Short term monitoring reveals the rapid decline of southern Madagascar's Critically Endangered tortoise species

Southern Madagascar supports two of the world's most threatened chelonians, Pyxis arachnoides and Astrochelys radiata, both thought to be rapidly declining as a result of habitat loss and poaching; however, to date quantitative data on this decline is lacking. We applied a conventional distance sampling procedure, monitoring populations twice over a 24-month period across the species' respective distributions. Population density for P. arachnoides dropped from 2.4 tortoises/ha (95% CI; 1.6–3.4) to 1.5/ha (95% CI; 0.8–2.8). Astrochelys radiata dropped from 2.1 tortoises/ha (95% CI 1.2–3.5) to 1.5/h. (95% CI 0.7–3.3). Local community-based conservation initiatives need to be expanded to combat this decline.