A flock of sandpipers foraging on the mud looks at first like multiple copies of the identical bird. And some flocks undoubtedly fit that description. But this particular flock, on closer inspection, consisted of at least three different species. Most were Western Sandpipers (Calidris mauri). At least a dozen Dunlin (Calidris alpina) joined the flock, together with about as many Semipalmated Plover (Charadrius semipalmatus).
The Western Sandpipers do their breeding in the coastal tundra regions of western Alaska and eastern Siberia. They spend the winters mostly along the Pacific Coast from British Columbia down to Peru. What we’re seeing here is a relatively tiny flock of them; they’ve sometimes been seen in huge numbers. They’re here on a rest and refueling stop on their northward migration to their breeding grounds. They have narrow webs between their toes but have somehow avoided the “semipalmated” label. All the Western Sandpipers in this flock were wearing their breeding plumage. In winter they are a dull grey or grey/brown. Now the feathers on their outer wings have dark accents and reddish margins, and the top of the head is heavy with rust and a dark streak. A light eyebrow stripe remains. There are dark flecks on the throat and to some extent down the breast and belly. They routinely fly about 200 miles per day, but can do much longer, up to 1150 miles per day. The one above is probably a male, based on its relatively short straight bill. Females are a bit bigger and their bill is longer with a downward bend at the very tip. The small photo at the right may be a female. There is some sex segregation in their migration, with more than twice as many males as females spending winters in California. Males arrive first in the breeding areas and establish territories. Females pick who they like. The nest is a hollow scraped in the ground, lined with leaves. Once paired, they are monogamous rarely coupling with others. Both sexes brood the eggs and feed the hatchlings, but females take off before the chicks can fly, leaving males in charge. Next season each may choose a different mate.
The Dunlin used to be called the Red-backed Sandpiper, based on its breeding plumage, which it displays here. The black belly is a key part of its breeding plumage that makes identification easy at this time of year. It breeds in much the same sub-Arctic Alaskan regions as the Western Sandpiper, but has a much larger breeding range extending literally around the world near the top of the globe. Unlike the Western Sandpiper, it prefers wet or boggy habitat for nesting, and always wants to be near water. They don’t migrate as far as the Western Sandpiper; the populations we see here probably did not go further south than Baja California. On the trip south they’ve been known to fly 2100 miles nonstop from Alaska to California in 72 hours, an average speed of 29 mph. On the return trip they usually hit a rest stop after 500 miles. The nest, like the Western Sandpiper, is a scrape in the ground lined with leaves and grass; the male does this. Like the Western Sandpiper, they’re monogamous for the season. The eggs can survive spells of cold. One clutch of eggs was covered with snow for 16 hours but after parents returned and brooded, all the eggs hatched.
The first time I saw this striking-looking bird, it foraged separately from a nearby sandpiper flock, as if it were here on its own. This time, this bird came mixed in with the Western Sandpipers and the Dunlin, making no effort to get away by itself. I had to wonder about its feeding method. The sandpipers and Dunlin used the rapid-fire random pecking method (like a sewing machine) that probably came up empty 90 percent of the time, but ten percent would yield a good enough diet. The plover did not speed-peck. It scooted from place to place, pecking only occasionally. I couldn’t tell whether its pecks were successful. I wrote more about this bird yesterday (“Semi What?” May 3 2022) so go check it out there.
There may also have been other species in this flock that I missed. If you see any in the video above, please let me know.