Chimney swifts return to the leafed canopy

The canopy at Great Swamp has thickened into its full green presence. White oak and sugar maple leaves have expanded to catch the late spring light, and beneath them the understory has filled with the broad leaves of flowering dogwood and the delicate foliage of spicebush. Above this green ceiling, small dark shapes cut tight arcs through the air.

Chimney swifts have returned to breed, and they hunt now against the backdrop of this newly leafed forest. These threatened birds spend almost their entire lives airborne, feeding on flying insects that rise from the warming canopy below. Their wings beat in rapid, shallow strokes, different from the deeper wingbeats of swallows. They bank sharply, following the erratic flight paths of their prey with movements that seem to anticipate where an insect will be rather than where it is. A swift's mouth opens wide as it flies, creating a funnel that captures small moths, flying ants, beetles, and midges that emerge from the forest.

The timing matters. As the trees have leafed out, they have created habitat for countless insects that the swifts depend on. Aphids feed on the new maple leaves and take flight when disturbed. Small moths emerge from pupae that overwintered in the leaf litter below the oaks. Flying ants leave their colonies in the warming soil to establish new ones. The forest canopy acts as both nursery and launch pad for the aerial insects that sustain these birds through their breeding season. Each layer of leaves creates microclimates where different insects develop, and each warm afternoon brings new flights of prey into the air column above the trees.

The swifts nest in chimneys and other vertical structures, but they hunt here above the forest because this is where their food lives. A single swift can consume over a thousand flying insects in a day during breeding season, when adults are feeding both themselves and their young. They drink by skimming the surface of open water, and they even mate in flight, but it is the rich insect life rising from this diverse forest that draws them back each spring. Listen for their high chattering calls as they wheel overhead. The sound carries down through the green canopy that feeds the insects that feed the swifts, a chain of energy that begins with sunlight on new leaves and ends with these small, tireless hunters scribing their paths against the sky.