On this cool, sunny morning along the Colorado Front Range, we headed down to South Platte Park. In the course of our hike, the resident birds were, for the most part, neither diverse nor abundant. Red-winged blackbirds, yellow warblers, house wrens, robins, yellow-rumped warblers and brown cowbirds accounted for most of the birds in the trees and shrubs while only mallards and western grebes plied the lake waters.
An exception were the swallows, represented by tree, barn, cliff and violet-green species. Swooping above the reservoir, ponds and lakes in large, mixed flocks, they feasted on rising clouds of insects. While the tree swallows have graced the Park since late March, the barn and cliff swallows arrived in late April and the violet-green swallows, which will soon move into the foothills and mountains, have just recently returned from the south.
Those swallows not strafing the open waters gathered on power lines in large, linear flocks; seemingly obeying strict military protocol, one squadron would depart as another was arriving, assuring that the insects were subjected to a steady attack. As spring progresses, these social birds will become less gregarious though the cliff swallows will nest in colonies under bridges along the South Platte or on rock walls of foothill canyons; barn swallows, as their name implies, will seek out nest sites in a variety of human structures while tree and violet-green swallows will nest in tree cavities or bluebird boxes. By late summer, the massive flocks will reconvene, fueling up for the autumn migration.
