Take a stroll on a sandy beach just about anywhere in the world, between December and March,

and there's a chance you'll meet a plump little shorebird called the Sanderling.

Scurrying back and forth across the beach in small flocks, sanderlings forage for

tiny crustaceans and mollusks in the wet sand.

These are those endearing little birds you've seen running up the beach just ahead of an incoming wave.

They look like they're trying frantically to keep their sneakers dry.

But when the wave recedes, the sanderlings turn around and chase after it.

They peck and probe, snatching up invertebrates they find stranded in the sand.

After a hearty meal and some digestion, a sanderling will often hack up a pellet made of sand and bristling with bits of exoskeleton and shells.

Sandalings are a species of sandpiper, one of the most familiar sandpipers, actually,

because of their vast distribution across the world's coastlines.

In the non-breeding season, which is usually when we see them on beaches,

sandalings wear a plumage of pale gray and white.

They have black bills and black legs. They use those little legs to run at

impressive speeds across the beach. One Spanish name for the species is Correlimus tridactilo,

which means three-toed runner. Most of them hang out in flocks at this time of year, but here and there a sanderling will get all territorial and decide that it owns a particular patch of wave-washed beach.

It will vigorously chase off any other sandalings that wander into its territory.

The territory owner hunches its shoulders, throws its head forward, and runs full force at the intruder.

A chase ensues with a blur of tiny black legs. The intruder might stop and turn around and act

tough for a moment or two, but in the end they always back down. Like most other sandpipers,

sandalings migrate far to the north in summer.

They breed on the high Arctic tundra, mostly in Canada, Greenland, and Siberia.

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