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Executive Summary

The Christmas Island Frigatebird is the rarest endemic seabird on Christmas Island and is listed as Vulnerable under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). In Australia, it is confined to Christmas Island where it breeds in terrace forests in only three small areas totaling about 170 ha in extent. The total population size, last estimated in the early 1980's was approximately 1620 pairs. Limits to total population size are unknown, however considerable areas of former breeding habitat have been cleared and the species was likely more numerous prior to this loss of habitat. Breeding areas of the Christmas Island Frigatebird are now threatened by the invasive Crazy Ant. These ants potentially threaten individual breeding birds as well as the nesting trees. Crazy Ants pose an imminent, extreme risk to the conservation of this and all Christmas Island birds. Much of the breeding colony areas of the Christmas Island Frigatebird lie outside the national park and do not have any formal protection. Other threats to the conservation of Christmas Island Frigatebirds include past pollution from phosphate mining, which has affected one nesting area, and the risk of catastrophic destruction of breeding colonies by wildfires or cyclones.

Background Information

• Conservation Status
• Taxonomic Status
• International Obligations
• Distribution and population size
• Biology
• Diet
• Habitat Critical to Survival
• Social and economic impacts
• Biodiversity Benefits
• Relationship to other plans

Conservation Status

The Christmas Island Frigatebird Fregata andrewsi is the rarest of the five species of the family Fregatidae and breeds only on Christmas Island. It is listed as Vulnerable (ICBP 1981, Garnett 1992, EPBC Act) (B1, C2b), however Garnett & Crowley (2000) recommended it be considered Critically Endangered (A2c, e, B1, B2bce) due to the inferred impact of the Crazy Ant.

Taxonomic Status

The Christmas Island Frigatebird is one of three frigatebird species which breed on Christmas Island. The Greater Frigatebird (F. minor) is much more common on Christmas Island and has a much wider breeding distribution. The Lesser Frigatebird (F. ariel) was only recently discovered nesting on the island.

International Obligations

The Christmas Island Frigatebird is listed on the Japan-Australia Migratory Bird Agreement (JAMBA) and the China-Australia Migratory Bird Agreement (CAMBA).

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.

Biology

Frigatebirds are a group of seabirds that are adapted morphologically for a highly specialized type of aerial feeding which affects their entire breeding ecology and behaviour. All have extremely prolonged breeding cycles. Frigatebirds in general, do not remain faithful to the same mate or nest site from year to year. Each new breeding effort involves setting up a new territory/nest site, and finding a new mate (Nelson 1975). There is no information on the nest site or mate fidelity of Christmas Island Frigatebirds, but they are probably similar to other frigatebirds.

It requires at least 15 months for a pair of Christmas Island Frigatebirds to raise one offspring to independence, although it is not known whether both partners are required for the entire period. Both Greater Frigatebirds and Lesser Frigatebirds share parental duties and only raise one offspring every two years. However, Magnificent Frigatebird (F. magnificens) males cease parental duties when the young are three to four months of age, leaving the females to raise the young to independence. As a result, males breed every year and the females every second year, and there is a skewed sex ratio (Diamond 1972). In Christmas Island Frigatebirds, females tend to feed the older juveniles more than males do (Gibson-Hill 1947, Marchant & Higgins 1990), but males have been recorded feeding free-flying young that were at least eight months old (Nelson 1975). Thus, it is not known whether male birds can attempt to breed annually. The sex ratio of Christmas Island Frigatebirds is not known.

At the beginning of each breeding season, adult males select sites from which they display to females. Males begin displaying in late December and begin forming pairs in late February (Marchant & Higgins 1990). The nest is built on the display site after a male has attracted a female (Nelson 1975). As many as 30 nests have been recorded in one tree (Nelson 1975; T. Stokes, pers. comm.).

Most young hatch between mid April and late June and are extremely slow-growing (Nelson 1975), but appear to grow more rapidly than other frigatebirds (Nelson 1972). Young frigatebirds first take to the air when the are c. 6 months old (Nelson 1975, Marchant & Higgins 1990), but remain dependent on the parents for at least a further 9 months (Nelson 1975). This extended period of dependence effectively means that the breeding cycle is biannual, since the time from laying to independence is approximately 15 months. Thus probably only about half of the adult population lay each year (Stokes 1988). Young birds attain adult plumage in the beginning of their fourth year (Gibson-Hill 1947) and the age of first breeding of frigatebirds, in general, is at least five to seven years, possibly older (Nelson 1975); it may even be as much as 9-10 years (Croxall & Rotherby 1991).

Probably 15 to 20% of eggs laid yield fledged young. However, Nelson (1975) found that Christmas Island Frigatebirds appeared to be more successful than other frigatebird species. Some groups on Christmas Island were able to successfully raise 60% of nestlings to at least half grown, but overall c. 30% at most reached fledging age; some groups had lower than 20% success (Nelson 1975). Probably no more than 20 to 30% of frigatebirds die during their first year of independence (Nelson 1975). It is likely that it takes a breeding pair at least 20 to 25 years to replace themselves. This would make recovery of population numbers from any decline extremely slow.

Nelson (1975) speculated that frigatebirds, in general, probably have an adult mortality rate of about 4% p.a., giving them an average life expectancy of about 25.6 years. He reasoned that some individuals probably live to 40 or 50 years.

