Reproductive ecology and egg production of the radiated tortoise (Geochelone radiata) in southern Madagascar

Abstract

We studied reproduction of wild Geochelone radiata at the Cap Sainte Marie Special Reserve in southwestern Madagascar to gain insight into life history traits related to reproductive success. Reproductive behaviour was observed over two nesting seasons and egg production was studied by radiographing telemetered females at regular intervals. We captured and marked 1438 radiated tortoises of which 26% were adults. Mating and nesting coincided with the rainy season, and mating events peaked in December, shortly before females started nesting in January. The incubation period was approximately 263–342 days, and hatchlings emerged after the onset of the rainy season when new plant growth became available. Hatching success was high and incidental destruction by humans rather than predation had the greatest impact on tortoise nests. Individual females produced from 0–3 clutches per season with 1–5 eggs per clutch. Body size had a weak effect on clutch size, but clutch size was lower in the dry year (2000) than in the wet year (1999) and appears to reflect resource availability. Mean egg size per clutch increased significantly with increasing body size. These findings emphasize that protection of large females should be considered in the conservation of this species.