This morning, at Phillips Lake Park in Columbia, Missouri, my wife and I observed a large flock of cliff swallows building or repairing nests on the covered boat dock. The energetic birds repeatedly flew between a construction site and the dock, using mouthfuls of mud to construct their gourd-shaped nests; at least 100 were involved in the project.
Since they winter in southern South America, cliff swallows generally arrive in mid spring and produce nestlings by early summer, thereby insuring that they are ready for their "fall migration" by late August or early September. This morning's spectacle was thus unusually late, possibly resulting from a delayed spring arrival (due to our chilly, wet spring weather) or to a failed nesting attempt earlier in the season. Foul weather, disease or human interference may have played a role; since their large (sometimes massive) colonial nest sites can be a nuisance near human habitation (due to excrement, mites, noise, etc.) they are sometimes destroyed.
Regardless of the cause, this mid summer nesting frenzy what a sight to behold. No doubt, they will leave a mess behind when they finally head south but their vital role in natural insect control cannot be denied.
