Bird assemblage patterns in relation to anthropogenic habitat modification around an East African estuary

Abstract

Influences of human activities on habitat quality and subsequently, bird density and distribution were examined at an estuary along Kenya’s coastline. Using habitat stratification, birds were surveyed along transects in tidal and supralittoral sub-habitats using DISTANCE sampling protocol, and along the river by encounter rates to determine abundance and species richness. Indices of human activity as well as habitat structure parameters including ground cover, plant density, plant species richness and habitat heterogeneity, were also determined to examine their influence on bird dispersal and density. Together with river depth, water quality along the river was tested in terms of water transparency and pH. Crustaceans were also sampled across the study site including inside the river, to evaluate spatial abundance, distribution and correlation to bird dispersal. Four dominant forms of human activity were delineated, with random dispersion across the habitat strata. Overall, higher anthropogenic activity indices corresponded to low bird diversity and density though birds were denser in more vertically heterogeneous habitat zones. In the river, human activity showed no clear effect on bird abundance nor were bird and water quality variables significantly correlated directly. Abundance of crustacean mirrored that of shorebirds both in density (R=0.8095, p=0.0149) and species richness (R=0.6429, p=0.0856) along the river, but this appeared to be delimited by water pH especially in low-water level periods (t=3.536, p=0.0123). The results show that regulating human-induced activities around the estuary would secure its medium-term ecological integrity.