Aspects of the comparative behavior of red-eyed and Philadelphia vireos

Abstract

Specific postural and vocal displays in successive stages of the nesting cycle are compared between sympatric red-eyed and Philadelphia vireos based on 9 years of field studies in Ontario and elsewhere. Vireos reach northern Ontario between mid-May and early June. Territorial behavior, including crest-erect alert, head forward threat, tail-fanning, and gaping, are seen in both species but at different frequencies. Physical encounters include supplanting, circle chasing, pecking, and grappling. Epigamic behavior begins immediately in both with pair formation, which differs only in timing between the two species. Pairs are maintained by male and female wing-quiver, female squat, and male swaying displays. Swaying in red-eyed vireos involves feather erection, tail-fanning, and continuous asynchronous swaying of the body, head, and neck. Swaying is simpler in Philadelphia vireos. Intrapair aggression, displacement preening, and interruptions of courting birds by third adults are discussed. Special vocalizations: 'myaah' and warbling song (red-eyes) and 'ehhh,' 'bubble' song, and contact notes (Philadelphias) are discussed. Nest site selection and nest building are done only by females in both species. Philadelphia vireo males incubate; red-eyed vireo males do not. Males of both species feed nestlings and fledglings. Evolutionary implications of the display and behavioral patterns of the two species are discussed.