Population fluctuations, reproduction and survival in the Striped fieldmouse <i>Rhabdomys pumilio</i> on the Cape Flats, South Africa

Abstract

A wild population of Striped fieldmice was studied for a continuous period of five years in an area of alien Acacio bush about 24 km from Cape Town, South Africa. Mice were live‐trapped, marked by toe‐clipping and released on a 60‐station grid, and also kill‐trapped in a separate area. Marked annual fluctuations in the population size were correlated with a 6–8 month summer breeding season. There were also marked inter‐annual differences in peak population size. The age of sexual maturity of females was determined from the first pregnancy which occurred at 6–7 weeks old; and of males from the presence of visible spermatozoa in the vas deferens which occurred at about 11 weeks old. Litter size was affected by both the age and the body mass of the female. It appeared that mean survival from birth was only approximately 1.5 months and that survival from first capture was about 1.9–2.5 months. This high mortality appeared to be the major reason for the sharp seasonal fluctuations in population size and may also have been responsible for the interannual differences since marked changes in survival were recorded between some years.