The configuration and dynamics of six Bathyergus suillus and one Cryptomys hottentotus burrow systems in coastal fynbos vegetation was studied for a year by monitoring mound production and excavating burrows. Bathyergus suillus is a large solitary mole-rat and C. hottentotus is smaller and social. Our results are compared with those for other subterranean rodents.
Most B. suillus burrows (15–22 cm in diameter) were 40–65 cm below ground to prevent their collapse in the seasonally softer and drier surface sand; the burrows were consequently situated deeper than most food plants. Cryptomus hottentotus burrows were narrower (5–7 cm) and shallower (<35 cm), facilitating food location but restricting these mole-rats to more consolidated soils. Bathyergus suillus and C. hottentotus burrows were of similar length (up to 400 m) but in terms of biomass per metre, C. hottentotus and other small social mole-rats have relatively longer systems. The mean home range of B. suillus (0.27 ha) was higher than most subterranean rodents, including C. hottentotus (0.16 ha), but their mean density (0.9 ha−1) and biomass (≏ 500 g ha−1) was low. Bathyergus suillus appear to remain resident in an area and to have an optimum burrow length, maintained by blocking old burrows with newly-excavated soil. This blocking may promote rapid regeneration of food plants within the home range. Daily burrow extension (estimated from mound production alone) averaged 0.7 m for both mole-rats. The maximum monthly burrow extension was 141 m for B. suillus and 47 m for C. hottentotus. All mole-rats have a characteristically clumped and patchy distribution, reasons for this are discussed.
Bathyergus suillus cats and uses as nesting a wide range of roots, leaves and stems but preferentially selects some plant species. It rarely stores food. Cryptomys hottentotus eats and stores geophytes. Reasons for these dietary differences and the possibility that mole-rats act as agents of dispersal of geophytes are discussed.