Tortoise ecology in the West African savannah: multi-scale habitat selection and activity patterns of a threatened giant species, and its ecological relationships with a smaller-sized species

The status of most vertebrates in the African Sahel is not well known. Among these, the African spurred tortoise (Centrochelys sulcata), a charismatic but also one of most threatened vertebrates in the Sahel, is still poorly studied. We investigated the status of this species, its potential distribution, habitat selection (at multiple spatial scales) and activity patterns in Mali and Burkina Faso, two countries within the tortoise’ known range. We employed field surveys and villager interviews in 23 sites to determine the presence of the species. In these surveys and interviews, we also included the Western hinge-back tortoise (Kinixys nogueyi), a sympatric chelonian also suspected of being in decline. Age-stratified interviews revealed that C. sulcata is widespread in Mali, but since there was a statistically higher frequency of older respondents that remembered C. sulcata present around their village, compared to younger respondents, it is likely that the species has been declining throughout the study area. We encountered a total 77 C. sulcata and 20 K. nogueyi individuals during our field surveys. Most C. sulcata were found along areas of intermittent streams and stabilised dunes, known locally as koris. Centrochelys sulcata individuals were more likely to occur in sandy dry savannah areas that were further away from human settlements, and which contained inland waters or were closer to these. Kinixys nogueyi exhibited instead an allopatric distribution, with no ascertained sympatry with C. sulcata at the microhabitat scale. Cattle incidence was negatively correlated with the presence by C. sulcata. Our results also indicate that aboveground activity of C. sulcata is limited to the wet season and has a clearly bimodal diel activity cycle, with most sightings in the early morning hours. We provide suggestions on how best to survey this species in the wild while advancing new information on its distribution and biology. These data are invaluable to assess the stat