San Juan Capistrano and Return of the Swallows 

Swallows are small birds that build mud nests on the sides of buildings under eaves and other places where they find protection. The Mission San Juan Capistrano is one such place the swallows like for their rites of spring--building nests to lay eggs and hatch them.
Each year scout swallows precede the main flock by a few days and begin the work of building mud nests that cling to the ruins of the old stone church of San Juan Capistrano. The arches of the two story, high vaulted Chapel were left bare and exposed, as the roof collapsed during the earthquake of 1812.