Chimney swifts hunting the insect rise

Above Concord's neighborhoods and wetlands, the air fills with the chittering calls of chimney swifts. These sickle-winged birds slice through the early summer sky in erratic arcs, their mouths open wide as they collect the season's bounty. The longest days of the year have arrived, and with them, the emergence of countless aquatic insects from streams, ponds, and marshes throughout the region.

Chimney swifts never land except to nest and roost. They feed, drink, and even mate on the wing. Their entire lives unfold in three dimensions above us. In early summer, these aerial hunters face their greatest challenge: feeding nestlings tucked inside chimneys and other vertical structures around town. The young birds demand constant provisioning, and parent swifts respond by hunting almost continuously from dawn until dusk.

The timing aligns perfectly with one of nature's most reliable food pulses. Mayflies, caddisflies, and other aquatic insects spend months or even years developing underwater as larvae. When water temperatures warm and daylight peaks, they emerge en masse over just a few days or weeks. The insects crawl from streams and ponds, shed their nymphal skins, and take to the air for their brief adult lives. Some mayflies live only hours as winged adults, just long enough to mate and lay eggs. For chimney swifts, this emergence represents a concentrated feast. The birds gather wherever the insects rise thickest. Over the Merrimack River and smaller waterways, swifts wheel and dive through clouds of newly emerged insects. Their gular pouches, expandable throat sacs, allow them to collect dozens of small insects during a single hunting flight before returning to feed their young.

The swifts hunt in layers. Some skim low over water surfaces where insects first take wing. Others patrol the middle air where thermal currents carry the insects higher. The highest fliers intercept insects that have dispersed widely from their emergence sites. This vertical partitioning means swifts can exploit the insect emergence at multiple elevations simultaneously. Parent birds make dozens of feeding trips each day. They compress their catch into a compact ball held in their throat pouch, delivering protein-rich meals to nestlings that will double their weight in just weeks. The young swifts must grow quickly. By late summer, they will join the adults in their remarkable migration to South America, spending the winter months in perpetual flight above the Amazon basin.

But for now, in these longest days, the focus narrows to the immediate demands of raising young. The adult swifts trace their hunting patterns against the evening sky, their calls echoing off buildings and trees. Each erratic flight path follows the invisible highways of rising insects, the ancient choreography of predator and prey played out in the air above Concord. Listen for their chittering calls overhead, sharp and insistent against the softer sounds of evening.