Diet

Christmas Island Frigatebirds forage either by scooping up marine organisms or offal floating on the surface of the water or by their piratical habit of harassing other seabirds forcing them to disgorge some of their meal. Their main food is probably flying fish and squid (Gibson-Hill 1947), however they will occasionally take food off land, pick up carrion and offal from beaches, and steal eggs and nestlings. Grasshoppers have also been recorded from stomach contents (Marchant & Higgins 1990). Most nesting adult frigatebirds appear to forage in the waters immediately around the island. Young birds that have not yet reached breeding age and non-breeding adults probably forage much farther afield.

The waters surrounding Christmas Island may be unusually productive. Christmas Island Frigatebird nestlings were fed more frequently than Greater and Lesser Frigatebirds on other islands and grew much faster (Nelson 1972, 1975). Studies of Abbott's Boobys suggested that food availability in the waters surrounding the Christmas Island fluctuate greatly from year to year (Reville at al. 1990).

Habitat Critical to Survival

Christmas Island Frigatebirds can experience great difficulty in becoming airborne and cannot take off from perches less than 3m from the ground (Gibson-Hill 1947). During most of the year the prevailing wind on Christmas Island is the south-east trade winds, and nests are sited preferentially in the lee of the wind or protected (Stokes 1985). Frigatebirds nest under the top branches of trees and require a site that is calm enough to allow them to land safely. In 1994 a few appeared to nest in one or two trees high up the cliff above the road to Smith Point in Flying Fish Cove (A. Dunn unpubl. data). Nelson (1975) noted that they prefer to nest in Sea Almond Terminalia catappa. A survey of the golf course colony in 1983 found that the two species T. catappa and Celtis timorensis comprise 65.5% of all nest trees chosen (Stokes 1985). Ficus sp. trees are also often used for nesting (Marchant & Higgins 1990), but are rarely used in the golf course colony (Stokes 1985). These nest tree species occur right around the island and yet the species nests only in a small area of the island.

Data collected in the mid 1980s by T. Stokes may provide better characterisation of preferred nesting habitat. Analysis of this data is underway. Christmas Island Frigatebirds appear to be more restricted in their choice of nest sites, tending to nest well down on the shore terrace (Gibson-Hill 1947, Nelson 1972), whereas Greater Frigatebirds will also nest on the slope or lip of the inland cliff or higher up on the terraces (Gibson-Hill 1947).

Given the limited data on habitat requirements, habitat critical to survival of the Christmas Island Frigatebird is defined as all nesting areas. The approximate boundaries of the nesting colonies are given in Figure 1. Sympathetic management of areas adjoining nesting colonies may be very important. Abbott's Booby nesting colonies within 300m downwind of cleared forest have been shown to have significantly lower breeding success than colonies upwind of the cleared areas (Reville et al. 1990), and it is highly likely a similar result would be found for Christmas Island Frigatebirds. Increased wind turbulence around Christmas Island Frigatebird nest sites is a cause for concern. Applying a precautionary approach given the available information, clearance of vegetation within 300m of nesting colonies should be considered undesirable. Actions proposed in this plan will help to better define habitat critical to survival of the Christmas Island Frigatebird, including whether the dryers colony is still viable nesting habitat.

Social and economic impacts

The actions in this plan may have positive and negative social and economic impacts. Positive social impacts will arise from community education actions that will increase Christmas Islanders knowledge and interest in their own environment. The rainforest rehabilitation program provides on-island jobs, as will the proposed frigatebird monitoring program. Christmas Island endemic birds attract specialist bird watching groups each year which is high value, low-impact tourism.

Negative social and economic impacts arising from implementation of the plan could include greater restrictions due to review of the quarantine barrier. The EPBC Act already provides a regulatory framework for the protection of rainforest on Christmas Island, and one element of this is assessing potential impacts of proposed developments on the listed threatened species. These provisions have the potential to impact on economic activity, for example by adding additional obligations to industry and other development on the island in order to minimise impacts on listed species. This arises from the listing of the species under the EPBC Act invoking a range of protective provisions and offences where a population is to be affected. The magnitude of this potential impact is unknown, as it will vary with the location, size and extent of the activity, proposed or current. However, the recovery plan will aid in determining what could be significant impacts on the Christmas Island Frigatebird (through defining habitat critical to survival and developing a management plan outside the national park).

Biodiversity Benefits

Protection of the habitat of the Christmas Island Frigatebird provides protection for numerous other listed species, including those in Table 1. Community education targeted at this species will promote awareness of all the endemic birds and their conservation needs.

Notes: (e)=species or subspecies endemic to the island.
E Listed under the EPBC Act as Endangered
V Listed under the EPBC Act as Vulnerable
M Listed under the EPBC Act as a Migratory species
MF Within a family listed under the EPBC Act as Migratory
S Listed Marine species under the EPBC Act.
C Listed under CAMBA
J Listed under JAMBA

Relationship to other plans

The National Park Management Plan is the strategic nature conservation document for Christmas Island. This recovery plan makes numerous recommendations in common with other recovery plans for Christmas Island threatened taxa. Opportunities for sharing resources and points shared in common with other recovery plans are identified in the implementation section of this plan.