Habitat partitioning by a rural bird assemblage in northern Chiloé Island (42ºS), Chile

Background/Question/Methods

Fragmentation of temperate rain forests due to the expansion of agriculture and forestry has greatly changed rural landscapes in southern South America. The extensive old-growth forests admired by Darwin 180 years ago have been converted into small patches of remnant forest, including secondary forests and shrublands, immersed in an anthropogenic matrix of grasslands, croplands and, more recently, non-native eucalyptus plantations for cellulose production. Land cover change may strongly affect habitat quality for wildlife. In this rural landscape, we evaluated how the structure and composition of forest bird assemblages varied among cover types, representing habitats of contrasting quality. We analyzed species richness and abundance of forest birds during the breeding season in three dominant habitat types (old-growth forest, riparian forest and shrubland) in the rural landscape of Chiloé Island. The study was conducted in the Chilean-LTER site (Senda Darwin Biological Station, 42°S) during the 2010-2011 breeding seasons (September-January).  Surveys were conducted using point-count method (10 points per habitat), with a radius of 25 meters each, separated by 130 m from one another. 

Results/Conclusions

Over the two years of study, bird species richness in all habitats was 39 species, including raptors and aquatic birds. The most abundant species over all sites and years were the migrant White-crested Elaenia (Elaenia albiceps; Tyrannidae), the Green-backed Firecrown (Sephanoides sephaniodes; Trochilidae) and the resident Austral thrush (Turdus falcklandii; Turdidae). Bird surveys did not show differences in the total number of species among old-growth forest, riparian forest and shrubland, throughout the breeding season. However, bird abundance (counts) was significantly higher in riparian forest in comparison the old-growth forests and shrubland. At the community level, the bird assemblage of old-growth forests differed from the assemblage of riparian forests and shrubland, while these two last habitats shared a higher number of species. We suggest that this difference is due to the presence of bird specialists in old-growth forest habitats, such as the Magellanic woodpecker (Campephilus magellanicus; Picidae). Our results highlight the function or riparian forests as biological corridors and habitat for birds in the grassland-dominated countryside. We show that rural environments, including small forest patches, maintain species richness and abundance of birds comparable to remnant large forest patches or continuous forest, suggesting a strong influence of the landscape mosaic on assemblage composition of birds in Chiloé.