Micromammalian distribution and abundance in the Western Cape Province, south Africa, as evidenced by Barn owls Tyto alba (Scopoli)

The history of Western Cape mammalogy began almost 200 years ago with Thunberg ( 1811) and has been augmented periodically ever since. The present paper follows Vernon ( 1972) and Grindley et al. ( 1973) in eliciting information from material in Barn owl Tyto alba (Scopoli) pellets. Analyses are based on identified and counted mandibles and maxillae. The Laminate vlei rat, Otomys laminatus Thomas and Schwann, and Krebs's fat mouse, Steatomys krebsii Peters, are shown to have wider distributions than were previously recorded. The Southern multimammate mouse, Mastomys coucha ( A. Smith), is apparently expanding its range westwards, a move probably enabled by changes in vegetation due to farming practices. There appears to be some correspondence between proportional representation of some species and rainfall, either its amount per annum or its seasonality. Variation in alveolar length in Cape gerbils, Tatera afra ( Gray), taken as a proxy for mean individual mass, suggests that mean size in this species may be influenced by rainfall seasonality. Although the Vlei rat, Otomys irroratus (Brants), is known to breed throughout the year, the present evidence indicates that in the West Coast National Park births peak in late spring and early summer, some two months after maximum rainfall. The Western Cape data support the concept that T. alba is a selective opportunist. Sample structure and co-occurrence of species in individual pellets both show that in some cases the owls are more nearly opportunistic while in others they appear to be considerably more selective.