Response of non-grassland avian guilds to adjacent herbaceous field buffers: Testing the configuration of targeted conservation practices in agricultural landscapes

Abstract

A substantial part of the world's land base is dominated by agriculture, and forest habitat often consists of discrete patches of forest and linear woody corridors. These natural components provide habitat for some forest birds, but make conservation of these species difficult. In-field practices applied outside forest patches, such as specific juxtapositions of herbaceous field buffers adjacent to forest habitat, could increase avian diversity contributions of existing forest without creation of additional forest habitat. Our prediction was that herbaceous field buffers would increase bird richness in adjacent forest, and we evaluated four potential mechanisms. We used bird count data from a conservation buffer monitoring programme and hierarchical community models to estimate species richness of forest generalist, forest interior and shrubland (edge) species near forest edges with and without adjacent herbaceous field buffers. We accounted for heterogeneity in detection probabilities and forest cover in surrounding landscapes when estimating species- and guild-level responses. Consistent with the drift fence hypothesis, adjacent herbaceous buffers were associated with a modest increase in richness of forest interior birds in woody corridors, but not in forest blocks. Consistent with resource complementation, adjacent herbaceous buffers were associated with modest increases in richness of shrubland (edge) birds in both woody corridors and forest blocks. Across all species and guilds, adjacent buffers were generally associated with greater abundance (e.g. 28 of 39 species), but these increases were also relatively small and highly variable (i.e. overlapping 95% credible intervals). Corroborating existing research, effects of adjacent herbaceous buffers are likely real, but neither pervasive nor strong. Synthesis and applications. Conservation practices targeted to grassland species often produce measurable conservation benefits for target species. However, biodiversity return for investment would be further increased if targeted practices could be deployed in ways that also produce benefits for non-target species in adjacent habitats. Our results suggest that additional benefits for non-target species using adjacent forest habitat are likely to be modest, so conservation planning should focus on species targeted by the conservation practices and avoidance of potential negative impacts on those species when positive benefits to adjacent habitat are weak or lacking.