Cliff Swallow

Cliff Swallows nest in colonies, with adobe-like nests often touching each other. Avian architects, their individual nests looks like a gourd, with a small hole serving as the entrance. Cliff Swallows (the "Swallows of Capistrano") often nest below eaves, the mud plastering the nest from behind and above. Photo: KSchneider (CC BY-NC 2.0)