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.