In fact, southbound migratory shorebirds have been back in the Pacific Northwest since the last week of June, but it is timely to write about them, as they are probably at their peak at the beginning of September.
The adults come back as soon as their young fledge, but of course some nests fail, and those adults are the first to return. Why stay in the Arctic, with all those mosquitoes and arctic foxes, when where you really should be is on a mud flat in Grays Harbor or a sandy beach in Sinaloa? Some of them are going farther, well into South America, so they had better get an early start for that long flight.
Perhaps because they are big enough to potentially ward off predators, large shorebirds such as curlews and godwits divide parental responsibility, and the sexes migrate together. This is also true of most plovers. But the first Western Sandpipers you see in fall are probably those that failed at nesting, then a large wave of females that have left their families, then the males.
Many of these species undergo body molt while they are migrating, so in the fall we see birds in breeding plumage, in nonbreeding plumage, and at all stages in between. In addition, another plumage complicates the issue. These are the juveniles, young of the year that migrate after the adults. The peaks of their migration are often about a month apart, so in some species that continue south after passing through our region, we see a lot of adults and then a lot of juveniles, but not much mixing.
When trying to identify unknown shorebirds, it is extremely important to place them in a plumage, or at least an age stage. In fall, the adults have very worn body feathers until they are all replaced, and many of them don’t replace all their feathers until some time in the winter. Of the flight feathers, both the primaries and the tertials (the feathers of the inner wing that cover the primaries when the wing is folded) become very worn, and that wear is easily seen. Juveniles, on the other hand, have neat unworn feathers, including the primaries and tertials.
Get out to the coast and savor the shorebirds. You can easily see one to two dozen species on a good day, and identification is much facilitated because they are often in mixed-species flocks.