Assessing the threat of avian predation on a small viperid snake

Abstract

Predators are important because they influence survival rates, population density and behaviour of prey species. However, assessing the predation pressure facing a particular species is difficult when that species faces a suite of predators. We aimed to characterize the suite of avian predators that are likely to feed on the Namaqua dwarf adder, Bitis schneideri, and used field surveys to assess their relative abundance.We used literature records to map the feeding preferences of avian species, and point counts to estimate relative abundance. Finally, we produced an index of relative predatory pressure (RPP) to assess the relative importance of each avian species as predators. We counted 490 individual birds from 30 species during 39 point counts. A cluster analysis of similarity between diets produced a dendrogram that we split into three functional groups: specialist predators, generalist predators, and non-predators. Specialist predators and generalist predators made up a total of 10.6% of the entire community by abundance. Generalist predators are likely to be the most important predators of Namaqua dwarf adders.We also noted an increased abundance of anthropophylic species outside our study site and suggest that anthropogenic areas could provide regions of increased predation pressure on small vertebrates.

African Zoology 45(2): 309–314 (October 2010)