In autumn a migration of swifts fly through Portland. Every night for two weeks, thousands and thousands of swifts funnel around the huge chimney of a local elementary school at sunset before diving in. It's one of the most amazing things I've ever witnessed. Often a hawk circles around the flock of swifts, darting between them until finally grabbing one and making a break for it. I was reminded of this when watching a smaller pair of birds attack this hawk protecting their nest.