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Flock structure and dynamics in the hybrid zone between black-capped chickadees (Poecile atricapillus) and Carolina chickadees (Poecile carolinensis) in southeastern Pennsylvania

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Description: Black-capped Chickadees ( Poecile atricapillus ) and Carolina Chickadees ( P. carolinensis ) hybridize along a narrow parapatric contact zone. At Hawk Mountain Sanctuary (HMS), Pennsylvania, most resident chickadees are Black-capped; however, the hybrid zone is moving northward such that hybrids are now present. In a prior aviary study, Carolina Chickadees were socially dominant over Black-capped Chickadees, suggesting that dominance could drive in the contact zone's movement, but whether this mechanism operates in the field was untested. I studied dominance hierarchies, integration of irruption birds (winter-visiting Black-capped Chickadees) into flock dynamics, and breeding biology at HMS in 2005-2007. Resident and irruption birds were similar in size, shape, or persistence at feeders; dominance patterns were unclear. In 2006, mixed pairs had lower hatching success than pure Black-capped Chickadee pairs, but no trend with increasing hybridization was evident. Full resolution of the role of social dominance in chickadee hybridization will require additional field study.
Language: English
Format: Degree Work