How Convergent Is the American Redstart (Setophaga ruticilla, Parulinae) with Flycatchers (Tyrannidae) in Morphology and Feeding Behavior?

Abstract

ABsTRAcr.-Possible convergence between the unique aerial-feeding American Redstart (Setophaga ruticilla) and the tyrannid flycatchers was considered using skeleton, external morphology, substrate use, and locomotory feeding movements. The redstart is a typical paruline in the broader functional units of forelimb, hindlimb, and body axis, as well as in proportionate lengths of the main axial elements of both the forelimb and hindlimb. It retains and utilizes the advantageous features of the wood-warblers, including the capacity to hop rapidly through the vegetation. To this it has added the long and broad bill, and long rictal bristes (adaptations for aerial feeding) of the tyrannids. The wing shape remains woodwarblerlike, but it is convergent with the flycatchers in its low wing loading. The tail is long, as in the flycatchers, for better aerial control, but is spread and, apparently, used to flush insects from vegetation, as in the specialized Australo-Papuan fantails (Rhipidura). The redstart is a unique adaptive and ecomorphological type among north American passerines. Received 30 March 1993, accepted 19 August 1993.