Saving reptiles on Christmas Island

Where do you begin?

They call it ‘the Galapagos of the Indian Ocean’, where golden bosun-birds soar over terraced limestone cliffs and the rainforest floor teems with millions of crabs – Christmas Island is truly like nowhere else in the world. But the island’s highly endemic fauna is under pressure. Four species of mammal have gone extinct since human settlement, including the presumed recent loss in 2012 of the endemic pipistrelle bat (see Decision Point #60). And it’s not just the mammals that have suffered. Since 1980, Christmas Island has also witnessed catastrophic declines in reptile numbers, with five of the six native reptiles currently on the verge of extinction.

The Christmas Island giant gecko (pictured above) is the last remaining endemic reptile recorded often in the wild on Christmas Island (and is in decline). It’s believed the forest skink, the vulnerable blind-snake and the native coastal skink, may already be extinct whereas Lister’s gecko and the blue-tailed skink live on only as captive populations. Big challenges lie ahead for managers of the Christmas Island National Park. (Photo by Jason Turl)

The Christmas Island giant gecko (pictured above) is the last remaining endemic reptile recorded often in the wild on Christmas Island (and is in decline). It’s believed the forest skink, the vulnerable blind-snake and the native coastal skink, may already be extinct whereas Lister’s gecko and the blue-tailed skink live on only as captive populations. Big challenges lie ahead for managers of the Christmas Island National Park. (Photo by Jason Turl)

Reptiles under threat 

It is likely that three species, the critically endangered forest skink, (Emoia nativitatis), the vulnerable blind-snake, (Ramphotyphlops exocoeti), and the native coastal skink, (Emoia atrocostata) may already be extinct, however a captive breeding program has been set up for the Lister’s gecko (Lepidodactylus listeri) and blue-tailed skink (Cryptoblepharus egeriae). It’s hoped that these critically-endangered species in this program may avoid extinction through successful reintroductions in the future (Smith et al., 2012). The sixth species, the endangered Christmas Island giant gecko (Cyrtodactylus sadleiri) had declined by 30% by 2008, and although reduced populations remain, it is the last remaining reptile found in the wild.

Taken together, this is believed to be one of the largest reptile decline problems that Australia has ever faced.

By developing a strategic, decision-making framework, this research not only aims to prevent the extinction of five endemic Australian reptile species, but also to develop an adaptive framework to cost-effectively manage and conserve other threatened island fauna.” 

The causes of these reptile declines are unknown, but the accidental introduction of invasive species has had devastating effects on many Christmas Island animals. Park managers on Christmas Island suspect that the reptile declines have resulted from combined pressures from a range of invasive species, including cats, rats and yellow crazy ants. But two other highly invasive species: the Indian wolf snake (Lycodon capucinus) and the giant centipede (Scolopendra subspinipes), have filled the island’s vacant ecological niche of ‘small-reptile predator’ with potentially devastating consequences for the endemic reptiles of Christmas Island which have no experience with such predators (introduced wolf snakes on the Indian Ocean island of Mauritius have had catastrophic impacts on the native reptiles there). However, unlike cats, rats and crazy ants, no control or eradication strategies currently exist for wolf snakes or centipedes, and management actions are yet to be implemented on Christmas Island.

Christmas Island is also sometimes referred to as the ‘kingdom of the crab’ with armies of red crabs playing a major role in shaping the island’s ecosystems. Like many other animals on the island, the red crab is also experiencing worrying declines. (Photo by Jason Turl)

Christmas Island is also sometimes referred to as the ‘kingdom of the crab’ with armies of red crabs playing a major role in shaping the island’s ecosystems. Like many other animals on the island, the red crab is also experiencing worrying declines. (Photo by Jason Turl)

What’s an appropriate response? 

There is no use investing money into conservation action on threatened species without an evidence base (knowledge of the

species ecology, threatening processes and appropriate management strategies) suggesting the investment is likely to pay off. It has almost become accepted that predation is the principal cause of the endemic reptile declines on Christmas Island; but this hypothesis is far from being ‘proved’. The lack of knowledge of key threats limits decision-making and management on the island, which in turn, prevents future reintroductions of the captive populations of Lister’s geckos and blue-tailed skinks, currently breeding successfully both on the island and at Taronga Zoo.

