Christmas Island National Park

Monday 14 September 2020

skink lazing in the sun on a tree branch Blue-tailed skink

On National Threatened Species Day last year (7 September 2019), 300 blue-tailed skinks (Cryptoblephaurus egeriae), extinct in the wild in their home range of Christmas Island, were released as part of a conservation introduction on the tiny, 2.08 ha island Pulu Blan, part of the Cocos (Keeling) atoll.

This release, designed to augment a successful captive breeding program, has been highly successful with the population on Pulu Blan already increasing through natural recruitment.

Following this success, a second release of 300 skinks was attempted on neighbouring Pulu Blan Madar (1.78 ha) in March 2020.

Aerial shot of Cocos (Keeling) Islands group A second wild release of one of the world’s rarest reptiles has taken place on the island of Pulu Blan Madar in the Cocos (Keeling) Islands group

Three people unloading skinks from a Virgin plane 300 Christmas Island blue-tail skinks from Christmas Island National Park and Taronga Zoo travelled on a Virgin Australia aircraft to their new island paradise before air travel restrictions came into place

However, the skinks released on this island immediately encountered problems. Undetected during a survey of the island in February 2020, a high-density colony of invasive yellow crazy ants (Anoplolepis gracilipes) began impacting the animals, causing scarring to their tails and pushing them to the edges of the island.

A skink’s damaged tail A skink’s damaged tail. Credit: Kristen Schubert

In a bid to save this new release of skinks, Christmas Island National Park staff began looking for ways to remove yellow crazy ants (YCA) from the island.

Yellow crazy ants accessing Vanquish Pro™ from a deployed bait station Yellow crazy ants accessing Vanquish Pro™ from a deployed bait station

A fipronil based paste-like ant bait, Vanquish Pro™ has been found to be highly effective in the control of YCA on Christmas Island. However, its non-target impact on vertebrates such as reptiles is unknown.

Park staff developed a baiting strategy using small sample vials with 4 mm holes drilled in them as bait stations attached to vegetation, to prevent non-target animals accessing the bait. Trials also indicated that reptiles were unaffected by secondary poisoning (eating insects that had consumed Vanquish Pro™).

On the 17 June, park staff deployed over 1000 bait stations containing over 5 kg of Vanquish Pro™ across the island with dramatic effect. In less than 24 hours ant numbers had declined dramatically and are now only present at 17 of 100 monitoring locations on the island.

Further monitoring will establish if the blue-tailed skink population recovers following the baiting. We wish them well!