Overcoming low environmental temperatures in the primary feeding season: low-level activity and long basking in the tortoise Homopus signatus

Abstract

Tortoises that live in regions where food plants grow in winter may have to cope with relatively low environmental temperatures to obtain resources. The speckled tortoise, Homopus signatus, inhabits an arid winter rainfall range where it is active in winter and spring at environmental temperatures well below its preferred body temperature. Although H. signatus is a threatened species, we have no information how it deals with low environmental temperatures. Therefore, we made continuous recordings of behaviour in nine female H. signatus on 29 days in the early spring. The group of females as a whole showed activity (i.e., behaviours other than hiding) throughout the day in a unimodal pattern. However, individual tortoises were active only for approximately 4.5 h per day and spent as much as 73% of their active time basking, mostly under the protective cover of shrubs. In addition, a negative relationship between the percentage of active time spent in sun and environmental temperature indicated that H. signatus used active behaviours other than basking to absorb heat, particularly on cold days. Tortoises completed all active behaviours other than basking in 1.2 h per day, including a mere 24 min of feeding, probably facilitated by the abundant availability of food plants in the early spring. We predict that a reduced availability of food plants for H. signatus might lead to increased active time and possibly increased predation pressure, or to a decreased proportion of active time spent basking and reduced body temperatures.