Call similarities among mixed species flock associates

Certain calls of two species of parids, bridled titmouse (Baeolophus wollweberi) and Mexican chickadee (Poecile sclateri), are compared with those of some heterospecific flock members during the non-breeding season. Marked similarities occur in acoustic structure, and in some cases patterns of call delivery, between calls of the parids and some flock associates. A call of the Mexican chickadee, golden-crowned kinglet (Regulus satrapa) and brown creeper (Certhia americana) are very similar, with another Mexican chickadee call resembling that of the ruby-crowned kinglet (R, calendula.) and a bridled titmouse call. Marked resemblance also occurs between the titmouse and a ruby-crowned kinglet call. The evolutionary basis for the similarities is unknown, but vocal similarities may facilitate certain interactions, such as mobbing, in mixed species flocks.