Flycatchers work the longest days

Along Herrick Brook in Pawlet, the air above the water is thick with wings. Mayflies are emerging, their adult lives measured in hours, and the flycatchers know it. The oaks and black cherries are in full leaf now, the canopy closed and deep, and the days are as long as they will get. This is the week when aerial insects are most abundant, and three species of flycatcher are working every layer of the air above the brook and the surrounding forest edge.

The least flycatcher is the smallest of the three, and the loudest per ounce. Its call is a sharp, emphatic che-BEK, repeated so insistently from the mid-canopy that it can seem like the only sound in the woods. If you are near any shrubby edge or second-growth stand, you are probably hearing one now. The least flycatcher hunts from a low perch, usually six to fifteen feet up, watching the space just above it. When a mayfly or small moth drifts into range, the bird launches, takes it in the bill, and returns to the same branch or one nearby. It does not chase far. The whole sequence takes less than two seconds, and then the bird is back, calling again.

Higher up, the great crested flycatcher works the canopy. It is a larger bird, olive-backed with a bright yellow belly and a rusty tail, and its call is a rising, raspy wheep that carries well through the trees. It hunts the same emerging insects but from twenty feet up or more, taking bigger prey when it can: larger mayflies, moths, the occasional dragonfly. Great crested flycatchers are cavity nesters, which ties them closely to mature trees with old woodpecker holes or natural rot pockets. They are nesting now, and the adults are making long, fast loops from the canopy to intercept anything that moves in the open air between the trees.

The eastern kingbird operates at the other end of the habitat, out in the open over the water and along the brook margins. It is a striking bird in black and white, with a thin red crown stripe usually hidden unless the bird is agitated. Kingbirds are aggressive and territorial, and they will pursue crows, hawks, even great blue herons that pass too close to a nest site. But their hunting is methodical: a perch on a dead branch or fence wire over open water, a scan of the airspace, a fast angled flight to intercept a flying insect, and a return. They take mayflies heavily during emergence events, and in early summer the brook corridor gives them exactly the combination they need: open water below, exposed perches above, and a continuous hatching of aquatic insects moving up through the light.

Mayflies spend most of their lives as aquatic nymphs, sometimes a year or more on the stream bottom, before climbing out of the water, splitting their nymphal skin, and taking flight as winged adults. The adult stage exists only to reproduce. Most mayfly adults do not eat at all. They mate, lay eggs, and die within a day or two, sometimes within hours. This compression of the adult phase into a narrow window is exactly what makes them useful to the flycatchers: the emergence is predictable in timing, concentrated in space near the water, and the insects are relatively slow and abundant. Three species of flycatcher, hunting at different heights and in different microhabitats, are each drawing from the same emergence event without competing directly with each other.

The eastern phoebe is also here, hunting low over the water from streamside rocks and root tangles, and barn swallows are working the open air above the meadow edges with a different technique entirely, staying airborne and sweeping continuously rather than returning to a perch. Each of these birds is tracking the same peak. The long days mean more hours of flight activity for the insects and more hunting time for the birds. Nests are full of young right now, and the adults are moving almost constantly.

Watch the air just above the water surface, if you are near the brook. The mayflies rise in a loose, drifting column, wings catching the afternoon light.