Dynamics in the sand lizard (Lacerta agilis) population at Forteiland, IJmuiden, The Netherlands

In 2000, an isolated population of sand lizards (Lacerta agilis) was discovered on an island in the Netherlands. The population-size was estimated at 57 adult individuals. Subsequently, the area has been improved to make the habitat more suitable for sand lizards. After 5 years of monitoring the population-size was estimated again. There are no indications for major population-size changes, for the population-size is estimated at 59 adult individuals. There is no signifi cant difference in the population structure, although males were more abundant in 2005 than in 2001. Males outnumbered females in both years. The newly made dunes are populated by males, females and sub-adults. Gulls do not seem to conduct a predator stress, as there were no lizards seen there with autotomy. Nevertheless, gulls are believed to negatively infl uence habitat quality for the lizards. On the short term, cats seem to be the biggest threat to the sand lizards as there are strong indications that they have killed 10 % of the whole population within six weeks.