Spatial and temporal variation in fruit and fruit-eating birds in the Taita Hills, south-east Kenya

Abstract

We studied the spatial and temporal variation in fruit abundance and frugivorous bird densities in a large-sized (135ha), a medium-sized (95ha) and five small-sized (each 2–8ha) forest fragments in the Taita Hills, Kenya. The large and medium patches were respectively divided into six and three plots, while the small patches were each treated as a single plot. A pilot analysis established that the plots were sufficiently independent. Three separate census-rounds were conducted in all plots. We found significant variation in fruit density amongst the three fragment-size categories, but no significant temporal variation. Five 'common frugivores' provided sufficient data for detailed analyses. Spatially, we found significant variation in their densities, but no significant temporal variation. Overall, frugivore numbers did not appear to track fruit supplies across different fragments over time. These findings suggest that the distribution and movements of birds were most likely related to, and/or limited by, other factors such as nesting needs and fragmentation effects rather than fruit. The absence of long-distance resource tracking suggests a lack of long-distance dispersal, which implies (along with obvious ramifications for gene flow) minimal chances for recolonisation following local extinctions for tree species that depend on these birds for seed dispersal.