Ecological Complementarity of Three Sympatric Parids in a California Oak Woodland

Abstract

Foraging site data for sympatric plain titmice (Parus inornatus), chestnut-backed chickadees (P. rufescens) and bushtits (Psaltriparus minimus) during 2 breeding seasons demonstrate a fine level of ecological segregation even though the 3 spp. appear to depend primarily on the same kind of food to rear their young. Site overlap between the bushtits and titmice is low, whereas the chickadees overlap substantially with each of the other 2 spp. Concomitantly, the chickadees show an intermediate niche breadth along almost all components of a foraging site niche axis, while bushtits and titmice are either broad-niched or narrow-niched with regard to particular components and exhibit striking complimentarity. The larger-than-expected chickadee territories probably result from competitive pressure at interspecifically shared foraging stations and the species'' lack of special adaptations for feeding in evergreen oaks. The data suggest that the chickadees'' invasion of central coastal California [USA] woodland communities is successful when the heterogeneity of the structural habitat is great enough to allow segregation of foraging sites.