The Semipalmated Sandpiper, which winters in South America, reaches its subarctic breeding grounds mostly by using the Central and Eastern Flyways of North America. Its migratory paths include Washington State, although we see fewer of these birds than do other parts of the country. Sometimes they are seen here in northbound migration, but most frequently in southbound. Occasionally one is seen in the Edmonds marsh in spring but most sightings at the marsh or along the waterfront occur when these birds are returning to their South American wintering grounds. August is a prime month for spotting this sandpiper.
The first two photos show an adult and a juvenile bird earlier in August on a low tide, just north of the Brackett’s Landing jetty. They were among a small flock of Western Sandpipers, with which they are easily confused. Both species are about the same size, both have black legs and black bills. The Western Sandpiper sports more reddish plumage and has a longer bill slightly curved downward at the tip. If you get close enough to a mixed flock of both of these sandpipers, the Semipalmated Sandpiper most often has a noticeably shorter and straight bill. Sometimes the two species cannot be distinguished because of gradations in plumage color and in bill length. Semipalmated refers to the partial webbing between this sandpiper’s toes. It is very difficult to see in the field but can sometimes be captured in photos. You can see it on the right foot of the bird in the fourth photo.
As is the case with many shorebirds, during migration the Semipalmated Sandpiper can be found on mudflats in the intertidal zone, beaches, and shallow estuaries and inlets. Its diet is made up of tiny aquatic insects and crustaceans, but its diet varies with season and location. It eats mostly insects during breeding season, focusing on flies and their larvae but also eating some spiders, snails and seeds. During migration it forages on a variety of small crustaceans that live in shallow water or wet mud. It forages by walking on wet mud, looking for prey. It sometimes probes in mud with its bill. Along the coast it feeds mostly while the tide is ebbing or at low tide. It will also forage at night.
In breeding season, the male defends his territory with a display flight, fluttering his wings and singing a trill that has been described as sounding like a tiny outboard motor. His song attracts the female. The two courting adults may chase each other around the male’s territory. The nest site is on the ground, often on an island or at the top of a low mound, under a small bush. The nest is a shallow depression lined with moss, leaves, and grass. The male makes a number of potential nest scrapes and then the female chooses one and adds the nesting materials.
Both adults incubate the four eggs for about 20 days. Both parents tend the hatchlings for the first few days and then the female departs. The male remains with the young until they are old enough to fly. The young can make short flights at about two weeks and can fly fairly well at 16-19 days.
The Semipalmated Sandpiper migrates in large flocks and may make long nonstop flights between major feeding areas on its migration route. We do not see migration by large flocks of this species in Washington. On average, adults move south about a month before the juveniles. The oldest Semipalmated Sandpiper of record was 14 years and two months of age when recaptured during a banding operation in New Brunswick.
There are three breeding population of Semipalmated Sandpipers. They breed in Western Alaska, the Western Canadian Arctic and the Eastern Canadian Arctic. There are an estimated 2.26 million breeding birds. The eastern population appears to be declining but the breeding bird populations in Western Alaska and the Western Canadian Arctic appear to be stable. The species is on the 2014 State of the Birds Watch List because it is at risk of becoming threatened or endangered in the absence of conservation efforts.
The song of the male Semipalmated Sandpiper can be heard here: https://www.xeno-canto.org/424198.
— By Carol Riddell
Carol Riddell manages the bird education displays, on behalf of Pilchuck Audubon Society and Edmonds Parks & Recreation, at the Olympic Beach Visitor Station.