Seasonal dynamics of a bird assemblage in a North Patagonian lenga (Nothofagus pumilio) forest and its relationship with the availability of foraging substrates

Abstract

We describe the seasonal dynamics of species composition and abundance of a bird assemblage in a lenga forest at Ñireco Valley, Nahuel Huapi National Park, Argentina, and the use of feeding substrates. Species diversity and density were lower in winter than in spring and summer. Species richness was minimum in winter but it has not variations in the other seasons. Most of the species present in winter (7 over 23) mainly used tree trunks and branches as feeding substrates. These substrates and their food supply are available during all the year. Birds that were absent in winter mainly used the soil, and to a lesser extent foliage and air as feeding substrates. Soil users can not overwinter in the area because although the soil contains food, it is covered in snow. Lack of food may determine the absence of foliage- and air-users in winter. Most species used a low number of substrates for feeding, mainly in fall and winter. Four species of high conservation value mainly feed on tree trunks and branches; it is possible that their winter survival depends on the availability of these substrates.