Though it falls short of May in the number of species of birds present, September probably brings the year’s largest raw numbers of birds, largely because adults are joined by juveniles, partly because lingering breeders are overlapped by arriving migrants from the north, but also because a number of species have fall migration routes that bring them to Ohio whereas their spring routes seldom do. Examples of the latter among shorebirds include buff-breasted/western/stilt/Baird’s sandpipers, and long-billed dowitchers. All the same, except among a few species, shorebird numbers generally decline by the end of the month. Eclipse-plumaged waterfowl predominate at this time. Rallids like coots, moorhens, and soras peak at this time, then quickly decamp. Immense flocks of migrating cormorants appear late in the month along the Lake Erie shore, continuing through October.
The first large passage of raptors now begins, with the greatest counts among those hemmed in and concentrated by Lake Erie’s waters; huge concentrations of certain species—ospreys, accipiters, and especially broad-winged hawks—have been recorded in September. Wintering raptors like harriers begin to appear, and gulls increase in numbers and variety, hinting at winter just as the big tern roosts thin out. The first movement of jaegers begins with flights of the quite rare long-tailed.
This is a peak time for most southbound thrushes, warblers, flycatchers, vireos, nighthawks, ruby-throated hummingbirds, and terns, though by no means have all passed by at the month’s end. To many species—certain waders, rails, a few shorebirds, cuckoos, nighthawks, hummingbirds, flycatchers, kingbirds, gnatcatchers, vireos, swallows, bobolinks—we mostly bid adieu in September, though there are some exceptional later records of all of them. Flickers stage conspicuous migrations late this month and into the next. Thrushes pass by night, with wood thrushes leading the way, then Swainson’s, then gray-cheeked, then hermits. Bright indigo buntings and tanagers begin molt before they depart, and odd piebald individuals confound some observers. Chimney swifts begin to form assemblages at urban sites, sometimes in the thousands, that continue into October.