Searching for the elusive giant bronze gecko in the Vallée de Mai

Seychelles Islands Foundation, 18/04/11

One of the main reasons for the Vallée de Mai’s World Heritage Status is its high biodiversity and endemism. This is particularly true for its reptiles. The site is home to a remarkable six species of gecko endemic to Seychelles and it may be the only location which hosts all three species of Ailuronyx gecko. This genus is endemic to the Seychelles and likely to be ancient in origin. It is generally considered to contain three species. The most elusive of them, the giant bronze gecko Ailuronyx trachygaster, is known from only a handful of sightings, scraps of anecdotal information and a single museum specimen housed in the Natural History Museum of Paris which was incorrectly assigned to a Madagascan locality until being correctly identified as a Seychelles endemic in 2002. Very little is known about the ecology or evolution of any of the Ailuronyx species and the genus is in need of further research.
SIF has therefore been assisting researchers aiming to shed light on the ecology of and relationship between these species. The Vallée de Mai team has been trying to catch giant geckos for some time and even managed to catch and sample what was thought to be a juvenile giant gecko in 2010. A more recent expedition to the Seychelles by herpetologists from CIBIO at the University of Porto included a visit to the Vallée de Mai where their team was boosted by several enthusiastic SIF staff members. .The aim of the visit was to find, catch and sample DNA from Ailuronyx species and the similarly poorly known and endemic burrowing skinks, with the primary goal being to catch at least one of the adult giant bronzes.

After several hours, the team of researchers and SIF staff had caught a number of burrowing skinks but still no Ailuronyx. One sighting of a giant bronze resulted in a failed capture attempt as the huge gecko evaded grasp and made for the canopy but the team’s enthusiasm was unflagging and persistence ultimately paid off. Finally, with seven people, two ladders, a couple of long poles, and great excitement all round, the team managed to catch, measure and sample an adult giant bronze gecko for possibly the first time on Praslin. The first success was followed by the capture of three more giant bronze individuals over the next 36 hours, resulting in a very respectable sample size of four tail samples for the genetic research as well as important measurements and a closer look at this incredible species. The giant bronze gecko differs from the smaller Ailuronyx species not only by its huge size but also in the proportions of its head and feet which are noticeably broader and larger than those of the medium-sized bronze gecko Ailuronyx seychellensis. It was a privilege to be able to view such a rare reptile close up and the data collected will provide new information on the species which is needed to assess conservation status and management requirements. After all measurements, tail tip collection and much admiration, all of the geckos were released unharmed and scrambled back up their coco de mer trunks.

This collecting trip, during which the CIBIO researchers also collected samples from other islands and locations, should provide an important boost for Ailuronyx research in the Seychelles. All samples will now be analysed by the CIBIO researchers to assess genetic relationships between the different species and islands and the results will be published in due course.

The giant bronze gecko is known to be a rare and ecologically specialised species with a highly localised distribution. It is encouraging that the Vallée de Mai has proved to be an excellent site for these enigmatic animals (as well as the fast-moving burrowing skinks). SIF is aiming to develop research on this species to assess distribution and population size, as well as investigating ecology and threats, to ensure the long-term preservation of this unique Seychelles endemic.

Massive head and feet of the giant bronze gecko Ailuronyx trachygaster (left), gecko on a coco de mer trunk (centre) and SIF Science Programme Officer Wilna Accouche handles a giant gecko (right).

The team in high spirits with the first Ailuronyx trachygaster individual to be captured (L-R): Nathaschia Pierre, Anna Reuleaux, Wilna Accouche, Dr Nancy Bunbury (SIF), Dr James Harris, Dr Sara Rocha and Dr Ana Perera (CIBIO).

Photos by SIF/N. Bunbury 2011.