The response of birds and mixed-species bird flocks to human-modified landscapes in Sri Lanka and southern India

While there is no substitute for undisturbed forest, secondary forests and agroforests are increasinglycommon in tropical areas and may be critical to conservation plans. We compared the diversity andabundance of birds and the characteristics of mixed-species bird flocks in forests inside protectedreserves to ‘‘buffer’’ areas, consisting of degraded forests and non-native timber plantations at reserveboundaries, and to agricultural areas. We monitored a network of 57 transects placed over an altitudinalgradient (90–2180 masl) in Sri Lanka and southern India, collecting 398 complete flock observations and35,686 observations of birds inside and outside of flocks over two years. Flocks were rarely found in agri-cultural areas. However, the density of flocks in buffer areas was similar to that in forests, although bufferflocks were smaller in average flock size and differed significantly in composition, as measured by theproportion of species that were classified, from the literature, as forest interior or open-landscape species.While flock composition was distinct between agricultural, buffer and forest areas, the differences in thecomposition of flocks was not as great as the differences between the overall communities in thesedifferent habitats. Considering buffer transects alone, pine plantations retained fewer forest interiorspecies in flocks than did forests, and small areas of agriculture and abandoned agriculture attractedopen-landscape species. Though clearly not equivalent to protected forests, degraded forests andagroforests in buffer areas still hold some conservation value, with forest species found particularly inmixed-species flocks in these human-modified habitats.