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Feral Cats: A Menace to the Fauna of Christmas Island

By Phosphate Resources in Environment

What’s the Issue?

Christmas Island was first settled in 1888 and since that date the introduction of flora and fauna has had an enormous impact on the Island. Cats were introduced in 1888 (Tidemann 1994; Algar and Johnston 2010) and well established by 1904 (EWG 2010). They were quickly followed by other invasive species including black rats, yellow crazy ants, and later giant centipedes, giant African land Snails and wolf snakes.

Cats feed on a variety of fauna and have been shown to have deleterious impacts on endemic land vertebrates and breeding bird populations on offshore and oceanic islands around the world (Algar and Johnston 2010). Studies on Christmas Island have confirmed this with research showing that cats target native reptiles, mammals and birds. In one study by van der Lee (1997) analysis of cat stomach contents found that a significant proportion (30-40%) consisted of the native giant gecko, forest skink and blue-tailed skink. Since this study the forest skink has gone extinct, the blue-tailed skink is now only found in captive breeding colonies and the giant gecko has been listed as an Endangered species. Another study by Tidemann (1989) found that cat diet was dominated by three vertebrate species—Christmas Island imperial pigeons, Christmas Island flying-foxes and introduced black rats. The Christmas Island flying-fox numbers have declined significantly and it is now listed as Critically Endangered.  An unpublished study of breeding colonies of red-tailed tropicbirds (a listed migratory species) in the Settlement area found almost complete breeding failure due to cat predation (Ishii 2006).

feral cats figure 1

Figure 1. Cat in nest with Redtailed Tropicbird chick (reproduced from Algar et al 2012)

Clearly cats have had, and continue to have, a major impact on the Christmas Island fauna and are directly implicated in the decline of many species and in some cases extinction. This was highlighted in a Government Expert Working Group Report in 2010 which recommended, as a high priority, that the eradication of feral cats be carried out as soon as possible on Christmas Island to prevent further loss of biodiversity (EWG 2010).

History of cat control on Christmas Island

Since the 1980s, a number of feral cats have been destroyed as part of various studies to determine diet and to test the effectiveness of certain control techniques. However, there had been no concerted effort to control feral cats on Christmas Island. Feral cats were shot opportunistically in the National Park and adjacent areas by park staff. However, this practice was rare and somewhat ad hoc. No formal data was recorded and is unlikely to have had much impact on the cat populations.

In 2003, parties responsible for the management of Christmas Island, in particular Phosphate Resources Limited (PRL), expressed an interest in assessing the feasibility of a program to control feral/stray cats on the island. Joy Wickenden and Mark Bennett (Environmental Adviser and Environmental Manager respectively) approached Dr Dave Algar from WA Department of Parks and Wildlife (formerly the Department of Conservation and Land Management) to provide an initial assessment of the feasibility to control feral/stray cats on Christmas Island (Algar and Brazell 2003). A research program was undertaken the following year to facilitate refinement and validation of the principle control technique to be used in the proposed feral cat eradication program. The program also enabled collection of further information to highlight the need for feral cat control on the island and maintain and foster support and enthusiasm by the local community. This second research program was again initiated and facilitated by Joy and Mark (Algar and Brazell 2005; Algar and Brazell 2008).

In 2008 and 2009, trials of the Curiosity® feral cat bait were also conducted in selected areas on the Island. The trials were part of a collaborative national project between the Commonwealth Department of the Environment, Water, Heritage and the Arts, the Victorian Department of Sustainability and Environment and WA Department of Parks and Wildlife (then Western Australian Department of Environment and Conservation) (Johnston et al. 2010). Logistic support for these trials was provided by Christmas Island National Parks (CINP) and PRL.

In 2010 a management plan for cats and black rats on Christmas Island was developed (Algar and Johnston 2010) which provided a framework for long-term management of cats (and rats) on the Island. The first stage of the plan involved amending the local cat management laws to prohibit the importation of new cats and the requirement to de-sex, microchip and register domestic cats. Drafting the Management Plan was funded by the (then) Attorney Generals Department (later Department of Infrastructure and Regional Development) in 2009/10. The veterinary programs that followed resulted in the registration of 166 domestic cats between October 2010 and May 2012. A survey for domestic cats conducted annually indicated 87 remained in 2015. Within this five-year period 48% of the registered animals were deregistered, either having died from natural causes, were road fatalities, or destroyed as the owners had moved off-island.

The second stage focusses on the removal of all stray (i.e. non-registered) cats in the residential, commercial and light industrial areas of the Island, including the detention centres at North West Point and Phosphate Hill, through trapping and baiting. This ongoing stage of the program prevents repopulation of cleared areas by other feral and stray cats. The success of this stage has been dependent on the completion of the first stage to ensure no identified cats (ie. those with microchips) were euthanized. By the end of 2015, stage 2 has resulted in the trap removal of 349 feral or stray cats and approximately a further 264 cats being poisoned using suspended 1080 baits around the perimeter of the townsite (refer Figure 2). An additional benefit of the baiting program has been the eradication of wild dogs on the island that also found the baits very attractive. The Department of Infrastructure and Regional Development, CINP and SERCO provided financial support for stage 2 of this project. Logistic support was provided by PRL, CINP and the Shire of Christmas Island (SOCI).

feral cats figure 2

Figure 2. Bait suspension device with suspended 1080 cat bait and sand pad to track paw prints (reproduced from Johnson et al 2010)

Whilst the program had successfully focussed on controlling feral cats from the populated areas, cats remained over the majority of the Island. The next step is the implementation of an island-wide baiting program aiming at eradicating all feral cats from the Island. Given the size of the area, dense forest and steep terrain, this represented a major challenge and there was no funding available at this time to resource this program.

