Niche organization of a forest bird community in north-western Italy during autumn and winter. A comparative analysis
ROLANDO A. and TECCHIATI F.Abstract:
The niche organization of a deciduous forest bird community (Passeriformes and Piciformes) in north-western Italy has been described by considering other activities in addition to foraging. Principal Component Analysis suggests that, with regard to foraging, the first factor (PCl) depends on the use of outer parts of branches and middle height of trees in autumn whereas it is mainly concerned with the use of trunk , ash and oak versus the ground in winter. As for singing , the first factor is highly correlated only with particular species of trees in autumn whereas it defines the use of the outermost parts of branches in winter. Such differences reflect well-known seasonal shifts in the behaviour of species. The lack of correlation between foraging and singing rotated loadings suggests that foraging community organization differs from the singing one. Cluster analysis (Pearson's distance) stresses the ecoiogicai isolation of woodpeckers both in autumn and in winter. Also tits and associated species are seen to be separate enough from others both in foraging and in singing. Dendrograms computed on data collected without distinguishing birds' activities are more similar to foraging dendrograms than to singing ones. This seems to suggest that in autumn and winter community organization is more dependent on foraging than on singing activities. Since the results of the Cluster analysis are in agreement with those previously obtained concerning the same data but worked out by simple niche overlap indices, it may be inferred that both methods of data analysis are adequate to describe community organization.