Perhaps the best known feature of Mission San Juan Capistrano, these birds by tradition arrive on St. Joseph's Day (March 19) each year and rebuild their mud nests around the eaves and elsewhere in preparation for breeding.  In actuality the return is more gradual, as the swallows migrate approximately 2,000 miles from winter homes in Central America and arrive over a period of several days or weeks.  After spending the spring and summer at the Mission, the swallows take flight once again on or about October 23 (the Day of San Juan).