Counting your gecko eggs before they hatch

by Dany Vencatasamy (MWF)

On 12 November 2010, while monitoring one of the 50 Guenthers geckos Phelsuma guentheri that were released on Ile aux Aigrettes earlier in the year (see earlier blog) I came across a pair of Guenther eggs. Had I not been searching for the big fat female gecko, whom we knew was gravid (with eggs), I would not have found the two large white eggs hidden beneath a patch of leaves and glued onto the branch of her favourite Gastonia tree. Guenthers geckos, as most other geckos, only produce two eggs at a time, but unlike most other day geckos the Mauritian species glue their eggs to the substrate. The female first lays two large soft shelled eggs, which she holds with her back legs to dry. As they dry they harden and get stuck to one another and also the rock or branch where the gecko has chosen.

The observation of eggs was very exciting. However, directly after the translocation of geckos in March a female deposited two eggs, which was a surprise as it was out of season, although the eggs were healthy and hatched, to produce two perfectly formed baby geckos. Nevertheless, what we were now witnessing was truly a first, in terms of being the first eggs of the first breeding season, of the first wild group of reproductively active Guenthers geckos outside of Round Island for more than 150 years.
Between September and October many male and female geckos were seen interacting and I managed to observe some pairs displaying courtship behaviour and even mating. By September it was clear that many of the females were gravid, but at this time we were unsure exactly where they would choose to lay their eggs. After finding the first eggs it was clear that other nest sites may also be present and so I started searching around all the known female home ranges, particularly those that I knew were gravid. Over the following four days I managed to find another 17 nest sites, bringing the total number of eggs to 36 eggs. Given the number and location of the eggs that have been located so far we know that at least half of the female geckos we released have laid eggs.

Most of the eggs were found on tree trunks, being different to what is observed on Round Island and whilst they do lay eggs on trunks of Pandanus, eggs are mostly deposited under rock ledges and on the fronds of Latania palms. On Ile aux Aigrettes it appears that the geckos are choosing certain hardwood trees, particularly Eugenia trunks, which they do not usually spend much time on themselves. We think that they are preferentially selecting Eugenia, because the bark is very hard and smooth and therefore a perfect surface to glue eggs onto. This is all very interesting, because on Round Island the geckos do not have these choices and what we are seeing is likely to have occurred in the forests of Mauritius before people arrived and cut them down and introduced mammalian predators that ate all the geckos. Many of the nest sites are at shoulder height so to prevent other fieldworkers on the island knocking them off the trunks as they push through the vegetation in search of Pink Pigeons, Mauritius Fodies and Olive White-eyes we have marked each site by placing an outer perimeter of cord around each vulnerable nesting location.

Since the release of the geckos in March, we have relocated 38 of the 50 individuals, which we can confirm by comparing old scars, tail break marks and particular skin patterns to previous captures and a photographic database, which we are currently working on. However, some of the nest sites have been found in areas where we have never seen individuals, giving us an indication that geckos we have yet to relocate may be present in these areas. I also expect to find more nest sites, particularly as I have only searched for four days and we are have not yet reached the peak of the breeding season. Furthermore, individual females can often lay more than one clutch of eggs within a breeding season. However, I wont be able to search for more eggs until December, as I join the reptile team for monitoring the reptile communities on the northern islands of Gunners Quoin and Round Island.

Currently the eggs look fertile and healthy and we expect that most of them will hatch by Christmas and New Year, but there are many uncertainties, particularly as we are now in the cyclone season.