The effect of shade tree species on bird communities in Central Kenyan coffee farms

Shade coffee has been recognized as a well-studied example of a land-sharing management strategy that both creates habitat for tropical birds while also maintaining agricultural yield. Despite the general consensus that shade coffee is more “bird-friendly” than a sun coffee monoculture, little work has been done to investigate the effects of specific shade tree species on bird diversity and their capacity to help deliver ecosystem services. Previous studies in temperate regions have demonstrated that due to shared evolutionary histories, native plant species are better at promoting native arthropod numbers, which in turn support a greater number of birds. This study investigated bottom-up effects of two shade tree taxa - native Cordia sp. and introduced Grevillea robusta - on insectivorous bird communities in central Kenya. Results indicate that foliage-dwelling arthropod abundance and the richness, and overall abundance of foraging birds were all higher on Cordia than on Grevillea. Furthermore, multivariate analyses of bird community data indicate a significant difference in community composition between the canopies of the two tree species, though the communities of birds using the coffee understory under these shade trees were similar. In addition, both shade trees buffered temperatures in coffee, which could help slow the growth of insect pests, and this was more pronounced under Cordia. These results suggest that native Cordia trees may be better at mitigating habitat loss and promoting ecosystem services in Kenyan coffee systems. Identifying differences in prey abundance and preferences in bird foraging behavior aids in developing region-specific information to optimize functional diversity, ecosystem services, and the conservation of birds in agricultural landscapes