Ecological Relations of Sympatric Black-Capped and Mountain Chickadees in Southwestern Alberta

In an attempt to determine the factors permitting sympatry of Black-capped Chickadees (Parus atricapillus) and Mountain Chickadees (P. gambeli) in southwestern Alberta, we examined nest-site utilization and foraging behavior during the summers of 1982 to 1984. Characteristics of both the nest tree itself, and the surrounding habitat, differed significantly between nest sites of the two species. Patterns of reuse of nest sites and behavioral observations suggested that some interspecific competition for nest sites may occur, but is probably not important. Foraging behavior differed significantly between the two species, suggesting that Black-capped and Mountain chickadees do not compete for food during the breeding season. Differences in habitat use by the two species apparently provide ecological segregation, and their coexistence on our study area is due to the mosaic nature of the habitat.