Effects of crop diversity on bird species richness and abundance in a highland East African agricultural landscape

Abstract

We examined the effects of crop diversity on avian species richness and abundance in the highland farmlands of Nyandarua, Kenya. We surveyed birds using point counts and recorded habitat data at the same locations estimating cover and growth stage of all crop types, whether they were grown as intercrops or monocrops, and the dominant surrounding vegetation type. An index of crop diversity was calculated from the percentage cover of the different crop types. The effects of these habitat variables on bird species richness, abundance of foraging guilds and the abundance of each of the 12 most common species were examined using linear mixed models. Crop diversity had significant positive effects on species richness. Cereal cover had negative effects on species richness, overall bird abundance and abundance of granivores. Occurrence of cultivation/fallow and mixed vegetation as the dominant habitat surrounding crop plots positively influenced granivores’ abundance, and the abundance of Speckled Mousebird Colius striatus, a pest species, was favoured by increasing orchard cover and occurrence of wooded and shrub vegetation as the dominant surrounding vegetation type. The study confirmed that heterogeneity brought about by increased crop diversity and reduced cereal cover within cultivations contributed to enhancement of farmlands as habitats for birds.