One individual was recaptured twice: a male Myrtle Warbler that was originally captured on 25 April 2008 in its 2nd-year was recaptured on 10 April 2009 and again on 17 April 2010.
One bird that was banded at SBL was recaptured offsite: originally banded as a 2nd-y male Myrtle Warbler on 17 April 2008 at SBL and recaptured >1 y later on 4 May 2009 at Whitehorse, Yukon.
4% of the Myrtle Warbler catch from mid-March through mid-April (the peak in molt frequency) and included the entire sequence of the molt process.
The majority of the birds undergoing prealternate molt were males, and the percent of molting birds that were males was comparable in the 2 subspecies groups: Audubon's Warbler = 71%, Myrtle Warbler = 79%.
Coupled with the record of recaptures and the progress of fat accumulation, the data are consistent with the hypothesis that the Myrtle Warbler is using the Portland, Oregon, area as a migratory stopover site for undertaking its prealternate molt and the subsequent accumulation of fat needed for its further migration.
A possible interpretation for the apparent pattern of molt-migration in the Myrtle Warbler is that it may result from a higher relative cost of molt possibly associated with nutritional quality of their food resources on the wintering grounds as opposed to the Willamette ValleyPuget Trough.
Audubon's and Myrtle Warblers were originally considered separate species but were combined by the American Ornithologist's Union (AOU 1973) based on Hubbard's (1969, 1970) study of phenotypic variation across their zone of hybridization.
Both subspecies groups showed this relationship, but because the molt was much more extensive in Myrtle Warblers, the relationship was more pronounced (Fig.
Although small numbers of Myrtle Warblers occur regularly during the winter at SBL, their primary wintering area is in coastal southern Oregon to central California (Janes 2003; Dunn and Garrett 1997).
The occurrence of both opposite season (spring-spring and fall-fall) and alternate season (spring-fall and fall-spring) recaptures indicates that the migratory path through Portland was a two-way one, at least for the Myrtle Warblers and hybrids.