Those beautiful tail feathers belong to a young Cooper’s Hawk. The photos are from Vlad Oustimovitch, who explains:
The Urban Raptor Conservancy has been banding Cooper’s Hawks as part of a study for several years. This juvenile male was banded this morning by Jake, a volunteer from the conservancy. It is one of four offspring from a nest next to our Gatewood property in the Orchard Street Ravine.
The URC explains that ongoing study here, saying that Seattle is one of several major cities where Cooper’s Hawks are studied, after they began expanding their range into urban areas a quarter-century ago. The URC summarizes, “Since 2012, the number of nesting pairs has increased each year, with high nest success rates, high fledgling productivity, little evidence of migration, strong site fidelity, and mostly short post-fledging dispersal distances.” Last year they documented “46 nesting attempts, 40 successful nests, and 145 fledglings” in Seattle; the year’s full report is here (including some West Seattle photos).