Isabell Riedl

Gallery forests in the lowland countryside of Costa Rica: Corridors for forest birds?

In this study I investigated the importance of gallery forest strips within landscapes dominated by strongly human-modified habitats to serve as corridors and stepping stones for tropical forest birds. Therefore bird assemblages were surveyed in forest interior, forest margin, gallery forest connected to, and gallery forest isolated from closed forest in the Pacific lowlands of the Golfo Dulce region (Costa Rica) in proximity to the village and the Tropical Field Station “La Gamba”. More than onethird of species found in gallery forest connected to closed forest were classified as forest species and nearly a quarter in isolated gallery forest. Species richness of forest understorey birds showed a dramatic decrease in gallery forests, particularly in isolated gallery forests, which harboured less than 10% of the forest species richness recorded in forest interior. Most of the range-restricted species could also be recorded in gallery forests, some even in remarkable abundance. Range-restricted species that did not occur in gallery forests included Trogon bairdii and Habia atrimaxillaris, the only two recorded bird species which are classified as endangered globally. The structure of feeding guilds remained relatively stable across surveyed habitats. A clear change of species richness and abundance between habitats was only found for granivores, which were rare in forest interior and most species-rich and abundant in isolated gallery forests. Although the majority of forest species can be regarded as restricted to closed forests, at least for a fraction of them gallery forests can potentially act as corridors or stepping stones for movements between forest fragments or may even represent suitable breeding habitats.