Given catastrophic declines in all the other endemic reptile species on Christmas Island, we need to understand the key threats to the one reptile species that remains in the wild, the giant gecko, and the risk of further decline. This new knowledge is essential for designing management strategies to prevent further declines towards extinction.

My PhD research on Christmas Island aims to identify key threatening processes acting upon the endangered, endemic reptiles and develop ways to effectively target our investment in management to support future reintroductions and mitigate the risk of further decline in the Christmas Island giant gecko. This research strengthens existing links between EDG and Parks Australia (a division of the Australian Government’s Department of the Environment) building on collaborations on Christmas Island and in other Commonwealth national parks. This new project on Christmas Island seeks to achieve a primary management objective outlined by Parks Australia: “Maintain or increase populations of significant native species” (Director of National Parks, 2014).

Melissa Wynn gets up close with a destructive invader: the giant centipede. The centipede preys on small reptiles and is believed to be contributing to the decline of Christmas Island’s native lizards.

Melissa Wynn gets up close with a destructive invader: the giant centipede. The centipede preys on small reptiles and is believed to be contributing to the decline of Christmas Island’s native lizards.

Informed decision making

This collaborative project bridges a critical gap between the research community and governmental departments, and will be one of the first to incorporate both robust decision-making methods and in-situ field experimentation to inform effective and targeted investment management. By developing a strategic, decision-making framework, this research not only aims to prevent the extinction of five endemic Australian reptile species, but also to develop an adaptive framework to cost-effectively manage and conserve other threatened island fauna.

When researching threatened or cryptic species, there is often a lack of empirical data available, and one has to rely on expert knowledge and experience gained in the field in order to make management decisions. Through mathematical models we are able to turn this knowledge into a quantifiable ‘Value-of-Information’ analysis which we can then use to guide decision-making and inform research priorities. Of course, these priorities will depend largely on money, and limited funding in both conservation research and environmental management means that informed decisions must be made carefully within the constraints of budgetary restrictions so that management actions get ‘more bang for their buck’.

Currently I am working with experts from around the country to identify all the potential threats causing reptile declines on Christmas Island and to model the costs, benefits and constraints of all available management actions. These models will form a decision framework, identifying what new information would be of most value to inform research priorities in the field.

This strategic framework allows us to make informed decisions now, about how to effectively manage and conserve the rapidly declining reptiles on Christmas Island, and will provide leverage to guide effective and informed field experimentation within the constraints of limited resources, both on Christmas Island and on other threatened oceanic island communities.

The second component of my PhD will assess the value of information identified in the decision framework, and implement the highest priority research action in the field.

Home away from home: a breeding centre containing captive populations of Lister’s gecko and the blue-tailed skink. These critically-endangered species may not be extinct but there’s little point in releasing them into the wild until we know what is destroying their populations.

Home away from home: a breeding centre containing captive populations of Lister’s gecko and the blue-tailed skink. These critically-endangered species may not be extinct but there’s little point in releasing them into the wild until we know what is destroying their populations.

In the field 

Fieldwork will occur on Christmas Island from September to March in the first two years of the project. We will use a combination of intensive mark-recapture studies (enhanced by VHF tracking and GIS analysis) to simultaneously monitor giant geckos and invasive species. We will be seeking to analyze: species distributions, mortality, demographics, behavioural interactions and temporal / spatial overlap.

We will also examine the gut contents of invasive predators in areas where these species coexist with giant geckos, to determine if predation is occurring (we will do this using a genetic approach available at the South Australian Museum). We hope to then develop effective trapping methods and baits for key predators. We will trial these control strategies to create predator-proof exclosures for future reintroductions of captive bred species.

This research, carried out in partnership with Parks Australia, and hopefully, with future support of international conservation organisations, will incorporate both robust decision-making methods and field experimentation to inform management and support the future reintroduction of critically endangered reptiles into Christmas Island National Park.

The hope is we can make a difference on Christmas Island. However, these efforts may also inform cost-effective management of threatened fauna on other islands around the world.


More info: Melissa Wynn melissa.wynn@anu.edu.au 

References 

Smith MJ, H Cogger, B Tiernan, D Maple, C Boland, F Napier, et al. (2012). An oceanic island reptile community under threat: the decline of reptiles on Christmas Island, Indian Ocean. Herpetological Conservation and Biology, 7, 206-218.

Director of National Parks (2014). Christmas Island National Park Management Plan 2014–2024. Commonwealth of Australia, ISBN: 978-0-9807460-3-7

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