This study examines aspects of the nesting behaviour of Brants' whistling rat Parotomys brantsii, a medium-sized rodent indigenous to southern Africa. In the semi-arid regions in which it occurs P. brantsii breeds opportunistically, modifying its breeding period in relation to rainfall. Within a winter rainfall area, females produced up to four litters of three to four young during the winter–spring period following a gestation period of c. 38 days, with females showing a post-partum oestrus. The behaviour of females was modified by the birth of their pups, after which they spent extended periods underground, interspersed with bouts of food-collecting activity. With the emergence of pups above-ground, females increased their vigilant activity. At 5 weeks pups had developed all the important behavioural characteristics of adults, such as creating their own overnight food stores, collecting nesting material and defending a warren area against conspecifics. This was also the age at which the young dispersed from their natal nest area as well as the time at which females could reach sexual maturity, despite physical immaturity. The high reproductive output of female P. brantsii, as well as the rapid ontogeny of their young, compared to other otomyine rodent species, may represent an adaptation for maximizing reproductive potential in the semi-arid areas they inhabit.