The population of the Near Threatened brown lemur Eulemur fulvus on the island of Mayotte was censused in 1974, 1984 and 1999. We carried out a new census in 2008, estimating individual and group densities in the three main habitat types on the island (preserved forest, anthropogenic forest and agricultural areas), and more generally evaluating population trends. Data included sex ratios and the number of young < 1 year-old per female. The census was at the end of the dry season, along 14 transect lines of 0.5 or 1 km length. Counts of groups and individuals were repeated three times between 07.00 and 10.00 and between 15.00 and 18.00. The densities of groups and individuals were calculated using Distance. By 2008 group and individual densities had significantly decreased in preserved forest, and there was also a decrease in group size in all habitat types. The 2008 census also showed that the overall population of E. fulvus on Mayotte has decreased by about half since 1999. We suggest that these changes reflect environmental stress associated with a decrease in available food resources. Urgent action to preserve forest habitat is necessary for the long-term survival of this lemur.

The population of the Mayotte brown lemur Eulemur fulvus fulvus on the island of Mayotte in the Indian Ocean was reported to have decreased by 50% between 1975 and 1987, from 50,000 to 25,000. From a series of censuses carried out in 1999 and 2000 in the various vegetation types of the island, we estimate that the lemur population now numbers 42,000–72,000. The decline observed in 1987 may have been largely caused by the cyclone that devastated Mayotte in 1984. That the population has recovered must not obscure the fact that loss of forest, increased human pressure associated with further development of infrastructure, and changes in agricultural practices will undoubtedly continue to affect this species on Mayotte.