Section Distribution - National Recovery Plan for the Cocos (Keeling) Islands Buff-Banded Rail (Gallirallus philippensis andrewsi) - Distribution | Zoe
National Recovery Plan for the Cocos (Keeling) Islands Buff-Banded Rail (Gallirallus philippensis andrewsi)
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Located in the Indian Ocean (lat. 12° 12’S, long. 96° 54’E), the CKI are approximately 2900km north-west of Perth, 975km west-south-west of Christmas Island and 1,000km south-west of Java Head. They are an Australian Offshore Territory, comprising 27 separate islands (Fig. 1), 26 in the Southern Atoll, and North Keeling Island, located 24km to the north (lat. 11° 50’S, long. 96° 49’E). North Keeling Island, also Pulu Keeling National Park, is an internationally renowned seabird rookery and is listed as a wetland of international importance under the Ramsar Convention. A true coral atoll, North Keeling Island is low and flat with a large interior lagoon recently disconnected from the sea. Six main vegetated habitats can be recognised (after Gibson-Hill 1948; Williams 1994): tall Pisonia (Pisonia grandis) forest; tall Coconut (Cocos nucifera) open palm forest; lagoon fringing low forest of Ironwood (Cordia subcordata); patches of lagoon fringing shrub-thickets of Teabush (Pemphis acidula); a coastal, thin coralline strandline of low herbs; and patches of lagoon fringing herbland comprising grasses, sedges and Sea Purslane (Sesuvium portulacastrum), with admixtures of Pisonia-Coconut Palm and Pisonia-Ironwood forests. Octopus bush (Argusia argenta) is a common small tree of the sea coast at the edge of Pisonia-Coconut Palm stands, and Cabbage Bush (Scaevola taccada) is a patchily common shrub on forest margins. The CBBR utilises all habitats equally and occurs throughout North Keeling Island (Reid 2000), even foraging occasionally in the intertidal zone and to venture into shallow rock pools to bathe (Reid & Hill 2005). Up to 40 birds at one time have been seen foraging on the lagoon shore, and this seems to be a preferred feeding habitat (Hopton 2003; Reid & Hill 2005).
Habitat critical to survival
North Keeling Island is the habitat critical to survival of the CBBR. This island is managed as a National Park and is free of the threatening processes that led to the extirpation of this species from the Southern Atoll. Surveys have shown that CBBR uses all habitats on North Keeling Island. It is the geographic isolation of the island, naturalness of the habitats, abundance of breeding seabirds and lack of introduced predators that allow the CBBR to survive at high densities.
Figure 1: Cocos (Keeling) Islands
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Threats
Single, small isolated population Small isolated populations are threatened by stochastic extinction through genetic or demographic failure and environmental disaster (such as cyclone, tsunami, severe drought). The current population is sufficiently high for the risk of extinction though genetic or demographic stochastic events to be low. The risk posed by environmental catastrophe (either killing the birds directly or depletion of food sources) also appears low, as the population has survived numerous such events, most recently Tropical Cyclone Walter in April 2001. Although a low risk, contingencies against environmental disaster must be considered, as extinction of small island bird populations by intense storms has occurred (Simberloff 1994).
None of the threats below may have singly led to the extirpation of the CBBR from the Southern Atoll. Rather, a combination is suggested. The North Keeling Island population is not currently exposed to any of these threats but most exist on the larger islands of the Southern Atoll.
Habitat Modification In the early 1800s the vegetation on the Southern Atoll was largely converted from indigenous forest to coconut plantation monoculture. The coconut plantations maintained an open understorey for ease of collecting coconuts until commercial operations ceased in the late 1970s. Since then the understorey has thickened with a large build up of fallen coconuts, young emergent plants and patches of thick cabbage bush creating dense thickets. It is unknown whether the open understorey of the managed plantations created more suitable habitat for the CBBR than current conditions. However, the dense overgrown habitats now may be habitable for rails, as it is commonly used for cover by two introduced ‘rail-like’ pheasant species, the Green Junglefowl (Gallus varius) and feral individuals of the Red Junglefowl (G. gallus), and by the recently self-established rail, the White-breasted Waterhen (Amaurornis phoenicurus) native to Indonesia – see Reid & Hill (2005).
Reid (2000) suggested that the loss of a large multi-species seabird rookery from the Southern Atoll probably would have resulted in a lower carrying capacity of the Southern Atoll and led, in part, to the eventual demise of the CBBR population. Cushman (1995) and Polis et al. (1997) had established that marine inputs of organic carbon and nutrients, via seabirds’ use of small islands for nesting, contributed greatly to such islands’ food-web budgets, with benefits (additional food and nutrition) flowing to all parts of the food chain. For detritivores and occasional predators of seabird nests, like CBBRs (Marchant & Higgins 1993), the benefits are obvious, and an association between the rails and seabird colonies has been noted before (Schodde & de Naurois 1982). This hypothesis can be tested with the planned reintroduction of CBBR, in that population densities would not be as great in the absence of breeding seabirds under the assertion. Ideally, habitat restoration though selective clearing of undesirable plants and revegetation would be implemented, with the eventual supplementary aim of restoring breeding habitat on the Southern Atoll for forest-nesting seabirds.
Cats (Felis cattus) Cats are known to prey upon CBBR. The last individual definitely found on West Island was probably killed by a domestic cat in 1991 (Stokes 1994). Cats are assumed to have been introduced by early settlers (Algar et al. 2002). They were not mentioned as a threat to bird populations by Gibson-Hill in the 1940s (Gibson-Hill 1949), but were noted as such in the 1970s and 1980s (e.g. Stokes et al. 1984). The persistence of CBBR on the Southern Atoll for approximately 150 years in the presence of cats indicates that predation by cats was not the lone factor leading to the demise of the rail. However, any undue pressure on small populations has a large effect. Increases in cat numbers often coincides with increases in human population, especially with an increases in food waste, as may have occurred with changes to land use and administrative arrangements during the 1970s (when a large mainland Australian population was established on West Island).
