Bird assemblages in the southernmost forests of the world: methodological variations for determining species composition
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2000
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Durante el verano del año 2000 se investigó la avifauna de bosques costeros de Magallanes,
Chile, en dos sitios de estudio: la península Antonio Varas (52°S) y la isla Navarino (55°S). En cada sitio, se investigó la composición de especies de las comunidades de aves por medio de redes de neblina, estaciones de observación/escucha a lo largo transectos y listados de todas las especies observadas -incluyendo aquellas detectadas fuera de transectos. Luego, se compararon los resultados obtenidos con cada metodología, como también con listas de especies elaboradas a partir de revisión bibliográfica. Nuestras listas de especies incluyeron el 95% de las especies documentadas y para Navarino se detectó la presencia de dos especies no registradas previamente: Colorhamphus parvirostris y Sephanoides galeriius. Los métodos de captura con redes de neblina y censos en transectos detectaron sólo parte del total de especies de aves, pero detectaron las importantes variaciones de abundancia entre ellas. Las comunidades de aves de Magallanes presentaron menos especies que las de bosques chilenos en latitudes más bajas, confirmando anteriores propuestas acerca de la disminución de especies de aves con el aumento de latitud en estos bosques. También ocurren variaciones en la abundancia relativa
de las especies. Por ejemplo, el picaflor es la especie más abundante en bosques de Chiloé, mientras que en Magallanes nunca superó el 5%. Otras especies (e.g. Elaenia albiceps, Turdus falcklandii, Aphrastura spinicauda y Phrygilus patagonicus), sin embargo, presentaron abundancias relativas similares. Se compararon también las comunidades de aves en tres tipos de hábitats: interior de bosque, margen de bosque y terrenos abiertos. Los dos últimos tipos de hábitat tuvieron mayor número de especies y abundancia de aves, e incluyeron especies características del interior de bosque. Este resultado debe ser cuidadosamente interpretado a la escala de paisaje, puesto que las áreas abiertas por actividad humana se encuentran inmersas en una región donde todavía quedan vastas extensiones de bosque primario.
During the austral summer of 2000 we studied the avifauna in coastal forests of Magallanes, Chile at two study sites: Peninsula Antonio Varas (52°S) and Isla Navarino (55°S). For each of these sites we investigated the species composition of the woodland bird assemblage through mist-nets, point-count stations along transeets, and all observed species, including observations outside of the transeets and/or mist-nets. Then, we compared the results obtained by each method, as well as with species lists obtained from bibliographic sources. Our species lists corresponded to 95% of bibliographic accounts. At Navarino we detected the presence of two species which were previously unreported: Colorhamphus parvirostris and Sephanoides galeritus. Transect and mist-net methodologies accounted for just part of the bird species assemblage, but addressed the important variations in abundance among species. Compared to avian assemblages recorded in Chilean forests at lower latitudes, the Magellan area contains fewer species. This confirms previous statements about the decrease in bird species with increasing latitude along these forests. There are also some major changes in relative abundance of species. For example, the hummingbird S. galeritus is the most abundant species in forests at Chiloé, but in Magallanes it was never greater than 5%. Other major species (e.g. Elaenia albiceps, Turdus falcklandii, Aphrastura spinicauda, and Phrygilus patagónicas) actually remain very similar as compared to Chiloé. We also compared bird assemblages of three types of habitats: forest interior, forest border, and open areas. These last two habitat types hosted greater abundance and species richness, including birds that are characteristics of forest interior habitats. This result needs to be carefully interpreted at the landscape level, because areas opened by human activity in Magallanes are still embedded in a region that conserves large expanses of primary forest.
During the austral summer of 2000 we studied the avifauna in coastal forests of Magallanes, Chile at two study sites: Peninsula Antonio Varas (52°S) and Isla Navarino (55°S). For each of these sites we investigated the species composition of the woodland bird assemblage through mist-nets, point-count stations along transeets, and all observed species, including observations outside of the transeets and/or mist-nets. Then, we compared the results obtained by each method, as well as with species lists obtained from bibliographic sources. Our species lists corresponded to 95% of bibliographic accounts. At Navarino we detected the presence of two species which were previously unreported: Colorhamphus parvirostris and Sephanoides galeritus. Transect and mist-net methodologies accounted for just part of the bird species assemblage, but addressed the important variations in abundance among species. Compared to avian assemblages recorded in Chilean forests at lower latitudes, the Magellan area contains fewer species. This confirms previous statements about the decrease in bird species with increasing latitude along these forests. There are also some major changes in relative abundance of species. For example, the hummingbird S. galeritus is the most abundant species in forests at Chiloé, but in Magallanes it was never greater than 5%. Other major species (e.g. Elaenia albiceps, Turdus falcklandii, Aphrastura spinicauda, and Phrygilus patagónicas) actually remain very similar as compared to Chiloé. We also compared bird assemblages of three types of habitats: forest interior, forest border, and open areas. These last two habitat types hosted greater abundance and species richness, including birds that are characteristics of forest interior habitats. This result needs to be carefully interpreted at the landscape level, because areas opened by human activity in Magallanes are still embedded in a region that conserves large expanses of primary forest.
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Avifauna, Censos de aves
Citación
Anales del Instituto de la Patagonia, Vol. 28, pp. 89-100, 2000