Mobbing in the pied flycatcher. Effect of experiencing a live owl on responses to a stuffed facsimile.

A surprisingly high proportion (42%) of breeding pied flycatchers failed to mob a stuffed pygmy owl placed near the nests. To determine whether the range of effective stimulus objects eliciting mobbing could be extended in these "non-mobbers", a live owl, resembling the ineffective dummy in nearly all static owl traits, was briefly exposed. It evoked strong mobbing from all birds, as did the stuffed specimen on a subsequent presentation. The role of experience with live predators and the effect of labile properties of the latter on the mobbing response are discussed.