- In the 1990s most of Christmas Island’s lizard species began plummeting. The cause remains a mystery.
- Scientists began a captive breeding program in 2009 – saving two species – but one species had already gone extinct and another is extirpated from the island, but can still be found elsewhere.
- Researchers will not be able to reintroduce the captive species until the cause of the decline is uncovered.
Islands possess many unique gifts from evolution. Their isolation from the mainland give them an identity all their own: these small pieces of land are often filled with species that cannot be found anywhere else on the planet. Christmas Island is no exception. Situated in the Indian Ocean, this Australian External Territory is 360 kilometers south of Java and 1400 kilometers northwest of Australia. Roughly the size of San Francisco, Christmas Island comes in at only 135 square kilometers. But, many species are found here – and nowhere else.
Until recently, this was especially true of lizards. Up until the 1970s, five native lizard species – four of which were endemic (i.e. found nowhere else) – abundantly roamed across the tropical island. But then – after withstanding 100 years of human settlement – four of these lizards rapidly declined. And as of right now, none of these four species can be found in the wild. Two are presumed extinct.
Fortunately, in August 2009, park officials collected as many lizards as possible in order to initiate a captive breeding program. Now, Dr. John Woinarski at Charles Darwin University in Australia and his team at Parks Australia are maintaining and monitoring the breeding program. With the hopes of bringing some of these populations back to life—in the wild.
But, why did the lizards disappear in the first place? And will these unique gifts ever be seen in the wild again?
A rare find
Named on Christmas Day in 1643, the island was not officially settled until the 1880s after surveyors on the HMS Egeria discovered that many of the rocks were pure phosphate. This would change the island’s destiny.
Naturalist J.J. Lister was on this excursion. But, he had a different perspective of Christmas Island. After ten days walking through the dense brush, he declared in 1888 that the island’s “most striking feature is the peculiarity of the fauna.”
Soon after, phosphate mining – not peculiar fauna – lured settlers to Christmas Island. And since the 120 years of human settlement, approximately 25 percent of the native forest habitats were lost. However, the remaining area is now a national park.
Another unusual feature of the island is that C.W. Andrews with the British Museum created a thorough biodiversity inventory in 1897. It is rare to have a comprehensive record created near the start of human habitation.
For conservationists like Woinarski, the inventory is “a remarkable basis to assess the changes associated with human arrival and land use.”
Over the past 120 years, reptile populations were evaluated intermittently. In the 1990s, a team of ecologists realized something had changed – populations were declining drastically.
Biodiversity 911
During this time, the blue-tailed skink (<i), the Christmas Island forest skink (Emoia nativitatis), Lister’s gecko (Lepidodactylus listeri), and the non-endemic coastal skink (Emoia atrocostataCyrtodactylus sadleiri) remains widespread across the island.
Researchers do not know why the four lizard populations dropped precipitously, but it appears there could be multiple culprits. Many non-native predators of these lizards were introduced to Christmas Island after humans first stepped foot on the shoreline, including feral cats (Felis catus), giant centipedes (Scolopendra subspinipes), and wolf snakes (Lycodon capucinus).
The introduction of the yellow crazy ant (Anoplolepsis gracilipes) caused what researchers call an “invasional meltdown”. Yellow crazy ants changed the native vegetation, and the diversity and abundance of food for the lizards.
Parks Australia initiated an emergency response in August 2009. Parks Australia manages national parks in Australia’s external territories, while states and territories are in charge of mainland conservation.
From August 2009, scientists collected every lizard they could find. This included: 64 blue-tailed skinks, 43 Lister’s geckos, and 3 forest skinks. No coastal skinks were collected, and although they are no longer found on Christmas Island they survive on other islands.
Unfortunately, all three forest skinks collected were females, and the last one died in captivity in 2014. The species is presumed extinct.
State of the skinks
Although this response came too late for the forest and coastal skinks on Christmas Island, it is rejuvenating the populations of the blue-tailed skinks and Lister’s geckos.
“The captive population… continues to increase,” Woinarski said. “The populations of blue-tailed skinks have recently passed 1,000 individuals, and there are now over 900 Lister’s geckos.”
Officials not only established facilities on Christmas Island, but lizards were also transported to the Taronga Zoo in Sydney as insurance populations. The captive populations are stable.
The captive breeding program is a means to an end – the ultimate goal is to get surviving species back into the wild. But, this will take time.
Scientists won’t rewild the lizards until they are able to identify the main threats. The isolation of Christmas Island also poses problems. Many conservation programs release fauna on nearby islands where the main threat is absent. In this case, there are no satellite islands.
Currently, the team is performing small-scale re-introductions with blue-tailed skinks, and excluding different sets of invasive predators. Looking at different combinations of threats should help researchers pinpoint what was the most critical driver of the lizard decline. They are also figuring out practical methods to control predators.
Woinarski believes the biggest driver was most likely the wolf snake. Not only was it introduced shortly after the lizards started to decline, but it is a specialized lizard eater. In addition, after it was introduced, it spread rapidly in a pattern that was very similar to the lizards’ decline.
Islands present a conservation challenge for scientists. They contain peculiarities that cannot be found anywhere else on the planet. These isolated pieces of land “provide much that is weird and wonderful in the world’s biodiversity,” Woinarski said. But, biodiversity declines—and extinction—can happen quickly.
The lizards on Christmas Island are a clear example. Nevertheless, Christmas Island is also an example of researchers and the government working together to create a hopeful conservation story.
Citations:
Andrew, P., Cogger, H., Driscoll, D., Flakus, S., Harlow, P., Maple, D., Misso, M., Pink,
C., Retallick, K., Rose, K., Tiernan, B., West, J., Woinarski, J. C. (2016).
Somewhat saved: a captive breeding programme for two endemic Christmas
Island lizard species, now extinct in the wild. Oryx, 1-4.
Lister, J.J. (1888). On the natural history of Christmas Island in the Indian Ocean.
Proceedings of the Zoological Society of London, 512-531.