Foraging in wild and captive colonies of the common mole-rat Cryptomys hottentotus hottentotus (Rodentia : Bathyergidae)

The foraging behaviour of wild and captive colonies of the common mole-rat Cryptomys hottentotus hottentotus was investigated. Field studies were unde rtaken at Steinkopf, an arid site in the Northern Cape, South Africa. The r esource biomass and the total available energy here were amongst the highes t recorded for any bathyergids, but geophytes were sparse and widely distri buted. The low probability of locating these widely dispersed resources sho uld promote co-operative foraging in these mole-rats. All common geophyte s pecies were consumed, probably because high burrowing costs favour dietary generalism. The mole-rat biomass per metre of burrow system (0.5-1.5 g.m(-1 )) remains the lowest of any subterranean mammal. Burrow depths and diamete rs were positively correlated to the average mass of the mole-rats in each colony, apparently minimizing energetic costs and maximizing foraging succe ss. Bulbs were stored in central food caches, and both field and laboratory data indicated size-based selectivity in their storage and consumption. As predicted by central place foraging theory, large bulbs were preferentiall y stored, and small bulbs preferentially consumed. However, factors other t han energetic considerations may also influence these storage decisions. To tal consumption time of bulbs was negatively correlated to animal size, and furthermore smaller bulbs were consumed more rapidly than larger ones. In addition to geophyte-storing, C. h. hottentotus also exhibited an alternati ve foraging strategy, termed 'geophyte farming', in which large bulbs were left and eaten in situ, and served as a renewable resource. Together with t hese foraging specializations, the evolution of sociality in mole-rats is a key factor which enables them to live in some of the most formidable habit ats in Africa.