Introduction

Adult Red-tailed Tropicbird, Hawaii, March

Figure 1. Breeding range of the Red-tailed Tropicbird in the Hawaiian Islands and nonbreeding marine range.

Red-tailed Tropicbirds, first described by Boddaert (1783) from Mauritius, 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 Atoll 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.

Several studies have examined the general breeding biology of the species. Fleet (1974) studied breeding biology on Kure Atoll from 1964 through 1965, Diamond (1975) on Aldabra for 15 months, 1967-69. The authors conducted research on breeding biology and ecology of the species for 20 years on Johnston Atoll and Christmas Island (published herein and Schreiber and Schreiber 1992, Schreiber et al. 2001, Doherty et al. 2004, Schreiber et al. 2004). Spear and Ainley (2005) published data on the behavior of all three tropicbird species at sea.