Australian Government Department of the Environment and Heritage, 2004
ISBN: 0 642 55078 6
Abbotts booby Papasula abbotti is a large, long-lived seabird, with the only known extant nesting colony on Christmas Island. Background information on the biology, population status and threats to the Abbotts Booby can be found at: http://www.deh.gov.au/biodiversity/threatened/recovery/list-common.html.
Abbotts booby is listed as Endangered under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). It is also a listed Migratory Species and Marine Species. The International Union for Conservation of Nature and Natural Resources (Hilton-Taylor 2000; IUCN 2001) and Action Plan for Australian Birds 2000 (Garnett and Crowley 2000) list Abbotts booby as Critically Endangered.
There are no estimates before 1967, but it is known the global range had been severely reduced by the early 1900s. By 1967, the breeding population was limited to Christmas Island and estimated at 2300-3000 pairs (Nelson 1971). Mining in the northwest sector of the island commenced in 1970, consequently scores of chicks, adults and their nest trees were destroyed by clearing (Powell in Yorkston and Green 1997). In 1979/80 and 1982, Powell and Tranter (1981) resurveyed the population and, although they did not estimate total numbers, found that the distribution of nests had not changed significantly from 1967, despite large areas of further clearance. The total breeding population in 1983 was estimated at 1900 pairs (Reville et al. 1990a), after an estimated loss of 400 breeding pairs since mining commenced in 1970. Mining ceased in 1987. In 1991, the most recent survey, the population was estimated at 2500 pairs (Yorkston and Green 1997). The difference between the two most recent published estimates was due to discovery of further nesting areas on the northern side of the island, and also among the southern and southwestern areas of distribution, but was not thought to indicate an increase in population size (Yorkston and Green 1997). Preliminary results from a 2002 helicopter survey suggest that the population is not showing signs of change.
Abbotts 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 10º25S and 105º40E. 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 Abbotts 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).
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 Abbotts booby. Nearly all of this habitat is within Christmas Island National Park.
Abbotts 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).
Abbotts 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.
The at-sea distribution of Abbotts booby is poorly known, and may contain habitat that is critical to the species future survival. Upwellings south of Java are thought to be important source of food for breeding boobies, but this is yet to be substantiated. To identify critical marine habitat, identification of the foraging range of Abbotts booby is desirable.
The distribution of Abbotts booby breeding sites in 1991 was mapped by Yorkston and Green (1997)(Fig. 1). Most sites were mapped accurately, according to the island grid surveyed for phosphate mining. The accuracy of some sites mapped earlier and a few areas away from the grid could be improved by remapping them according to a few points established by Global Positioning System. However, given that most of the breeding habitat is in the National Park, and hence already protected, accurate mapping of habitat critical to the species within the park should be a low priority action.
Although most Abbotts booby habitat is within the Park, its limited extent makes long-term protection of quality habitat outside the Park a desirable goal. Recommendations of the draft Conservation Management Plan for Terrestrial Wildlife on Christmas Island outside the National Park (Dexter 2002) include assessment of the ecological quality of primary rainforest outside the Park and mapping of habitat that fits the criteria of habitat critical for endangered species.
A more recent helicopter survey identified a significant cluster of nesting Abbotts boobies outside the Park. Given this and the proposal by Phosphate Resources Ltd (PRL) to undertake surface mining, transport and off-site processing of phosphate at nine sites (EPBCwhich the Minister for the Environment and Heritage has declared must be assessed, mapping of important Abbotts booby habitat on Crown Land and other jurisdictions outside the Park would be invaluable.
The only known extant breeding population of Abbotts booby is on Christmas Island, Indian Ocean. Conservation of this population is therefore essential to the survival of the species.