Diversity of bird communities on the north slope of Taibai Mountain in winter and spring

In the winter (November) of 2009, spring (April) of 2010, and spring (March and April) of 2011, a line transact method was adopted to investigate the bird communities along the north slope of Taibai Mountain, the summit of the Qinling Mountains in Northwest China. Based on the elevation and typical vegetation, six types of habitat were categorized, and representative sampling plots were selected for each habitat type. The relative abundance and estimated area were considered to calculate the relative bird density, and the dominant and common bird species were defined according to the density rank for each habitat type. Over the whole survey period with two seasons, a total of 121 bird species were recorded, belonging to 71 genera, 40 families, and 12 orders, among which, 92 species were residents, 24 species were summer breeders, and 5 species were passaging migrants. Both in winter and in spring, the birds in the habitats were mainly of resident species. There existed definite differences in the density and structure of bird communities in different habitat types within the same seasons and in the same habitat types between different seasons. There also existed differences in the composition of dominant and common bird species between different habitat types and different seasons. Among the habitat types, anthropogenic disturbed deciduous forest had the highest bird diversity index in both winter and spring, and deciduous forest had the highest bird evenness index in the two seasons. The similarity index was generally higher in adjacent habitats than in separate habitats. Except that the bird species number in the mixed forests at medium and high altitudes had somewhat increase over the previous adjacent vegetation type, the bird species richness decreased with increasing altitude, and the bird species composition had greater change, as compared with that between spring and winter.