Bird assemblage mist-netted in an Atlantic Forest area: a comparison between vertically-mobile and ground-level nets

Mist nets may be opened at different heights in the forest, but they are seldom used over 3 m above the ground. We used two different methods to compare species richness, composition, and relative abundance and trophic structure of the bird assemblage at Ilha Grande (with a 290 birds standardization): conventional ground-level nets (0-2.4 m height range) and elevated nets (0-17 m) with an adjustable-height system (modified from Humphrey et al., 1968) that we call vertically-mobile nets. There were significant differences in capture frequencies between methods for about 20% of the species (Chi-squared test, P<0.05), and the two methods caught different assemblages. Ground-level nets recorded less species, and they comparatively overestimated mainly Suboscine insectivores and underestimated frugivores and nectarivores. Different sampling methods used at the same location may result in very different diagnoses of the avifauna present, both qualitatively and quantitatively. We encourage studies involving mist net sampling to include the upper strata to more accurately represent the avifauna in Atlantic Forest.