Where do the migrants hide during the day? And why don’t pewees go there?
We’ve all had that experience: a great morning chock full of migrant birds, but come 10:00 or 11:00 AM and it’s like somebody flipped the ‘Off’ switch. Where did all those migrants go? Landbird migrants tend to disappear in the late morning, and they become extremely difficult to locate after that time. In the morning, they’re usually actively feeding, so the assumption has been that once they’re filled up, they settle into the thick shrubbery to wait for nightfall, when they can start migrating again. Both observation and radio-tracking suggest that most small insectivores spend only a few hours feeding in the morning before settling down, usually out of sight. The hidden assumption is that they get enough food in the morning that they need not risk feeding throughout the day and further exposing themselves to predators.
Not all birds follow this pattern, though. Some are ultra-secretive and hide even during the morning – black-billed cuckoos and Gray-cheeked Thrushes are like this. You just don’t see much of those species on migration. On the other hand, daytime migrants don’t follow this pattern either, but in a different way. Flocking fruit-eaters like Robins and Waxwings seem to stay visible, if not active, throughout the day. Aerial insectivores like swallows are also obvious, even when they’re resting on wires between feeding bouts. And then there are Wood Pewees. These unprepossessing little flycatchers are nocturnal migrants, but still seem to stay active throughout the morning and into the afternoon. Not only that, but many of them are calling, so they’re doubly easy to locate. This Fall, so far, E.Wood Pewees have been the most common migrant landbird species on over half of my field trips (as I write this in early September).
Why might Pewees violate the pattern that seems so ubiquitous among small migrant landbirds? Part of it almost certainly has to do with their fly-catching habits. Unlike ground-pawing sparrows, fruit-eating thrushes, or leaf-gleaning warblers, wood pewees need to see and chase large flying insects. In late summer and Fall, the best place for these insects is the edge of woods or around water edges, where the warm sunlight makes them more active. Unlike warblers, which try to catch insects before they’ve warmed up too much, Pewees need insects already warm and active. This means that pewees can actively feed for much longer into the day than can warblers.
Another part of it must be due to the late calling. Pewees still call well into September, even when on migration. It’s possible that calling helps ward off other flycatchers so that they can feed undisturbed. They can be aggressive towards other insect-eating birds, chasing them and snapping at them with their bills. They certainly don’t join together into flocks like Kingbirds, nor do they join other species in mixed-species flocks, like some little Empidonax flycatchers. Some other flycatchers, like Myiarchus flycatchers (Great Crested and Ash-throated), have similar requirements and will also call during Fall migration. Wood Pewees, however, do not call much late in migration or on their wintering grounds. Growing up in south Florida, I rarely heard Pewees, even though they were a common late September-early October migrant and some even over-wintered. Perhaps defending their feeding space isn’t quite as crucial at these late stages in their migration.