Birds are so diverse in Ohio during May that it is perhaps best to start by saying which species groups are largely absent at this time. Except for our relatively few breeders, swans, geese, and ducks have moved on by this time, as have loons and grebes, though a few individuals wounded by hunters, or immature birds failed by their hormones, may be found. Except for herrings, ring-bills, and the occasional non-breeding great black-backed, so have the gulls. Winter visitants like northern shrikes, a few sparrows, and the winter finches have departed, treating us to occasional songs during their last days here. Some wintering species that do not breed in Ohio still pass through well into May—white-crowned and white-throated sparrows, pipits, a few siskins, and rusty blackbirds prominent among them.
May is celebrated for the profusion of high-spirited full-grown would-be breeders that arrive here or pass through: bitterns and rails, moorhens and coots, shorebirds, terns, goatsuckers, swifts, hummingbirds, flycatchers, vireos, thrushes, warblers, tanagers, sparrows, grosbeaks, and orioles. Numerous and in their brightest plumages, often in best voice, they are often easy to find, observe, and identify. It is a time of high hopes and striving for the birds, and the spirit seems infectious among birders. It is easy to conceive of a dayís birding that would tally twenty-five warbler species, fifteen shorebird species, and a total of over 150 for a not-too strenuous outing, and in one all-out effort a May daily total of 205 has been reported.
Exciting as they always are, spring migrations are susceptible to considerable variation. Weather that helps the northward passage sometimes leaves birders flat-footed, as the birds they seek pass overhead easily and quickly—and often out of sight by night. Even if they are inconvenient and even dangerous for the birds, it is interruptions in the migratory flow that produce local concentrations birders welcome. A warm southerly airflow, encouraging movements north, that is suddenly, even violently, interrupted by a cold front can ground migrants in spectacular numbers. This sort of fall-out can be especially dramatic on the south shore of Lake Erie, whose tossing gray waters can be an additional disincentive to proceeding further. These occasions, when in prime stopover habitats colorful migrants in full song by the thousands stud the trees like holiday ornaments, are so remarkable that they linger in memory for a lifetime.
The schedule of migrants during May, absent very disruptive weather that might cause overflights, is normally a fairly orderly affair, and is well depicted in the OBRC Checklistís bar-graphs. Louisiana waterthrushes always arrive well ahead of northern waterthrushes. Yellow-throated warblers always precede yellow warblers. Wilsonís and orange-crowned warblers are highly unlikely on the same day. Yellow-throated vireos arrive three weeks ahead of Philadelphia vireos. Spring migration may seem riotous, but while there are occasional surprises it is never chaotic or disorderly.