauda”

The Red-tailed Tropicbird is similar to the more common White-tailed Tropicbird but is bigger, with a pure white body, red bill and a very thin red tail which is not always visible in flight. Mature birds have mostly white plumage with a conspicuous black stripe from gape, curving towards and passing through eye. Their bill is strong, curved and bright red. Their legs and feet are blue-gray with webs distally black. Red-tailed Tropicbirds also have a red tail with long, red, central rectrices or tail plumes (36-55 centimeters). The species is also known by its Maori name “Amokura”. Their calls are a guttural squawk in varying intensities and/or high whistle-like screeches. They perform complex aerial courtship displays. Acrobatics consist of flying backwards, vertical displays and circles. Red-tailed Tropicbirds nest on the Hawaiian Islands and disperses widely in tropical and subtropical areas of the Indian & Pacific oceans; it occurs accidentally off southern California and along the California coast. It is more pelagic and is usually seen far out at sea.

Red-tailed Tropicbirds begin breeding after 4 years of age. Adults generally return to the same nest site each year. Nest sites are usually located in sheltered areas from the sun (base of a tree, in shrubs, next to a structure). The female lays a large single egg, ranging in color from reddish brown to purplish black, directly on the ground in the shade of vegetation, a log or rocks. Re-laying can occur if the first egg is lost or infertile. Incubation period varies from 39-51 days. Both parents incubate the egg. Average incubation shift lengths range from 8-9 days in some colonies. During the breeding season, the feathers of some birds take on a pinkish flush.  Adult Red-tailed Tropicbirds hunt alone and rarely fish within sight of land. They hunt by plunge-diving, wings half-folded, into the water to mostly catch flying fish, mackerel, dolphinfish, balloonfish and squid. Red-tailed Tropicbirds have weak feet and legs and thus, are poor swimmers and cannot walk well on land either. This makes them extremely vulnerable to terrestrial predators, such as rats, cats and pigs. The Red-tailed Tropicbird is very rare as a breeding species on the granitic islands, perhaps because it is unable to coexist with rats & cats or because of human persecution in the past. Red-tailed Tropicbirds spend most of their life far out to sea, except when they come in to land to breed. They have an average life-span of 16-years.

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