Maintenance of bird functional diversity in a traditional agroecosystem of Madagascar

In Madagascar, despite acute land use pressure on forests coupled with unprecedented loss of endemic species and natural habitats, data on species distributions outside natural habitats are strikingly scarce. In this study, this gap is addressed by measuring bird diversity both within a protected forest corridor, and in the agricultural mosaic surrounding it. Results show that the diversity of all birds, and also of several functional guilds was higher in the mosaic than in the corridor. Moreover, 69% of all species found in the forest (61% of those classified as forest species) also occupied the agricultural mosaic. The diversity of frugivores, canopy insectivores and forest species in the mosaic was highly dependent upon the variety of scattered trees, small forest patches, plantations and secondary habitats distributed throughout the landscape. Generalist frugivores were particularly abundant in the mosaic, implying high potential for the maintenance of seed dispersal and fallow regeneration ecosystem services. Forest species in the mosaic were more generalist and less abundant, however, than those in the forest, suggesting the presence of both source–sink dynamics and potential biotic homogenization of the community in this landscape. Although under current conditions of heterogeneity and composition, the agricultural mosaic harbors a significant proportion of the endemic bird community, this study confirms the need for both sustained protection of large forest areas, and for adequate management of the agricultural landscape, particularly through the maintenance and enhancement of old-growth and isolated tree structures and fragments.