A Study of Heterospecific Flocking and Nonbreeding Bird Community Structure of Rajaji National Park

Abstract

Many workers have found a direct relationship between bird community structure and vegetation structure. To investigate this and describe the heterospecific flocking behaviour of nonbreeding birds I sampled five habitat types in the Dholkhand range of Rajaji National Park, U.P., India. Inter-habitat differences in flocking and bird community structure were considered. I used the line transect technique to sample bird communities. Mixed species flocks were observed to investigate why birds flock. The guild structure based on diet and foraging strategy showed a marked difference between habitats. Species richness was estimated using rarefaction analysis, a procedure that standardizes the unequal area of the different sites. I used a correlational approach to answer the question – what determines bird species richness ? Foliage height diversity, canopy cover, canopy height, canopy height difference, tree density, tree species numbers and cross sectional area, were used as the vegetation variables. Results indicate that none of the variables have strong predictive value though tree species number which is the only floristic measure of the habitats has a consistent influence independent of sample size. The guild structures suggest that the bird communities vary with floristic aspects, of the habitats. To test my hypothesis that flocking is a response to food availability I related bird densities, which is an indicator of food availability, to flocking tendencies and found a inverse relationship. I also found behavioural evidence to suggest that flocking is also an anti-predatory strategy.