Trends in Richness and Occupancy of Ugandan Birds and Relation to Local Tree Cover

Abstract

Changes in vegetation cover are occurring across sub-Saharan Africa and can have substantial effects on ecological communities, but limited data make understanding status and trends difficult for many taxa. We surveyed birds for several decades across Uganda using point counts. Using time-to-detection analysis in a trait-informed Bayesian multi-species occupancy framework, we model bird species richness as a function of year and local tree cover across 28 sites. We test for trends in richness and occupancy, and for the relationship between these and local and landscape-scale tree cover. Species richness increased at 75% of sites through the study period, and generalist bird species were most likely to be increasing in occupancy. Forest specialist bird species, and to a lesser extent generalists, responded positively to tree cover. Woody cover is changing across Uganda, with declines most pronounced in areas with the highest tree cover. This is likely to be causing declines in forest specialist species while favouring generalists. When tree cover decline is caused by conversion to croplands, rather than transitions to grasslands, grassland specialists are unlikely to benefit. Effects of climate and land use change and population pressure are likely to continue to alter woody plant cover and thus affect East African bird communities.