This species, common in winter in the Bay Area, breeds in the far north, where most of them have gone by June. This one shows partial molt, with about half old and half new feathers on back and wings. Bill Bousman suggested that it might be a year-old (SY) bird, without enough new plumage to make the long migration and/or nest successfully. Query: do we regularly see SY Greater Yellowlegs summering here?