Phosphate Resources (PRL) recognised the importance of this program to the recovery of the Island’s biodiversity, and in 2014 committed to providing $1.3 million over five years as an environmental offset project to fund an island-wide cat eradication program. In August 2014 the Director of National Parks committed to match PRL’s contribution to fund the ambitious program. (2015 – $500,000 from Threatened Species Commissioner/2016 – $650 from Director of National Parks)

Benefits and Results

For Christmas Island the benefits of cat removal work supported by a large group of stakeholders including PRL has been observed in and around the residential area in the north-east of the Island. In the year 2005–2006 there was an almost complete failure in the breeding of the red-tailed tropicbird (Ishii 2006). Photographs taken using remote cameras showed both domesticated cats (identifiable by collars) and stray/feral cats predating on red-tailed tropicbird nests and chicks. However, by 2011 there was an observed increase in the nesting success (Algar et al. 2012; Algar et al. 2014). Success rate of the species along the Settlement shoreline which can be linked to the removal of unwanted pet cats and feral/stray cats from the same area. Anecdotal evidence suggested a similar improvement in the nesting success of the white-tailed tropicbird. A recent report by the Commonwealth Threatened Species Commissioner cited a recovery in the breeding success of the Christmas Island flying fox population in 2015 that could be attributed to feral cat management (ABC 2015).

A Team Effort

Eradicating an invasive species is a difficult and often impossible task. Whilst islands are ‘contained’, an island the size of Christmas Island (135 km2) is a massive challenge, made all the harder by dense forest, steep terrain and limited access to many areas. With multiple land tenures and human settlements the success of this program relies on multiple partners, significant funding and a common purpose. On Christmas Island the cat eradication program is a community effort with CINP, SOCI, PRL and the Australian Border Force all key partners in the program.

To ensure ongoing support from the local community the program has been designed with a focus on education and communication. This has ensured the Island population has been supportive with an optimistic and constructive view of the work.

PRL are proud to have been a strong supporter and partner is this program since 2003. The company is strongly committed to assisting in the fight against invasive species on the Island and sees this as the most positive way to address biodiversity decline on the Island.

References

Algar, D., Hamilton, N., Holdsworth, M. and Robinson, S. 2012. Eradicating Christmas Island of cats and black rats. LANDSCOPE 27(4), 43–47.

Algar, D., Hamilton, N. and Pink, C. 2014. Progress in eradicating cats (Felis catus) on Christmas Island to conserve biodiversity.  Raffles Bulletin of Zoology Supplement No 30, 45–53.

Algar, D., and Johnston, M. 2010. Proposed Management plan for cats and black rats on Christmas Island, Western Australian Department of Environment and Conservation.

Australian Broadcasting Corporation 2015. At http://www.abc.net.au/news/2015-12-04/scientists-scramble-to-save-christmas-island-flying-fox/7003238 visited 23 November 2016.

Expert Working Group 2010. Final Report of the Christmas Island Expert Working Group to the Minister for Environment Protection, Heritage and the Arts ed Department of Sustainability Environment, Water, Population and Communities.

Ishii, N. 2006. A survey of Red-tailed Tropicbird Phaethon rubricauda at the Sitting Room and Rumah Tinggi, Christmas Island, April–July, 2006. Unpublished Report to Parks Australia, Christmas Island Biodiversity Monitoring Program.

Johnston, M., Algar, D., Hamilton, N. and Lindeman, M. (2010). A bait efficacy trial for the management of feral cats on Christmas Island. Arthur Rylah Institute for Environmental Research Technical Report Series No. 200. Department of Sustainability and Environment, Heidelberg, Victoria.

Lee, van der, G. 1997. The status of cats Felis catus and prospects for their control on Christmas Island. A Consultancy for the Australian Nature Conservation Agency. Department of Ecosystem Management, University of New England.

Johnston, M., Algar, D., Hamilton, N. and Lindeman, M. 2010. A bait efficacy trial for the management of feral cats on Christmas Island. Arthur Rylah Institute for Environmental Research Technical Report Series No. 200 Department of Sustainability and Environment, Heidelberg, Victoria.

Tidemann, C.R. 1989. Survey of the terrestrial mammals on Christmas Island (Indian Ocean). Australian National University, Canberra. Unpublished report to Australian National Parks and Wildlife Service, Canberra.

Tidemann, C. R., Yorkston, H. D. and Russack, A. J. 1994. The diet of cats, Felis catus, on Christmas Island, Indian Ocean. Wildlife Research 21, 279–286.