Distribution

Abbott’s booby formerly bred on many islands in the Indian and Pacific Oceans (Bourne 1976; Stoddart 1981, 1984; Steadman et al. 1988). It is now confined to Christmas Island, Indian Ocean, at 10º25’S and 105º40’E. When breeding, it is thought to forage over open ocean northeast of Christmas Island, to Sumatra, Java, Tayandu, Kai and Aru Islands and Irian Jaya (Marchant and Higgins 1990).

Since the early 1900s Abbott’s booby has only been known to breed on Christmas Island, where it was first collected by C.W. Andrews of the British Museum in 1897 (Stokes 1988). The species may still occasionally range as far as the Chagos Archipelago, some 4000km west of Christmas Island (Hirons et al. 1976), where it probably formerly bred. Recent sightings in the Banda Sea south of the Moluccas (van Balen 1996) may indicate a more extensive foraging range than previously supposed. These latter sightings have led to speculation that a breeding population exists in that region (Cadée 1987; van Balen 1996), however, as van Balen notes, the booby is likely to routinely travel long distances from its breeding grounds. A recent specimen, found in a weakened condition on the Australian mainland near Broome, is thought to have been a vagrant.

On Christmas Island most nests are situated on the central and western areas, in the tall plateau forest, but they are also found along the north coast, in the upper terrace forest. Nest sites are largely restricted to areas above 150m, mostly on the sides of northwest facing slopes (Nelson 1978; Stokes 1988).

Habitat critical to the survival of the species

The sole breeding habitat, tall rainforest mostly above 150m elevation in the western, central and northern portions of the island, is critical to the survival of Abbott’s booby. Nearly all of this habitat is within Christmas Island National Park.

Abbott’s booby nests in tall, emergent rainforest trees in the deeper plateau and terrace soils of the western, central and northern portions of Christmas Island, mostly on the central plateau, 160-260m asl. Most nest trees are associated with uneven terrain created by gullies, hill-sides or cliffs.

Within suitable habitat, the location of nest sites is determined by the topography and nature of the canopy, resulting in a patchy distribution. Most nest trees are located in uneven canopy containing emergent trees, and nest sites are densest along crests of gullies and west-facing slopes (Nelson and Powell 1986). A variety of tree species is used, most often open-crowned Syzygium nervosum and Planchonella nitida, and Tristiropsis acutangula and Celtis timorensis where they become emergent (Nelson and Powell 1986; Reville et al. 1990b; Yorkston and Green 1992).

Abbott’s booby prefers nest sites on the lee side of slopes and gullies, with a clear area below and immediately downwind to facilitate take-off and landing. Southeast trade winds prevail between April and November and thus emergent trees that can be approached from the northwest are frequently used.