At the State Park the other day, I amazed and delighted a group of toddlers by pointing out the cliff swallow nests under the eaves of the restrooms.

The cliff swallow is among North America’s most social landbirds. They often nest in large colonies, with a single site sometimes hosting several thousand active nests. Their nests are made from sticky clay, which can endure for years, and the birds’ tier-stacking building technique helps support them. Swallows from the same colony cooperate in nest building: they gather mud together in small areas and then return to their nests carrying clumps in their bills. They preen, feed, drink, and bathe in groups, and they continue sticking together in large flocks during migration and on their wintering grounds.