We often see Northern Harriers flying not far above the edge of the bay, distinctive for their relatively low height as they cruise above ground, the V-shaped posture they hold as they fly, and the visible white rump (when seen from the right direction). I often see them above the dunes near the ocean's beach.
Last fall I was fortunate to find one standing on a post at the edge of our wetland on Willapa Bay. I slowly approached with my camera, keeping my distance and enjoying the full view of the bird while staying relatively still. I was able to get several shots, including this one (left) with the spreading tail, clearly showing the white rump patch.
Another very distinctive feature of the Northern Harriers is their owl-like facial outline of lighter feathers (visible in all of the fence-sitting photos).