Environmental conditions in burrows of two species of African mole-rat, Georhychus capensis and Cryptomys damarensis

Abstract

Temperature and respiratory gas (CO₂ and O₂) concentrations were measured in the foraging tunnels of burrows naturally inhabited by two species of southern African mole-rats, the Cape mole-rat Georhychus capensis and the Damaraland mole-rat Cryptomys damarensis. Both species are completely fossorial and inhabit closed burrow systems. Tunnels of G. capensis burrows had a mean diameter of 8.7 cm and a depth, measured to the roof of the tunnel, of 6.2 cm; those of C. damarensis had a mean diameter of 6.5 cm and depth of 40 cm. In both species, the mean concentration of CO₂ was higher, and mean concentration of O₂ lower, in burrows than in the surrounding soil or in ambient air. Mean and minimum values of O₂ were 20.4% and 19.8%, respectively, in G. capensis and 20.4% and 19.9% in C. damarensis; mean and maximum values of CO₂ were 0.4% and 1.2% in G. capensis and 0.4% and 6.0% in C. damarensis. Temperature varied between 18.5 and 24.2 °C in burrows of G. capensis by comparison with an ambient range of 16.9 to 26.8 °C; and from 19.6 to 29.3 °C in burrows of C. damarensis by comparison with an ambient range of 8.6 to 30.8 °C. Thus a burrowing habit seems to offer both species protection from extremes of temperature without entailing the cost of a grossly abnormal respiratory environment. From a review of the relevant literature, we conclude that average concentrations of CO₂ and O₂ in mammalian burrows often do not differ greatly from ambient values. However, more work is needed to determine the respiratory gas concentrations in the immediate vicinity of active, burrowing animals.