BIRD ASSEMBLAGES IN SECOND-GROWTH AND OLD-GROWTH FORESTS, COSTA RICA: PERSPECTIVES FROM MIST NETS AND POINT COUNTS

Second growth has replaced lowland forest in many parts of the Neotropics, providing valuable habitat for many resident and migrant bird species. Given the prevalence of such habitats and the potential benefit for conservation of biodiversity, it is important to understand patterns of diversity in second growth and old growth. Descriptions of species-distribution patterns may depend, however, on method(s) used to sample birds. We used data from mist nets and point counts to (1) describe species diversity and community composition in second-growth (young and old) and old-growth forests at La Selva Biological Station, Costa Rica; and (2) to evaluate perspectives on community composition provided by the two methods. We recorded 249 species from 39 families, including 196 species captured in mist nets (10,019 captures) and 215 recorded during point counts (15,577 observations), which represents ∼78% of the terrestrial avifauna known from La Selva (excluding accidentals and birds characteristic of aquatic or aerial habitats). There were 32 threatened species, 22 elevational migrants, and 40 latitudinal migrants. Species richness (based on rarefaction analyses of capture and count data) was greatest in the youngest site. Latitudinal migrants were particularly common in second growth; elevational migrants were present in both young and old forest, but were more important in old-growth forest. Several threatened species common in second growth were not found in old-growth forests. Trophic composition varied less among sites than did species composition. Mist nets and point counts differed in numbers and types of species detected. Counts detected more species than nets in old-growth forest, but not in young second growth. Mist nets detected 62% of the terrestrial avifauna, and point counts detected 68%. Fifty-three species were observed but not captured, and 34 species were captured but not observed. Six families were not represented by mist-net captures. Data from mist nets and point counts both support the conclusion that second-growth vegetation provides habitat for many species.