Number observed: 4
Details: Observed 4 adults flying and aerially feeding in a large mixed flock, including Vaux's Swifts, Violet-green Swallows, Tree Swallows, and Barn Swallows. Over residential and mixed habitat, open lakeshore. Accepted by MBRC (#2008-034); here is part of the narrative in my report to them:
They were visibly longer-winged and flew differently than the Vaux’s Swifts feeding in the same airspace. But they were not large enough to be Black Swifts, and were not black. Their wing-flapping was not as “languid” as Black Swifts, either. As one who is intimately familiar with these two expected species, the differences noted in the birds’ flight habits were obvious. There was no white in the plumage, nor were they quite as streamlined (thin-winged) as White-throated Swifts. I gave no serious consideration to Eurasian swift species, all of which have white throats and/or noticeably long forked tails. The key for me on this identification is that it took me by surprise, and I questioned myself as I could not make these birds either Black Swifts (80 of which were seen in this same location a week earlier) nor Vaux’s Swifts. I was not looking for, nor expecting to find this species, or to be presented an opportunity to compare them directly with Vaux’s.