Résumé
A long-term monitoring program of the Ocellated Lizard (Timon lepidus) population on Oleron Island. - The Ocellated Lizard Timon lepidus (Sauria; Lacertidae) has declined throughout most of its range. Today it is difficult to assess the extent of this decline. The Ocellated Lizard population of Oleron Island (Charente-Maritime, France) is the subject of a long-term monitoring study established in 2007. This study is repeated every 3 years to follow the population evolution. The population is confined to a long-shore dune of 140 ha. The monitoring method consists of 70 plots (50 x 50 m) randomly placed within a study area divided into six distinct zones. Three surveys were conducted in the study area over the spring season (April, May and June). Results were analysed with PRESENCE 3.0 (Beta) and R 2.8.1. The Ocellated Lizard has a highly heterogeneous distribution on Oleron Island. The site-occupancy model allows us to conclude that the probability of detecting the species in the plots increases over the field. In 2010, this probability was 0.78 in April and 0.97 in May and June. The estimated proportion of occupied sites was 0.83 in 2010 and 0.76 in 2007. Colonization and local extinction are the consequences of the evolution of available shelters (colonization if this resource increases and extinction if it disappears) and of the coastal erosion (habitat loss). The relative abundance of Ocellated Lizards on the island (modeling with the N-mixture model) can be principally explained by the presence of permanent shelters (used both during winter and the lizards' active period), including rabbit and rodent burrows and artificial shelters. Rabbits are essential and their maintaining is crucial for the Ocellated Lizard conservation. The Ocellated Lizard population size was estimated to be 1025 individuals (95 % CI: 695-1355) in 2010. This monitoring survey will be replicated in 2013. Results will help us in evaluating and guiding management and conservation measures.