The western sandpiper is a small little shorebird that you can spot along the coasts of North America. Individually, they are modest in size — however, a western sandpiper flock is not easy to overlook.

These communities can grow to a collective number in the hundreds of thousands. The largest gatherings are typically at San Francisco Bay and the Copper River Delta in Alaska.

It’s estimated that just about the entire breeding population passes through the Copper River Delta. But this takes place for only a few short weeks each spring. Once breeding is over, the birds migrate south to feed along the lakes, marshes, and ponds along the Pacific coast.

Before making their arduous quest north, western sandpipers must exercise their wings. The entire extravaganza is mesmerising. A single, organised group shoots up towards the sky, flipping and turning in perfect unison. Creating a flashing illusion as they rotate their bodies simultaneously to display their white underbellies — then their dark backs.

This demonstration is known as murmuration. You may have seen this with other bird species before — it’s quite common for starlings.

As the seasons change, so do western sandpiper plumes. In fact, this bird goes through an entire 5-phase molting process every year. Molting is an exchange of feathers — out with the old, in with the new. The process has two functions: replace worn feathers regularly and reflect the birds’ age, sex, and season.

A few features are shared amongst western sandpipers, regardless of age or sex. They all have thin black legs with webbed toes, a narrow black beak, and a white underbelly. And during winter, the entire flock sports a pale grey back. If you look closely, though, female sandpipers have slightly longer bills than males. During breeding, adults develop brown and rufous (red) feathers which sprinkle their crowns and backs.

While enjoying their Alaskan “bird-cation”, western sandpipers waste no time. They form their breeding grounds under vegetation. The males will forage several small divots in the earth, lined with lichens, leaves, and grass. He then displays these to the female — she’ll choose the best one and then lays her eggs here.

Both parents participate in incubation. Their teamwork continues once the eggs hatch as the parents work together in caring for their young. Males are particularly protective of their families — they guard not only their nesting sites but also their mates. The birds are monogamous, and the males make every effort to ward off intruders. Even in flight, the male will usually follow his mate.

In their California habitats, western sandpipers forage the ground for small invertebrates, crustaceans, and sometimes biofilm. They catch their prey by probing mud and sand using their long, pointed beeks.

At about 16 cm long, weighing no more than 35 grams, western sandpipers are San Francisco bay’s smallest sandpipers. In an effort to protect, restore, and enhance this habitat, San Francisco Bay Restoration Authority created a fund — the Measure AA parcel tax. And in Central Valley, they have partnered with other NGOs and rice farmers to improve shorebird habitats on working lands.