Taxonomic Differences in Head Movements of Vocalizing Passerines

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Abstract
New observations of 41 passerine species reveal possible taxonomic differences in the occurrence of raising of the bill coincident with vocalizations. Such conspicuous bill-raising occurs in certain species in the Tyrannidae, Parulidae, Icteridae, Thraupidae, Cardinalinae and Emberizinae, but is apparently absent in certain other icterids and emberizines and perhaps in numerous other taxa. Closely related taxa among the parulids and among the emberizines share the bill-raising, and this behavior might constitute a useful systematic character, but many additional data are needed. The apparently scattered taxonomic distribution of bill-raising coincident with vocalization indicates that convergent evolutionary gain or loss of the behavior may have occurred at least occasionally. Raising of the bill might serve to modify the vocalization and/or as a visual display. Other head movements, not known to vary taxonomically, are discussed briefly.