Wilson Warbler molting and plumage observations

I made observations of a central California population of Wilson’s Warbler, Cardellina pusilla, on or after 1 July over ten breeding seasons. I sighted males in definitive prebasic molt as early as 4 July (in 2007) and as late as 1 September (in 1999). I determined that most territorial males at my study site molted on their breeding territories, and individual molt lasted a maximum of 46 days. Following prebasic molt, territorial males engaged in subdued “post-molt singing,” which appeared to last no more than seven days in most males, and which I first heard on 13 August (in 1004), and last heard on 6 September (in 1999). I sighted no female in definitive prebasic molt, nor fresh basic plumage, during the study. Of 13 females sighted on or after 21 July, I confirmed that 11 were in late breeding season uniparental brood care, and I could not rule out late brood care for the other two. Most, and possibly all, females not engaged in late season uniparental brood care appear to have vaca...