In 1980, biologist Francisco Delgado, a Chitré native who studied in Leningrad, in the former Soviet Union, began coming out to the beach at low tide to band the legs of western sandpipers (Calidris mauri), a palm-sized, rather nondescript gray shorebird with long legs and beak.

He and his assistants band 30 birds a day; early risers can often spot the researchers wading out in the shallow waters. Next to the beach is the ecological station he runs, Estación Ecológica Alejandro von Humboldt, housed in a modest cinderblock building. Driving toward Playa El Agallito, it’s on the left as the road ends.

The western sandpiper’s home turf and breeding ground is western Alaska and northeastern Siberia. There are an estimated 3.6 million western sandpipers, which makes them the most populous shorebird along the Pacific coast of North America.

In the fall, they begin their southern migration. It’s an amazing journey. The little birds can fly 20 days without a stopover of more than a few hours in a few key spots, including British Columbia (Canada) and the San Francisco Bay. And they travel enormous distances: These Arctic dwellers have been found as far south as Chile.

An unbelievable number make their way to Panama’s Pacific coast, where they spend the winter or just stop briefly on their way to South America: Bird-watchers have been stunned to watch throngs of literally hundreds of thousands of them at a time, especially around eastern Panama Bay.

Many of them, not surprisingly, like to spend the winter in Panama. What’s more surprising is something else researchers are finding out about their migrations. To say they’re creatures of habit is putting it mildly: Year after year, the birds come back to the same spot.

This is true on the larger scale — western sandpipers that winter in Panama, for instance, always go to Panama; those that winter in Peru always go to Peru. But Delgado has found that the same holds true on a very much smaller scale. The same birds don’t just come back to Playa El Agallito each year; they come back to the same part of the beach. If they’re chased away by a predator such as a falcon, they’ll return in a few minutes. Delgado has tracked two birds that have come back to the exact same spot for 10 years.

One theory of why the birds are so wedded to such a seemingly rigid migration pattern is that, because their grueling transcontinental trip requires enormous stores of energy, once they touch down they need to replenish themselves urgently. Those that survive a migration have learned where food is plentiful and safe and stick with the same location year after year. If their normal stopover points and wintering grounds are damaged or destroyed, the loss could be fatal for whole populations of the little birds.

There is considerable evidence this is happening. The global population of western sandpipers dropped dramatically in the 1990s. A good part of this is likely attributable to the El Niño phenomenon. But pollution and habitat destruction are believed to play significant roles as well.

Delgado estimates that 10,000 western sandpipers come to Playa El Agallito each year, in flocks that average 300. They start showing up in late October and leave in early March. Delgado worries what will happen to them if their habitat is destroyed.

This has already happened to some extent. While the area still has mangrove forests, large tracts have been hacked away. Recently, for instance, environmentalists lost a battle with commercial interests that went on to destroy mangroves and flood shallow salt ponds to create a 600-hectare shrimp farm.

The ponds are now too deep for the sandpipers to roost or hunt for food, and the population that wintered there, who knows for how many years, has been scattered. As usual when it’s sandpipers against humans, the sandpipers didn’t stand a chance.

“Money is money,” Delgado says.

Money is not something Delgado and his team have much of. He doesn’t even have enough to patch the tattered net he uses to trap birds for banding.

Those interested in helping Delgado or learning more about his work can email him (delgadofrancisco2410 [at] yahoo [dot] com) or call him in Chitré (tel. 996-1725).