Peregrine falcons hunt warblers in migration

The air above the Huron River carries a tension that wasn't here a week ago. Lilacs finish their bloom along the banks, their heavy sweetness mixing with the green smell of new leaves. But something faster cuts through this settled spring air.

A peregrine falcon sits motionless on the water tower, scanning the canopy below. The bird is sleek and compact, built for speed in a way that makes every other raptor look clumsy. Its dark head turns in small increments, tracking movement sixty feet down where bay-breasted warblers work through the maples. These small songbirds have been flying north for days, following the insect emergence that comes with warming weather. They move through the trees in loose groups, gleaning aphids and caterpillars from the newly expanded leaves. The warblers are tired from their night flight, focused on feeding, and predictable in their movements through the mid-canopy. The falcon knows this.

Peregrine falcons nearly disappeared from Michigan forty years ago, poisoned by DDT that thinned their eggshells past the point where chicks could survive. The population collapsed to nothing before the pesticide was banned and captive breeding programs began releasing young birds back into the wild. Now they nest on bridges and tall buildings throughout the region, their numbers recovered enough that seeing one hunt along the river is no longer remarkable. But what they hunt has changed. Before pesticides, peregrines fed mostly on shorebirds and waterfowl over open water. Now they take advantage of the spring migration bottleneck, when thousands of small songbirds move through narrow corridors of remaining forest. The warblers that pour through Ann Arbor each May represent a concentrated food source that wasn't available to falcons a century ago, when continuous forest spread across the region. Migration routes have compressed into fragments, and falcons have learned to position themselves along these aerial highways.

The strike happens faster than the eye can follow. The falcon drops from its perch and accelerates into a shallow dive, reaching speeds that would tear apart a less perfectly designed bird. It doesn't stoop straight down like it would over open water, but angles through the canopy gaps with surgical precision. A bay-breasted warbler, focused on a cluster of emerging moths, has no time to react. The impact is silent from this distance, over in an instant. The falcon carries its prey to a horizontal branch and begins feeding while the other warblers continue their search through the leaves, already resuming the rhythm that migration demands. Yellow-throated warblers work the oak bark nearby, their longer bills probing for insects the bay-breasted birds cannot reach. They seem unaware that one of their traveling companions has just been removed from the journey.

The water below reflects the full canopy now, solid green broken by patches of sky. Listen for the sharp kek-kek-kek call that announces a falcon's presence, or watch for the sudden stillness that falls over the smaller birds when a predator appears overhead. The hunt continues in the space between the flowering trees and the water, where speed meets the slow patience of migration.