We measured the body mass of 76 (in 2006) and 73 (in 2011) wild ringtailed lemurs (Lemur catta) inhabiting the Berenty Reserve in Madagascar. Compared with the data recorded in 1999 (Koyama et al., 2008), the mean body mass of the adults had decreased significantly. In 2006, the adult females had decreased from 2.27 kg to 1.98 kg, and the adult males from 2.22 kg to 2.03 kg. In 2011, the body mass of both adult males and females was still 1.99 kg. In 2011, the group variations in body mass may have expanded. No sexual difference was observed in body mass, similar to the data from 1999. Despite their reduced body mass, adult females maintained a high birth rate (73.0% annually), but infant mortality was very high (86.2%) from 2006 to 2011. We discuss these phenomena with reference to environmental changes in this reserve
