Low survival rate and high predation in the African hingeback tortoise Kinixys spekii

Live and dead Kinixys spekii were collected in the Sengwa Wildlife Research Area, Zimbabwe over a 12-year period. Live tortoises were sexable at a midline plastron length of 100 mm; females were considered sexually mature at 140 mm (reached by age 9 years) and males at 120 mm (at age 7 years). Adult females were significantly larger than males, on average by 14 mm in length and by 1.43 times in mass. Mark–recapture analysis in a 2 km2 area showed a population density of sexable tortoises of 0.16 ha−1. The survival rate was estimated by recaptures, by the frequency distribution of age at death, and by the mean age of live tortoises, and averaged 0.74 year−1. Seventy-seven to 89% of dead tortoises showed evidence of predation, depending on the criteria used. Damage occurred in characteristic forms, loss of the front or rear of the plastron, or holes in the carapace and plastron, which were attributed to predation by mammals and ground hornbills, respectively. K. spekii had similar body size and sexual size dimorphism to Mediterranean tortoises (Testudo), but population density was much lower and the mortality rate was twice as high, probably due to the abundant African predators. High mortality was offset by a rate of juvenile growth twice that of Testudo.