As we turn in to late May, Ohio's birders start looking for special 'late' migrants. We avidly hunt for, and have fond memories of, elusive boreal forest birds making their brief stops here. A short list of these birds would include highly sought-after birds like Black-billed Cuckoos; Alder, Yellow-bellied, and Olive-sided Flycatchers; Philadelphia Vireo; Gray-cheeked, Swainson's & Bicknell's Thrushes; Cape May, Blackpoll, Bay-breasted, Connecticut, Mourning, Wilson's and Canada Warblers. Often a trip in late May – early June can be made memorable just by seeing 1 or 2 of these gems.
Why are they so rare? It's not that they're numerically scarce; each can be abundant on their Canadian breeding grounds. It's more about how they migrate. They're among the last Spring migrants (like many shorebirds), because they're bound for the northern part of Canada (also like many shorebirds). Most are obligate insect eaters, and they delay their migration presumably to avoid the late frosts that can decimate their food supply. So late do they migrate that some birders have taken to calling them “3rd wave”, to distinguish them from earlier temperate (1st wave) and broadleaf forest neotropical (2nd wave) migrants. Because their migration is so delayed, they are more prone to fly very long distances with fewer stops, so that they can overfly much of the continental U.S. on their way north.
Nightime flight call monitoring suggests that lots of these birds are passing over the eastern U.S. at night. Ground sightings are so unpredictable, however, that the birds must be fast flyers (passing over most of the U.S.) or great at hiding when they are grounded. Growing up in Florida, I rarely saw any of these birds as migrants unless we had a serious storm in mid-late May; then they could be found in spectacular fallouts, particularly in coastal forest patches. The same pattern holds here in Ohio. Bad weather forces them down, and they are much more common at our 'coastal forest patches': the migrant traps along the Lake Erie shore, like Maumee Bay, Magee Marsh, Sheldon marsh, and Headlands Beach. Overflights are so typical of these birds that they'll often be found at Magee Marsh or other Erie traps well before we find them in central Ohio.
How can we predict them and successfully look for them? Weather is obviously important; to maximize your chances you need to get out on cloudy or rainy mornings. If you don't want to make the drive to the Erie migrant traps, you'll need to be aware of these birds habitat preferences. Most migrants develop a keen sense of preferred habitat, sometimes as they migrate, and the 3rd wave is no exception. Their preferences may be even stronger because of their rush to breeding. Many of the 3rd wave birds have habitat preferences that help focus you for them. Olive-sided Flycatchers love dead snags around conifer trees (which is exactly the habitat they prefer in Canada), so conifer-rich sites like Greenlawn cemetery are good for them. Connecticut Warblers like moist thickets near water, while Mourning Warblers like 2nd growth edges of old forest cuts (like you often find in powerline or pipeline cuts). Gray-cheeked Thrushes are super-secretive in migration; even if they're grounded, they seek out the shadows of the densest thickets and are often given away only by their strangely harsh locator call, a soft 'kee-yerr'. Obviously, though, there is an element of chance in finding these birds. A mix of right weather, right habitat, and plain old luck can lead to a memorable sighting. That's part of the appeal of birding; you just can't predict what you'll find.