High-Level Inactivity Despite Favorable Environmental Conditions in the Rock-Dwelling Dwarf Tortoise Chersobius boulengeri

Abstract

Abstract In arid regions with summer rainfall, herbivorous reptiles are able to acquire water and fresh food in the presence of high environmental temperatures that can promote ectotherm activity. However, extremely high temperatures and below average rainfall may also limit foraging opportunities due to risks of overheating and predation while gathering scarce food. Karoo Dwarf Tortoises (Chersobius boulengeri) inhabit an arid region in South Africa where most rains fall around austral summer (October–May). We used focal-animal observations and instantaneous recording to assess their behavioral patterns. Despite relatively high rainfall and available plant growth, Karoo Dwarf Tortoises spent approximately 80–90% of their time in retreats. Whereas activity (behavior outside retreats) in the spring was unrelated to time of the day, possibly due to moderate ambient temperatures, activity in the summer was restricted to the afternoon and evening, when tortoises walked and scanned for food and retreats, and fed only 11 min/d on average. In summer, body temperature of tortoises within retreats was positively associated with retreat temperatures, but tortoises appeared to thermoregulate using bodily postures and possibly other means. We suggest that Karoo Dwarf Tortoises mitigate predation risks by maintaining a low level of activity and thermoregulating within retreats. The short feeding time of Karoo Dwarf Tortoises compared to other tortoise taxa may result in slow growth and reproductive rates, which might in turn affect population resilience and conservation needs of this endangered species.