VCE's final summer field session on Mt. Mansfield Tuesday evening started on a rough note, as a torrential downpour caught us off-guard while we were out setting mist nets. However, we gradually dried out with the steadily improving weather, and yesterday morning was productive. Most montane forest nests have clearly hatched, if not fledged, and vocal activity of all species was more pronounced than during the previous 2-3 weeks. We mist-netted or observed fledglings of Blackpoll and Yellow-rumped warbler, Dark-eyed Junco, White-throated Sparrow, and American Robin. We were surprised to capture 4 juvenile and apparently independent Hermit Thrushes, which do not breed on the ridgeline. Other mist net captures included 11 Bicknell's Thrushes -- 4 unbanded males, 6 birds that we had already captured earlier in the season, and one 6 year-old male with a solar geolocator that had managed to elude us all summer.In addition to free-flying juveniles, signs that the avian nesting season is waning included several females of different species with regressing brood/incubation patches, and a number of adult birds in the early stages of flight feather molt. Most migrant songbirds fit their annual molt (an energy-intensive undertaking) between the end of breeding and departure for fall migration, so finding thrushes and warblers with their innermost primaries missing is a sure sign of things to come. By the end of this month, the montane forest will be a quiet place, as vocalizing becomes scarce and adults lay low while in heavy molt.
We'll make a final foray to Mansfield in early to mid-September, when Bicknell's Thrushes typically show a brief resurgence of activity, including calling and singing, before they head south later in the month or during early October.
Chris Rimmer and Kent McFarland
Photo: Kent beaming upon recovering another solar geolocator from a Bicknell's Thrush on Mt. Mansfield; courtesy of Melissa MacKenzie
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