The influence of rainfall on diet and reproduction in four African rodent species

Arvicanthis nitoticus was found, during two seasons of the study, to begin breeding some two to three months after the start of the rains; at this time weed seeds first appeared in the stomach contents. Breeding continued during the rains and into the early part of the dry season while weed seeds and cereals formed the major part of the diet. Breeding declined during the early part of the dry season, and fat was laid down while weed seeds and cereals were still present but less abundant in the diet. Later in the dry season, breeding ceased and the diet was switched dramatically, first to the leaves and stems of dicotyledonous plants then almost exclusively to grass, and fat deposits were rapidly utilized. Arvicanthis living in an area where cereals were artifically supplied bred almost continuously. Mastomys natalensis also bred when seeds and cereals were most plentiful, but, by ranging widely over open ground, often managed to continue to find these foods, and insects, during the dry season. Supplied cereals failed to produce a reproductive response in Mastomys –instead, unprecedented fat deposits developed. Unseasonal reproduction in this species was, however, observed in an unseasonal wheat crop. Rhabdomys pumilio bred when cereals were plentiful but was also found breeding when its diet was mainly clover–a crop that is noted for its high crude protein content. The herbivorous Otomys angoniensis bred throughout the year and was unaffected by supplied cereals. It seems clear that the food supply of grani‐vorous species is dependent on rainfall, and that prolongation of the normal rainy season may generate excess food and cover, resulting in and extended breeding season and unusually large numbers of these rodents.