Wednesday will be a big day in a little town located between Los Angeles and San Diego, California. It's the day that a great flock of swallows will return to the site of the old Spanish mission at San Juan Capistrano, just as the birds always seem to do precisely on March 19th. There's even a famous song about it. It was a hit in the big-band era of the 1950s:

When the swallows come back to Capistrano,
That's the day you promised to come back to me.

Legend has it that each Saint Joseph's Day, March 19th, swallows that have migrated 9700 kilometers from Goya, Argentina, reappear en masse in Capistrano. And then, as the song says,

All the mission bells will ring.
The chapel choir will sing.

The reality is that the birds straggle in over several days in mid-March. Their exact arrival dates depend upon weather conditions between South America and California. But there are almost always enough birds on hand for the mission to throw a celebration party, which it does every March 19th.

Along with bird-watching, visitors tour the historic mission, which Franciscan priests and Spanish settlers built in 1776, the very year that a new nation called the United States was born on the eastern side of the continent.

The mission was one of several along a crude California road that became known as El Camino Real ? the Royal Road. Throughout California, you still see the symbol of that road ? an old mission bell hanging from a curved pole ? though it's often hard to spot the bells among California's modern freeways, subdivisions, and shopping centers.

Five hundred thousand visitors, including 80,000 schoolchildren, tour San Juan Capistrano each year. This week, as huge crowds jam the mission grounds, and as all heads turn skyward, it can seem as though all 500,000 visitors have come at the same time, hoping to witness the spectacle of the swallows' return.