Distribution and population sizeDistribution and population size

Distribution and population size

The Christmas Island Frigatebird breeds only on Christmas Island, a volcanic island in the Indian Ocean (10o0'S; 105o40' E), approximately 1400km northwest of Australia. The island sits on the northernmost edge of the Australasian continental plate, and immediately north the ocean floor drops into the Java Trench and depths of up to 6000m. The nearest land is Java in the Republic of Indonesia, which is 360km to the north. Christmas Island is truly oceanic and all its biota has colonised by sea or by air (Gray 1981). Christmas Island is 135km2 and 75% is covered with original vegetation (Environment Australia 2002).

When not breeding, Christmas Island Frigatebirds range widely around South-east Asia and the Indian Ocean, and are occasional visitors to the shores of Java, Sumatra, Bali, Borneo, the Andaman Is, Darwin and the Cocos (Keeling) Islands (Gore 1968, Marchant & Higgins 1990). It is possible the young birds are nomadic and wander widely until they reach breeding age, however, adults have also been seen far away from the island. It has been speculated they may breed somewhere in the Anamba-Natuna islands (Chasen 1933, Gibson-Hill 1947), but this was based only on sightings in the vicinity of these islands.

Three modern nesting colonies are known on Christmas Island: the golf course, cemetery and dryers colonies (Figure 1). Stokes (1988) reported that the golf course colony covered c. 40 ha, the cemetery colony c. 65 ha, and the dryers colony c. 66 ha.

Gibson-Hill (1947) estimated the total breeding population to be 1000-1500 pairs. In 1972, the population almost certainly numbered fewer than 2000 pairs (Nelson 1972), and in 1975 it was claimed to comprise fewer than 1000 pairs and to be declining (Nelson 1975). The most recent estimate was of 1620 pairs (Stokes 1984). All the above figures except Stokes (1988) were not based on surveys. The Stokes estimate was based on a three-year count of nests in the golf course colony and estimations of the number of nests at the other two sites (T. Stokes pers. comm.). A census of nest sites in the golf course colony in 1985 revealed that it contained c. 854 occupied nests during the time of peak nest numbers in June/July (Stokes 1988). There is no historical or current census data on the numbers of nests in either the cemetery colony or the dryers colony, although it is possible the dryers colony may no longer be used for nesting (see Threats section). Further data is required on the habitat requirements for Christmas Island Frigatebird breeding and on the use of all nesting colony areas.

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