Invasion of Violet-Green Swallows

On this cool, cloudy morning along the Colorado Front Range, large flocks of violet-green swallows swirled above the South Platte, strafing the river and adjacent ponds for insects.  Just as many perched on nearby power lines, resting in the chilly drizzle.

Having wintered in Mexico or Central America, these aerialists usually arrive in late April or May, resting and feeding on the Piedmont before heading into the foothills and mountains.  There they will nest in tree cavities or rock crevices and feast on a variety of flying insects.  Throughout the summer, they are often observed in foothill canyons, feeding with white-throated swifts.

Damp, chilly conditions force swallows to congregate along and above rivers or lakes, where their prey hovers over the relatively warm water.  I encountered about 850 violet-green swallows along a 1.5 mile stretch of the river this morning, joined by much smaller numbers of cliff, barn, tree and rough-winged swallows which arrived earlier and have already dispersed along the Front Range.