Cats are thought to have played a significant role in the extirpation of CBBR from West Island. Cats are currently known to occur on three islands on the SA, namely West Island, Home Island and South Island (Algar et al. 2002). The CKI Shire Council has been running a feral cat control program on West and Home Islands since 2000 and these efforts have considerably reduced the number of feral cats, at least for short periods. The threat has not been eliminated and the control program is continuing. Surveys conducted by Algar et al. (2002) found no evidence of cat presence on the other islands on the SA and no cats occur on North Keeling Island. Complete eradication of cats from any SA island targeted for reintroduction should occur prior to any translocation.
Rats (Rattus sp.) The threat posed by rats primarily is the predation of eggs and young birds, and potentially competition for invertebrate food. Although there is currently no direct evidence that rats preyed on CBBR, they are known to prey on the eggs and chicks of a wide range of smaller seabirds and land birds, and particularly on rails on isolated islands (Steadman & Martin 2003). Rats have been implicated in the extinction of five endemic forest bird species and the decline of a number of other birds on Lord Howe Island, impacted two species of seabirds and four forest species on Norfolk Island, directly impacted six species of seabirds on Macquarie Island, and have eradicated breeding populations of two species of noddy (Anous spp.) on Bedout Island (Anon. 2005). Rats were believed to have played a role in decline of birds on the Southern Atoll of the CKI by both Gibson-Hill (1949) and Stokes et al. (1984).
Black Rats (R. rattus) are known to be present on most islands of the Southern Atoll, but are not currently on North Keeling Island. Brown Rats R. norwegicus), although not listed as being present on the Southern Atoll by Gibson Hill (1948), had been recorded earlier by mammalogist, Wood-Jones (1909). In the absence of recent definitive studies, the presence of Brown Rat should not be ruled out. Complete eradication of rats from any Southern Atoll island targeted for reintroduction should occur as part of a reintroduction program and prior to translocation.
Red Junglefowl (Gallus gallus) and Green Junglefowl (G. varius) (feral chickens) Two species of introduced chicken occur on the Southern Atoll. The Red Junglefowl occurs on virtually all islands and is kept domestically, both free ranging and enclosed by residents. It is less common on West Island where the Green Junglefowl was introduced and has successfully established a large population. Junglefowls and the CBBR are ecologically very similar, particularly in their ground-foraging habit, dietary catholicism, food items, and manner of feeding. Combined with habitat modifications and the loss of seabirds from the Southern Atoll islands, the ecosystem may not be able to accommodate two species sharing similar niches, with the larger junglefowls likely to be the more successful competitor. The eradication of feral chickens would be required before any reintroduction of CBBR.
Hunting by humans In the past Cocos Malay people hunted and ate CBBR (Gibson-Hill 1949). However, CBBR were rarely taken when other seabird species such as the Red-footed Booby (Sula sula) were available. The CBBR is thought not to comprise a major part of the diet of the Cocos Malay people in recent decades. Hunting of the CBBR, specifically, is not considered an important Cocos Malay cultural tradition (as some community members see booby hunting), and therefore this threat is not likely to exist currently (Noor Anthony, personal communication). The CBBR remained on the Southern Atoll under human hunting pressure for many decades after many of the seabirds such as boobies were hunted to local breeding extinction.
Objectives, Performance Criteria and Recovery
Overall Objective
Secure two viable populations of the CBBR on the Cocos (Keeling) Islands.
Specific Objectives
Maintain a viable and secure population on North Keeling Island.
Secure abatement of all major threats on the island targeted for reintroduction in the Southern Atoll.
Establish a second viable population to prevent total extinction through a catastrophic event at North Keeling Island.
Develop community support for and involvement in the recovery of the CBBR in the CKI.
Encourage significant threat reduction over other islands in the Southern Atoll to provide additional habitat for dispersing CBBR.
Performance Criteria
Regular park surveillance by Parks Australia North (PAN) has ensured that North Keeling Island biodiversity security is not breached.
Transect-based sampling on North Keeling Island shows the population is maintained at greater than 700 individuals.
Adoption of a Translocation Proposal, after independent review, in the first 12 months.
Within 12 months all rats, cats and chickens eradicated from the island targeted for reintroduction.
15 ha of habitat on the reintroduction island restored, revegetated and maintained within five years.
Methods for monitoring re-introduced birds using radio-telemetry established and baseline movement data collected using North Keeling Island CBBR within 18 months.
20 CBBR reintroduced to an Island in the Southern Atoll within 2.5 years.
The CKI community are actively involved with all stages of CBBR recovery, through voluntary and paid employment activities, and an education/training component through school activities (classes and education materials); and have received information related to the program (broadsheets, informal communications). A ‘CBBR Wildlife Ranger’ position established within the CKI Shire Council, dedicated to implementation of the CBBR Recovery Plan, ensuring local community involvement and interest. Integration of CBBR recovery activities with any proposed eco- and culture-based tourism developments will also be a measure of greater community and Council involvement and support.
Within 5 years transect-based sampling of the reintroduced population of CBBR shows the second population has been established and is maintained at greater than 50 individuals.
No feral animals detected on the island for reintroduction, or if detected removed within 1 month.
Performance of the plan will reviewed annually, and evaluated by the Recovery Team at the end of five years of implementation.