Natural and Simulated Encounters between Sympatric Black-Capped Chickadees and Mountain Chickadees

We compared naturally occurring intraspecific and interspecific encounters between Black-capped Chickadees (Parus atricapillus) and Mountain Chickadees (P. gambeli) during the breeding season in a region of sympatry in southwestern Alberta. We observed chasing or supplanting, or countersinging by males, in all intraspecific encounters, whereas heterospecific individuals were ignored in 73% of interspecific encounters. In playback experiments conducted at nest sites, both species responded strongly to conspecific song but showed much weaker responses to heterospecific songs. These results support our previous conclusion, based on measurements of territory overlap, that these two species do not exhibit interspecific territoriality.