Introduction

Red-tailed Tropicbirds are the rarest of the three tropicbird species in North America, nesting in the Hawaiian Islands and dispersing widely across the central and south Pacific during the nonbreeding season. Individuals are sighted off the coast of California and Mexico on rare occasions. There are four large breeding colonies in the Hawaiian Islands (Kure, Midway, Laysan, and Lisianski) and one on Johnston Island to the southwest. Smaller groups breed on several other islands in the Hawaiian chain. Most of these islands are protected as U.S. Fish and Wildlife Service refuges, and the populations nest successfully in spite of some rat predation. Populations elsewhere are not as fortunate because humans and human-introduced predators take eggs, chicks, and adults, and destroy habitat.

This species nests colonially on oceanic islands, making its nest scrape in the shade of a shrub, bush, or tree, under tufts of grass, or in cavities on cliffs. A plunge diver that feeds solitarily, it does not depend on schools of predatory tuna that drive flying fish to the surface where they can be readily captured. Many other flock-feeding seabirds do need such concentrated prey.

Plumage and soft part colors of this bird do not vary appreciably throughout its range, although size varies significantly among islands—from smaller in the north Pacific to larger in the south Pacific. Males tend to be larger but birds cannot be reliably sexed from culmen, wing, or mass measures. The sexes are not otherwise dimorphic.

The three species of tropicbirds are unusual among the Pelecaniformes in these regards: they lay a splotched non-white egg, their young hatch downy, adults have a feathered gular region, nares are open externally, and adults put their bill down the chick’s throat to feed not visa versa. This species does, however, share the totipalmate condition (four toes connected by the web) with other members of its order.