Telfair’s skinks and Guenther’s geckos released on Ile aux Aigrettes

By Nik Cole, Durrell Mauritius Programme

March 2010 has been a busy month for the staff of the reptile team in Mauritius, translocating 550 endangered reptiles from Round Island to the nature reserve island Ile aux Aigrettes. This translocation forms part of our ongoing work to rebuild the lost endemic reptile communities of Mauritius with the Mauritian Wildlife Foundation and the National Parks and Conservation Service.

If you have seen some of the earlier blogs on Mauritius you‘ll know that Ile aux Aigrettes is an important site for the restoration and preservation of one of the last remnants of dry Mauritian coastal forest. Over the past 20 years nearly all invasive plants and numerous exotic animals, such as cats and rats have been removed. The restoration process has led to the re-introduction of endangered plant and animal species. Last year rats were again detected on the island and after a really intensive effort, it seems that we have been able to eradicate them. This opens the way to bring more Telfair’s skinks and Guenther’s geckos back onto the island.

The Telfair’s skinks and Guenther’s geckos are the largest of the Mauritian lizards. The skink can attain a total length of over 40cm and the gecko over 30cm. At over 30cm it places the Guenther’s gecko amongst some of the largest geckos that are still alive on the planet.

Fifty Guenther’s geckos were captured throughout the palm rich areas of Round Island where the population in this habitat has been estimated at approximately 4,000 individuals. Capturing the geckos required a team effort, as they are quick to avoid capture and can inflict a vicious bite, but more importantly incorrect capture or handling can cause damage to the gecko’s skin or tail. No geckos were injured during the round up, although the occasional bite was inflicted to the captor! Captures were made on the day and evening prior to their transportation to Ile aux Aigrettes to limit the time they were held in individual cloth bags. Each gecko was weighed and measured and distinguishing marks were recorded to aid in post release recognition.

The translocation of geckos occurred in three phases with the release of 15 geckos on the 18th, 21 geckos on the 22nd and 14 geckos on 26th March. For each release the geckos were loaded into secure containers and flown by the Police Helicopter Squadron 62km to the southeast coast of Mauritius. They were then transported onto an awaiting boat, which took them on the 600m journey across the lagoon to Ile aux Aigrettes. The entire journey from Round Island to Ile aux Aigrettes took less than an hour. The geckos were then released at pre-selected positions within the mature coastal forest in a particular order to maintain a similar social structure found within the palm rich areas on Round Island. The release area also encompasses derelict buildings, which the geckos are likely to use as egg laying sites. Already, a female gecko that was released on 22nd March has deposited two eggs in a currently unused Pink Pigeon aviary.

The geckos were not the only reptilian passengers on the helicopter trips. During the two days prior to each helicopter trip, we spent the mornings capturing skinks from all locations across the island. Again we were very selective with what we caught and chose only fit and healthy individuals. We selected 500 skinks from the 20-30,000 individuals on the island, which consisted of 175 males, 225 females and 100 sub-adults of unknown sex. Each skink was measured and weighed and PIT tagged. A PIT (Passive Integrated Transponder) tag is inserted just beneath the skin and emits a unique number when read with an electronic reading device; this allows us to identify every individual. Unlike the geckos, the skinks have a very thick skin, which allows the tags to be inserted without any problems.

Each skink was held in an individual cloth bag prior to release, but where they were held in bags for a slightly longer time than the geckos, we offered them food and water. The most popular item on the Round Island menu for the skinks is cockroach, which we caught for them at night. Despite the awful cockroach smell, there were no complaints from the skinks, which happily ate them in their bags. The skinks were then transported in separate containers to the geckos, and released by teams of three to four people on Ile aux Aigrettes. Each team released the skinks in pairs of male and female or sub-adult and male/female at 25m intervals across an existing grid system throughout the forest on the island.

When we first released Telfair’s skinks on Ile aux Aigrettes in 2006/07 it caused substantial declines in the certain populations of invasive species, such as the introduced musk shrew. However, we suspect that shrews, which cannot be eradicated from the island using the techniques that we have used to remove the rats, are eating the eggs of the skinks and preventing the skink population from growing. The release of additional skinks onto Ile aux Aigrettes has raised the population above 600 individuals. We predict that this number of skinks will cause a severe decline and possibly the eradication of the shrew from the island and allow the skink’s eggs to survive and the population to grow.