Description and Analysis of Breeding Habitats of the Chickadees, Parus Atricapillus and P. Rufescens

The breeding habitats of Parus rufescens and P. atricapillus are largely nonoverlapping. A multiple regression analysis was used to describe carefully their breeding habitats and to analyze the extent of their coexistence. The abundance of P. rufescens is most highly correlated with the percent of the upper story canopy volume which is coniferous and the average height of the upper story conifers; taken together, these 2 variables account for more than 90% of the variability in the observed abundances. For P. atricapillus, the canopy volume of all trees, all bushes, and middle story trees together most accurately predict its abundance; the regression of these 3 variables on abundance accounts for over 90% of the variability in the observed abundances of P. articapillus on the study areas. Evidence is presented which supports the view that it is these features of the habitat to which the chickadees respond in selecting a breeding habitat. On the San Juan Islands, from which P. atricapillus is absent, P. rufescens was seen to breed in a broadleafed area. On the mainland it was not seen to breed in a comparable situation. However, P. rufescens appears to be more abundant on the island, and this greater abundance may have caused some individuals to select the "vacant" broadleafed area instead of the preferred conifers. Further observations in the broadleafed trees on Vancouver Island are needed to test further the idea that the absence of P. Atricapillus from it and the San Juan Islands has led to a modification in the habitat selection mechanism of P. rufescens on these islands.