RESIDENCY, PAIRING, PRIMARY HYBRIDIZATION, AND BACKCROSSES

Males were considered as a resident at each study area if they were heard or seen on at least three days over a week’s span of time within an area approximately the size of Vermivora spp. territories (e.g., Confer et al. 2003). Almost all males were seen over a much longer period. Following the methods of Will (1986) and others (Confer et al. 2003, Vallender et al. 2007, Canterbury 2012), we considered males to have formed a pair with a female if they were observed feeding nestlings or fledglings or if they were seen on a perch close to the nest on several occasions. We considered pairing attributes for a banded male that returned to breed in another year as an additional, independent event.
Conspicuous singing with Type 1 calls from one or a few song posts (Gill and Murray 1972a) by paired or unpaired males provides a strong clue about the location of an established or desired breeding territory. After searching on three mornings for a total of at least six hours and spanning at least a week, a male was thought to be unpaired if no evidence of nesting was found near such song posts. Females are very cryptic, and almost all observed females were engaging in reproductive activities (e.g., nest building, carrying food, and alarm behavior). This provides a very biased sample of the proportion of females that are paired. Consequently, we estimated pairing success rates only for males. We quantified the pairing success rate at each study area as the fraction of the resident males that formed a social pair averaged for all years of each study. We equate primary hybridization to the formation of a social pair between phenotypes of Golden-winged and Blue-winged warblers.