Two swallows ride the insect hatch

The air above Montrose Beach fills with wings. Bank swallows and northern rough-winged swallows cut back and forth through invisible columns of insects, their flight paths mapping what we cannot see. The longest days of the year bring the richest feeding, and these two species work the same airspace with different techniques.

Bank swallows hunt in tight flocks, twenty or thirty birds wheeling together through the thickest swarms. They are smaller than their rough-winged cousins, built for quick turns and sudden dives. Their white bellies flash as they bank sharply, following the shifting columns of midges and mayflies that rise from the warming lake. The rough-winged swallows hunt alone or in pairs, taking longer, steadier passes through the air. They are slightly larger, with duller brown backs and no distinct breast band, built for sustained flight through scattered prey.

Both species time their nesting to this abundance. The aquatic insects emerging from Lake Michigan now spent the winter as larvae on the lake bottom, growing through the cold months. As water temperatures climb past twenty degrees, they begin their synchronized ascent. Midges rise first, followed by mayflies, then caddisflies. Each species emerges in pulses that last days or weeks, creating layers of opportunity that the swallows exploit. The bank swallows, nesting in colonies carved into the sandy bluffs nearby, feed their young on this protein-rich harvest. The rough-winged swallows, nesting singly in crevices and culverts, do the same. Different nesting strategies, same food source.

The swallows take insects of different sizes. Bank swallows specialize in the smallest prey, snatching midges and gnats that cluster in dense clouds. Their bills are narrow and precise. Rough-winged swallows take larger prey, including the mayflies and caddisflies that bank swallows often ignore. This division reduces competition between the species, allowing both to thrive in the same airspace. The insects themselves represent months of lake productivity concentrated into a few weeks of flight. Each midge carried back to a nest cavity contains algae and detritus processed on the lake bottom, energy transferred from water to air to the next generation of swallows.

Watch the light catch their wings as they turn. The bank swallows move like a single organism, the flock contracting and expanding as it follows the insect swarms. The rough-winged swallows trace longer arcs, covering more territory with each pass. Both species will feed like this until the last insects of the day settle back toward the water, then return at dawn to do it again. The longest days mean the most hunting time, and these are the days that fuel the breeding season.