Managing tropical agroforestry for conservation of flocking migratory birds

Agroforestry systems have great potential to conserve biodiversity in highly-altered tropical landscapes. Although certain types of agroforestry, such as shade-coffee and cacao, are well known to support a diverse assemblage of resident and migratory birds, the ability of silvopastures to contribute to bird conservation is poorly understood. Important physiognomic differences among agroforestry systems suggest that the most effective habitat management strategies to support migratory birds may likewise differ. We surveyed two common agroforestry systems, shade-coffee plantations and silvopastures, in the Colombian Andes from 2011 to 2013 to identify which physiognomic features were most heavily associated with use by mixed-species flocks and migratory birds. Contrary to our expectations, the same management strategies may perform well in both systems. Flock activity increased with increasing canopy cover and tree density in both shade-coffee and silvopastoral systems. In addition, abundances of several migratory bird species within flocks increased with tree basal area and structural complexity, indicating that complex agroforests with a mid-range of canopy cover will provide the most suitable habitat for migrants attending mixed-species flocks. Our study suggests that suitability of shade-coffee and silvopastoral systems can be improved for overwintering migrants by increasing canopy cover to 25-40 % and incorporating emergent shade trees to produce a basal area of > 5 m(2)/ha.