This summer, a massive flock of cliff swallows has colonized a bridge over the South Platte River near downtown Littleton. Their gourd-shaped nest cavities, formed with mud, line both sides of the bridge and are four rows wide in some areas. Grass is used to coat the interior of the gourds, making them more comfortable for the nestlings.
This morning, the attentive parents were ingesting a variety of flying insects above the river and over the adjacent fields; indeed, I have seen flocks of them above our Littleton farm, almost a mile from the bridge. Exhausted parents temporarily rested on power lines along the river before resuming their sorties.
Long distance migrants, cliff swallows winter in southern South America, returning to North America to nest by mid spring. While most common in the western half of the U.S., their range has been expanding eastward as their nest site preference has shifted from cliffs to bridges and other human structures.
