Mating call recordings used to try to lure swallows back to Calif. mission Chris Carlson / AP This swallow veiwing area is used to watch nesting birds at the mission in San Juan Capistrano, Calif. By Gillian Flaccus, AP SAN JUAN CAPISTRANO, Calif. -- Reminders of the legend of the swallows are everywhere within the grounds of the historic Mission San Juan Capistrano: Tiny swallow silhouettes are etched into paving tiles, replicas of their distinctive mud nests hang from buildings and the gift shop overflows with swallow charms, figurines and postcards. What's missing are the swallows themselves. The graceful birds once swarmed to the 236-year-old mission each spring, flying from the pampas of southern Argentina to nest in the stone ruins of the mission's earthquake-damaged church. In recent years, however, the swallows have all but vanished after repairs meant removing some nests and urban sprawl crept closer to the mission's door. Now, decades after their annual ritual was immortalized in a chart-topping romantic ballad, the mission is attempting to lure the swallows back with a love song that's all their own. Speakers hidden amidst the colorful gardens play cliff swallow courtship calls for up to six hours a day during mating season in a last-ditch effort to woo the flocks back. The experiment, which began several weeks ago, is the brainchild of an Oklahoma ornithologist who has studied cliff swallows for nearly 30 years and has been consulting with the mission on how to win over the small, gregarious birds that have been intertwined with its history for at least a century. The story of the cliff swallows draws crowds each year for the annual month-long fiesta that marks their return and the Swallows Day Parade, with vibrant mariachi music, dancing and the ringing of the mission bells. They're ambassadors. If people only know to come to the mission because they hear about the birds first, and they arrive here and they have a sense of inspiration or they become better educated about California history ... then the birds have done us a service," said Mechelle Lawrence-Adams, the mission's executive director. Man-made nests hang in the eves at the mission in San Juan Capistrano, Calif. The tale of the swallows is almost as old as the mission itself. The historic landmark, founded in 1776, was the seventh of 21 outposts established by Franciscan missionaries in what is now California as Spanish colonizers pushed north and spread Christianity. The first missionaries noticed that each spring flocks of swallows would arrive in the area, usually around March 19, or St. Joseph's Day. In 1812, the mission's massive stone church crumbled in an earthquake and at some point, the swallows began nesting on the ruins of the towering stone chapel. The earliest written documentation of the swallow colony there is an article from 1915, but oral tradition indicates the birds were there years before that. In 1939, songwriter Leon Rene earned the cream-bellied birds a place in pop culture - and the nation's heart - with the love ballad "When the Swallows Come Back to Capistrano," which reached No. 4 on the charts and was recorded by numerous artists, including The Ink Spots, Pat Boone, Glenn Miller and Gene Autry. Suzi Patton, who visited the mission as a child, cherishes a memory of her mother standing in front of the mission bells and singing the song as dozens of curious swallows circled behind her, calling out as if in response. On a recent spring day, Patton stopped by with a friend for the first time in 40 years and was dismayed to find no traces of the birds. It's still a memory that's very vivid to me. I really loved it," said Patton, now 53. It's very different here now ... it's sad. What's Capistrano without the swallows? It's a problem the mission has been trying to address since the 1990s, when the swallows' nests came down during a project to retrofit and resurface the church ruins. In recent years, the mission has tried coaxing the birds back by affixing fake nests to the eaves of buildings, creating mud puddles to provide nest-building materials and sprinkling lady bugs, a favorite swallow food, on the ground. None of it has worked. Some swallows do return to the town of San Juan Capistrano each year, but instead nest in the eaves of downtown buildings, under freeway overpasses and in local creek beds. "If you went on your bike or took a trail walk in the summer nights," said Lawrence-Adams, "you'd see them all in the local creek beds and you want to yell at them, 'Go back to the mission! Go back!' The removal of the nests likely precipitated a regional population decline that was already underway, said Charles Brown, the cliff swallow expert consulting with the mission. Southern California has seen a steep decline in its cliff swallow population because of changes in the landscape, he said. Cliff swallows prefer flat, open spaces but urban sprawl has meant more trees planted by the region's booming human population. Say 100 years ago, when the birds were at their heyday at the mission, the landscape was much more open. If you look at old photos, it was basically out in the middle of a prairie, it was very open," said Brown, a professor at the University of Tulsa. Now, it's not very suitable for cliff swallows anymore and there are consequences when the landscape changes so much. Still, the mission and Brown hope their new strategy will pay off with a little patience. Staff members have reported seeing curious swallows flitting around the statue of Father Serra that obscures the broadcasting equipment and dipping and weaving over the gardens. There have also been plenty of false sightings. If they colonize, it will be very obvious what they are. Now people are seeing mockingbirds and house finches around there, but if they're landing in the trees and perching in obvious places, they won't be cliff swallows," Brown said. If there's nothing by mid-May, then it's probably not going to work this year - but that doesn't mean that it won't work next year.