J. Zool., Lond. (1996) 240, 523-536
Temperature and the tropical tortoise Kinixys spekii:
constraints on activity levelA. HAILEY
Department of Biological Sciences, University of Zimbabwe, PO Box MP167, Mount Pleasant,
Harare, Zimbabwe
AND I. M. COULSON
Sengwa Wildlife Research Institute, Department of National Parks and Wild Life Management,
Private Bag 6002, Gokwe, Zimbabwe
(Accepted 17 October 1995)
(With 5 figures in the text)
Movements of five Kinixys spekii were measured continuously during six weeks of their activity season, by thread-trailing. The mean daily movement distance was negatively correlated with maximum shade air temperature, but not significantly related to minimum temperature, rainfall, or humidity. There was a midday period of inactivity of increasing length as maximum air temperature exceeded 29 oC. Temperatures of models suggest that lower activity on hot days was due to the risk of overheating in this small (mean mass 617 g) tortoise. Kinixys spekii had a mean field body temperature (Tb) of 27 oC, which is low compared to other tortoises (including sympatric Geochelone pardalis, mean Tb = 32.5 oC), but salivated at a similar Tb (38.4oC). This pattern also occurs in other small species; mean and maximum field Tbs of tortoises are positively correlated with body mass, but salivation and critical maximum Tbs do not vary with body mass. Low field Tb provides a wide safety margin before evaporation of water becomes necessary. Kinixys spekii had a short annual activity period, with about 95% of sightings in four months (December to March). Monthly sightings of K. spekii were correlated with rainfall, but not significantly related to temperature or humidity. Seasonal activity is therefore related to rainfall, but within the rainy season the level and pattern of daily activity is related to temperature.