Homopus signatus signatus is a small tortoise that is endemic to arid northwestern South Africa, where its range is threatened by aridification. It is not clear how the taxon will respond to an aridifying habitat, emphasizing the need for population monitoring. I conducted a mark–recapture study over 5 years with above- and below-average rainfall to analyze population structure, abundance, apparent survival, and effects of rainfall. The population had a continuous size-class distribution and contained similar frequencies of males, females, and juveniles, indicative of a viable population with reproduction and recruitment into adulthood. It consisted of transient and resident individuals, with an abundance of 16–21 resident tortoises/ha. High spring activity levels appeared to result in high (0.35–0.94) recapture rates, which differed among years as a result of different search efforts. Apparent annual survival rates of residents depended on group and increased with shell volume, ranging from 0.74 to 0.99. Although females were the larger sex, their apparent survival tended to be slightly lower than male survival, possibly because of high female activity to accumulate nutrients for the production of large eggs. Rainfall had little effect on apparent survival, suggesting that physiological responses to drought exploited by H. s. signatus are effective in helping them survive. Consequently, mortality during current, periodic droughts does not seem to oppose recommended conservation measures to improve adult survival and delay detrimental effects of aridification on growth and reproduction.
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