Composition Changes in a Subandean Avifauna after Long‐Term Forest Fragmentation

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Abstract
Current understanding of the effects of forest fragmentation is based largely on studies in temperate regions, Australia, and Neotropical lowlands. In contrast, the consequences of anthropogenic forest fragmentation for Andean avifaunas are poorly understood, despite large‐scale habitat loss and fragmentation. I assessed the effects of long‐term fragmentation on a subandean avifauna in Colombia by comparing the occurrence of bird species in forest fragments isolated over 50–90 years with the original avifauna. Prefragmentation bird composition was based on historical records and current species composition in continuous forest. The original avifauna had approximately 139 forest species and 45 species of open habitats. Among forest species, 30% were currently extinct in fragmented forest and 4% were regionally extinct. At least 23 nonforest species colonized the region from the lowlands following deforestation. Species with small geographic ranges and those that were locally scarce or rare throughout their ranges were likely to be locally extinct. Forest raptors, terrestrial insectivores, and large frugivores were highly extinction prone, whereas nectarivores, small frugivores, and aerial insectivores were highly resilient; other guilds were intermediate. Antbirds (Formicariidae, Thamnophilidae), Cotingas, and, especially, Icterids were highly extinction prone. Large body size was not a determinant of vulnerability except among frugivores. Sixty‐two percent of the species of special conservation concern were extinct in fragments. These results suggest that only large forest tracts will ensure the survival of a large proportion of subandean avifaunas. Fragments of mature forest, however, may support a diverse avifauna, including small populations of globally endangered species several decades after isolation. These fragments could play an important role in the restoration of local avifaunas. A good understanding of the mechanisms that allow persistence in such fragments may prove essential for the conservation of those species for which no large tracts of suitable habitat remain.