These Cliff Swallows were back and forth a few days ago, carrying mud for construction of their gourd-shaped nests tucked beneath the eves of a local barn. They carry one small chunk of mud per trip. Colonial nesters, many birds were busy that day. Cliff Swallows once nested on cliffs, and still will unless a barn or bridge or large culvert can be used. Man-made structures are the easiest place to look for them nowadays. You can see birds below, inside the completed gourd-shaped nests.