Barn swallows and the insects of late spring

The air above Stanley Park carries a different weight this morning. Barn swallows (Hirundo rustica) slice through it in sharp turns, their wings catching light as they bank and dive. Each pass through the warming air brings insects into their mouths. The swallows have been back for weeks now, but their hunting has changed. Where they once flew leisurely loops to rebuild strength after migration, they now fly with purpose.

These threatened birds time their breeding to match the emergence of flying insects from Vancouver's wetlands and forests. Midges rise from the surface of Beaver Lake in soft clouds, their brief adult lives measured in hours. Crane flies unfold from the damp soil beneath the cedars. Small moths flutter up from the understory as the day warms. The swallows read this emergence like a calendar. Their mud nests, tucked under the eaves of park buildings, now hold eggs or newly hatched young that demand constant feeding.

A barn swallow catches insects at the rate of one every few seconds during peak hunting. The parent birds alternate trips, one staying with the nest while the other works the air above the lake and meadows. They target different insects at different times of day. Morning brings the emergence of aquatic midges, their synchronized hatching triggered by water temperature and light. Afternoon thermals lift beetles and flying ants from the forest floor. Evening calls up the caddisflies and small moths. Each insect species follows its own rhythm, but together they create the abundance that barn swallow reproduction requires. The timing must align. Too early, and there are not enough insects to feed growing nestlings. Too late, and the young will not be strong enough for the long flight south.

The swallows' flight patterns trace these invisible insect highways in the air. They work the edges where forest meets open water, where warm air rises from sun-heated surfaces, where insects concentrate. Watch one bird for a minute and you begin to see the aerial landscape it reads. A sudden climb means insects caught in an updraft. A series of tight turns marks a swarm too dense to pass through. The bird's tail spreads and closes like a rudder, adjusting its path through air thick with prey. Each successful hunt means another few grams of protein delivered to the nest, another day closer to fledging young that will join the hunt themselves. The morning air holds both the insects and their hunters, each following patterns older than the city that now surrounds this green space.