Each year on St. Joseph's Day — March 19 — the famous bells of Mission San Juan Capistrano ring out to announce the return of the cliff swallows. These migratory birds leave each year on St. John's Day — October 23 — to spend their winters in Goya, Argentina, but they make the 6,000-mile return trip to Southern California each spring when the weather turns warm again.

The cliff swallow, whose scientific name is Petrochelidon pyrrhonota, is a member of the Hirundinidae bird family and is related to the martin. On average, cliff swallows are five inches long and have tiny bills.

Adults sport a blue back and crown with brown wings and tail. Their bellies are white, and their faces are red with a white forehead.

Cliff swallows exist mainly on a diet of insects that they catch in flight. They breed in large colonies and build cone-shaped nests made of mud, in which they lay three to six eggs on average.

Their name comes from the fact that they like to make their nests on cliffs, although modern development has led them to prefer the eaves of a variety of man-made structures.

Legend has it that the cliff swallows have returned to San Juan Capistrano every spring for centuries — ever since they first took refuge at the mission when an angry innkeeper destroyed their mud nests.

Scientists believe the mission's location near two rivers make it an ideal location for the swallows to nest. There is a good supply of the insects they like to eat and the ruins of the old stone church offer protection.

The residents of San Juan Capistrano look forward to the swallows' return every year. Bird-watchers keep an eye out for “scout swallows," which precede the main flock by a few days.

The town hosts a week-long festival, the Fiesta de las Golondrinas, which celebrates the birds and ends with the Swallows Day Parade and Mercado Street Fair.

Unfortunately, fewer and fewer swallows seem to be returning to San Juan Capistrano in recent years. Scientists believe this could be due to many of their nests being destroyed during recent renovation work on the mission.

Others think continued development in the area has reduced access to insects they rely on for food. The swallows that do return to the area can now often be found under the eaves of nearby colleges and shopping malls, as well as the spaces underneath interstate overpasses.

Wonder What's Next?

Spring forward with us tomorrow, as we explore the science behind the changing of the seasons Wonderopolis-style!