Australia’s endangered species: Christmas Island forest skink

Forrest Gump had been living a spoiled life, locked in a cage on Christmas Island. Until last year, she made two friends, but tragic events killed them all.

Now only Gump remains. She is the last known individual of a forest skink on Earth; a species that was probably already on the brink of extinction, but whose relative longevity has temporarily delayed the final extinction of a species that may have survived for tens or even hundreds of thousands of years.

Her story is instructive. In our lifetime, forest skinks have gone from being abundant across 135 kilometres of rainforest to disappearing.² Christmas Island. The renowned herpetologist Hal Cogger remembers (as recently as 1998) seeing over 80 forest skinks sunning and feeding around a fallen tree; until recent decades they were common and widespread on the island.

Then their numbers began to decline rapidly and seemingly unstoppably. By 2003, they were confined to scattered pockets in remote areas of the island. By 2008, a targeted survey found them in just one locality. Now, recent repeated searches and trapping have failed: the species appears to have disappeared entirely from its natural habitat.

this Emoya The skinks, to which the forest skink belongs, are a large group (over 70 species) that are distinctly distributed across the Pacific Islands. Most skinks (including the forest skink) are medium-sized, stocky, active during the day, and live on the ground. Forest skinks are relatively plain: most have no markings, are chocolate brown, and are about 20 centimeters long (about two-thirds of which is the tail). Recent genetic analysis has concluded that the forest skink is the oldest species in the genus.

status

The rate at which the forest skink is declining and becoming endangered is outpacing its designation as a threatened species. In fact, despite being endangered, it is not yet listed as a threatened species under the Environment Protection and Biodiversity Conservation Act, although it is likely to be added to the threatened species list soon. This speaks not only to the flaws in the official listing process, but also to the speed at which the skink’s population is declining.

Forest skinks share the same plight as most native reptiles on Christmas Island, with numbers declining. Coastal skinks (Brutal Emotions) is nearly extinct on Christmas Island (but is thought to persist elsewhere), and the endemic blue-tailed skink (Cryptochrysopus aegypti) is now probably extinct in the wild (but, more happily than the forest skink, a functional captive breeding population has been established), the endemic Lister’s gecko (Lepidodactylum rex) is nearly extinct in the wild (but a captive breeding population still exists), and the status of the Christmas Island blind snake is unknown (only one individual has been reported in the past two decades). Curiously, another endemic species, the Christmas Island giant gecko (Sasaki’s round-fingered lizardAlthough the disease remains common, it has experienced significant (although as yet unmeasured) declines.

threaten

An interesting but frustrating question in this case is that the cause of the decline remains unresolved. This applies to Christmas Island’s other native reptiles, and perhaps also to the better-known and very similar Christmas Island slugwing.

There are credible suspects, most notably predation by introduced yellow crazy ants, giant centipedes, or wolf snakes; competition with five introduced reptiles; poisoning by pesticides used to control crazy ants; and disease. There is no smoking gun for any of these factors, and it is too late to decipher the clues and control the threat of this species.

But it’s not too late for two other captive, critically endangered Christmas Island lizard species, whose ongoing research may allow us to draw sensible posthumous conclusions about forest skink extinction.

strategy

Sadly, the future of this species is not great. Its sole existing representative is likely to die within the next few years. Efforts to locate more individuals have been ongoing over the past two years, but these efforts have been to no avail. In previous years, there have been several sightings and near misses; these opportunities were tantalizing but failed to materialize. Amid these failures, the survival of this species may have slipped through our fingers.

Perhaps we are too pessimistic. Perhaps there are still some mysterious forest skinks that have not succumbed to the enemies that plague their lives. Optimists may still have time, however limited, to invest in a more comprehensive search to find a mate for the Gump and buy more time to prevent extinction.

A Christmas Island Reptile Species Advisory Group has been established, and captive breeding (on Christmas Island and at Taronga Zoo) is offering hope for two more endangered reptile species.

in conclusion

Failure is a great teacher. This was an extinction event that should never have happened. The lesson is clear:

• The decline can be very rapid and if not responded to quickly, the decline may well lead to extinction.

• Currently, the endangered species listing process is imperfect, but the value of the listing process is limited if it does not provide resources to identify and improve the reasons for listing.

• Early intervention, such as through captive breeding, may provide irreplaceable opportunities for conservation.

• Island biota are extremely vulnerable to extinction and require appropriate biosecurity measures to protect them.

• Identifying the key factors that drive species decline and extinction can be extremely difficult.

From an individual perspective, Forrest Gump is an ordinary, insignificant lizard, but now she has become a talisman, marking the end and approach of extinction. Extinction is a chain, and the last link in the chain is the death of the last individual.

The Conversation is publishing a series of articles on Australia’s endangered species. View here.