The Pink House Re-introduction of the Christmas Island Blue-tailed Skink

The Christmas island Blue-tailed Skink (Cryptoblepharus egerniae) is a small skink endemic to Christmas Island in the Indian Ocean. In the past the skink was common in large numbers in the settled areas and had also been observed in rainforest clearings elsewhere on the island.

In 2010, after witnessing a dramatic decline in numbers, the last Blue-tailed Skinks were captured from the wild for captive breeding. The lizard has not been sighted in the wild since that time.

Less than 70 individuals were captured and held in both specially constructed tanks and netted outdoor enclosures at The Pink House research station. Part of the group was moved to another facility on the Australian mainland as an insurance population.

In the last seven years the population of skinks has increased in number to around 1300 today. Last week around 140 skinks were released into a new much larger, soft-release enclosure where the lizards will be left to fend for themselves. The enclosure has been prepared over many months, and any of the introduced ants, snakes and centipedes that are believed to have contributed to the decline of the species have been removed. However, the enclosure is not netted so the lizards will still be at risk of predation from the Christmas Island Goshawk and Christmas Island Hawk-owl.

The lizards will be monitored intensively to document their behaviour and survivability. Half the lizards were marked with coloured nail polish to identify individuals from a distance.

Obviously, reintroducing the lizards to various parts of the island is the ultimate goal but that's a fair way off yet. This is the next step toward that end.


One side of the large enclosure.


Inside the enclosure. The small fences you see are pit-trap fences used to remove the introduced predators, and may be used again if the lizards need to be caught. But at this point the pits are covered and the lizards can go around the fences.








Hix

 

Great info Hix! Where on the mainland were the insurance population of skinks sent? Is there any chance of some of these going on display to the public anytime?

 

Wouldn't marking them with nail polish put them at greater risk of being eaten by a raptor?

 

Without a doubt in these circumstances captive-breeding and ex situ conservation are important tools to ensure in situ survival of local endemics or vulnerable species.

What needs to be done next - and that is a huge challenge - to rid Christmas Island full stop of all exotics detrimental to the Island ecosystem and endemic flora and fauna.

 

Taronga has built up their numbers so may put them on display at some point. I'd rather they sent some of their stock to other zoos too - Perth would be an obvious choice considering all the conservation work they have been doing recently.

@Coelacanth18 : there are three raptors on the island. The Hawk-owl is not likely to be a problem as the lizards are diurnal. The Nankeen Kestrels are only in the settled part of the island 15 kms away. However the CI Goshawk is a potential risk. The authorities are expecting some losses anyway, and this would be a quick way to be able to monitor those losses (whether they be from goshawk predation or other factors).

@Kifaru Bwana: unfortunately, due to the nature and size of the island, eradicating the yellow crazy ants, centipedes and rats is not believed possible. Investigations are starting on the Wolf Snake to gather data. At this stage it is only the feral cats that are thought to be able to be eliminated, but that may not happen for another ten years.



Hix

 

Has anybody figured out why the skink population crashed rapidly and all across its range on the island where it had been in large numbers?

 

It is believed to have been all the introductions, particularly the Yellow Crazy Ant. But nobody knows for certain. And a new disease has appeared that might also have been a factor.

Interestingly, the Giant Gecko seems to still be in good numbers in the wild and research is being conducted to try and determine why this is.



Hix

 

The geckos are nocturnal, right? Maybe this has allowed them to avoid the introduced threats to a greater degree than the other lizard species on the island.

 

A logical thought, but then Lister's Gecko is extinct in the wild too.



Hix

 

Surely they need to eradicate Yellow-crazy ants (or to at least make an attempt to cut down numbers) as they are impacting many of the native species.

 

The Yellow Crazy Ants were accidentally introduced back in the 1990s and have since taken over large parts of the island. As well as the reptiles, they may also be responsible for the extinction of the Christmas Island Pipistrelle whose numbers plummeted in the early 00's and was declared extinct in 2009.

Because of the terrain and the inaccessibility of many areas it is not thought possible to eradicate the ants. One of the issues has been the formation of super-colonies which require management (usually with Fipronil and other ant baits). One of the things that supports the ant colonies is a small scale insect, the Lac Scale, also introduced, which produces a sugary secretion that the ants feed upon. Several years ago one of the National Parks researchers went to Malaysia and identified a small parasitic wasp species that parasitizes the Lac Scale, and after a lot of negotiation and red tape a few of hundred of the wasps were imported to Christmas Island late last year.

The wasps were placed in a greenhouse to breed them up, the process expected to take six to nine months before there were enough for release. The wasps, however, had other ideas. The liked the climate here so much they didn't just thrive, their population exploded and the first release happened only six weeks after the initial importation.

It is believed that when the wasp numbers get high enough the Scale Insect numbers will crash, before a balance eventually is reached. The reduction in a high sugar food content for the ants will result in a reduction in ant numbers. However, it is not thought that the ants will be eliminated, but at least there should be no more super-colonies.



Hix

 

How has this solution worked so far?

 

The wasps have bred in the wild and are slowly expanding their range, at about 300 metres per year (remember the wasp is only about 1-2mm long). There hasn't been any significant change in the ant numbers....yet.

The National Park is now breeding up more wasps for release in other areas and have even put out an "Adopt-a-Wasp" poster for the general public: if you find scale on the trees in your garden or near your house, parks will give you a card full of wasp-infested scales for you to hang in your garden.

The National Park expects we should have something to report by the end of the year.



Hix

 

Supposedly this species was seen again this year.

 

Really? I didn't hear about that.

 

I have seen skinks listed as being the Christmas Island species for sale at US herp expos a couple of times in the past. Is there an internationally trade in these animals or is something fishy going on?

~Thylo

 

Maybe from Christmas Island in the Pacific?



Hix

 

Are those in the pet trade either? I remember the animals I saw having blue tales but could be wrong.

~Thylo

 

Emoia cyanura are found in Kiribati (of which Christmas Island is a part). There's more chance of them being in the trade than the Indian Ocean Christmas Island skinks.