Tuesday, May 23, 2017

Sanderlings: Arctic Swashbucklers

Sanderlings (Calidris alba) are smallish sandpipers of the swash zone, perhaps the "peeps" seen most commonly on the beaches of central California.  They stick together in flocks as they run up and down the beach, chasing the waves as they forage in the swash zone.  (The swash zone is the part of the beach that is covered with each incoming wave, and uncovered again to reveal potential tasty morsels beneath the sand.)

The rather cute, gentle appearance of Sanderlings belies their amazing life strategy.  These birds may not look it, but they are truly daring, swashbuckling adventurers, flying thousands of miles between overwintering grounds around the world and breeding grounds high above the Arctic Circle. 

Sanderlings are one of the most widespread shorebirds in the world, found during the winter on most temperate and tropical beaches.  For most of the year, they can be found in California, though numbers are lowest in June when they return to the Arctic to breed.  A few nonbreeding adults may stay behind during the summer, saving themselves the energy required to migrate. 

After incredible long-distance migrations, Sanderlings breed on the tundra far above the Arctic Circle.  They nest on dry tundra with low growing plants, such as lichens and mosses, building nests on the ground.  These nests are little more than shallow scrapes, perhaps lined with small leaves.

A favorite food of Sanderlings is sand crab (Emerita analoga), thumb-sized crustaceans that spend most of their time buried in the sand.  Sanderlings also eat other invertebrates, such as amphipods (shrimplike crustaceans with laterally compressed bodies, sometimes called beach fleas or sand hoppers) and isopods ("pillbug"-like crustaceans with dorso-ventrally compressed, or flattened, bodies), as well as marine worms and small mollusks. 

Aside: If you happen to be interested in the dazzling array of invertebrates that inhabit California's enchanting coastline, I highly recommend Ed Ricketts' classic book, Between Pacific Tides.  It has yet to be surpassed in breadth and depth in the nearly 80 years since its original publication in 1939, and I find it to be very readable and enlightening.

Sanderlings in May, beginning to show colorful breeding plumage

Sanderlings are pale most of the year, gray above with extensive pure white on chest and bellies.  Most commonly, this is how we see them during the winter months in California.  During the summer breeding season, Sanderlings' backs and heads become flecked or spangled with black, white and red.  The birds we saw at Moss Landing recently, during the second week in May, were beginning to show their brighter breeding plumage (see photo above).

Sanderling in March, much paler in color as they appear through the winter.
Though this is a common and widespread species, its future is not considered entirely certain.  According to Cornell's All About Birds website, between 1959 and 1988, the number of Sanderlings in California decreased by 3.7% each year.  This decrease is likely due to development of shoreline habitat as well as exposure to toxins.  Pesticide runoff from nearby agricultural fields, oil spills, municipal runoff (chemicals, oils, etc. from cities' storm drains) and ever-increasing plastic pollution on our beaches and in our oceans pose very real threats to shorebirds and the greater ecosystem.  Overwintering habitat is critical for migrant shorebirds like Sanderlings, and in California much of that habitat is protected by California's State Beaches.

Next time you visit the beach, pay special attention to the small shorebirds chasing the waves in the swash zone.  Learning to identify Sanderlings is the first step in decoding the sometimes mystifying group of sandpipers and other shorebirds.

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