Stressed Swallows

The recent chilly, damp weather in Colorado has curbed the activity of flying insects and has stressed those birds that feed on them.  Swallows are among our most abundant aerial insectivores and their behavior has clearly been altered by the prolonged cold spell.

In recent days I have watched large mixed flocks of barn, cliff, tree and violet-green swallows strafing ponds and meadows in the South Platte Valley, apparently snatching insects that hover near these relatively warm surfaces and gleaning sluggish prey from the grass or water.  The frenzy of activity might also flush insects from the dense vegetation, making them more accessible to the swallows.

One wonders how these birds consume enough prey on such chilly days to balance the energy expended to catch them.  When their aerial efforts prove to been inadequate, swallows are known to snare sluggish insects from bridges, river banks or the walls of barns and other outbuildings.  Nevertheless, the persistent, chilly upslope along the Colorado Front Range is surely stressing these agile hunters.