White-tailed Tropicbird ( Phaethon lepturus)

 

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Adult White-tailed Tropicbird (Photo by Andre F. Raine)

The White-tailed Tropicbird is the most widespread of the world's three tropicbird species, found in tropical and subtropical regions of all three of the world's oceans, except for the Eastern Tropical Pacific. In Hawaii it is found primarily in the Southeastern Hawaiian islands, with an estimated population of 1,500 breeding pairs, although that estimate is likely inaccurate. Although it has been found breeding on almost all of the Southeastern Hawaiian Islands, about half of the Hawaiian population breeds on Kaua'i, and only a few individuals breed in the Northwestern Hawaiian Island at Midway Island. The population at Midway only became established in the 1940's with the introduction of non-native Ironwood trees, which provided nesting habitat for the species.

On Kaua'i, White-tailed Tropicbirds breed in steep-sided valleys and sea cliffs throughout the island. They are easiest to see soaring around the cliffs at Waimea Canyon, the Na Pali Coast, and a few individuals at Kilauea Point National Wildlife Refuge, but they can be seen at almost any location on the island as they fly to and from their breeding sites in the interior. White-tailed Tropicbirds are also often seen from boats anywhere around the island and are quite often seen from shore. The species is common at all months of the year.

Adult White-tailed Tropicbirds are easily separated from adult Red-tailed Tropicbird by their smaller size, prominent black markings on the back and upper side of the wings, yellow green bill, and white tail. In particular, the black dorsal markings of White-tailed Tropicbird are often quite visible at a distance, and often from below when the bird is backlit. Also, White-tailed Tropicbird has white wing-tips that are usually distinctive when viewed from below. Juveniles of both species of tropicbirds have the dorsal surface extensively barred with black, and are quite difficult to distinguish. Note the smaller size and slightly broader black barring of White-tailed Tropicbird.

White-tailed Tropicbirds nest in a wide variety of locations, including shallow crevices in cliffs, forks in trees, rubble slopes, under bushes in sand dunes, and occasionally on human structures, such as buildings, open pipes, and quarries. The nest site is usually either a shallow depression, crevice, or other such shelter, and is usually smaller than that of a Red-tailed Tropicbird, which allows them to nest in a larger variety of places than that species. White-tailed Tropicbirds breed all year in Hawai'i, with a slight drop in numbers during the winter months.

White-tailed Tropicbirds are susceptible to predation at the nest by rats and mongooses, and habitat destruction by humans, volcanic erruptions, natural errosion. However, the populations in Hawai'i appear to be stable. Worldwide, the populations are not listed as threatened or endangered, although there are significant problems with harvesting of chicks and eggs at islands in the South Pacific and the Caribbean.