Pamelia and I were eating dinner on the deck at our house last evening while a variety of birds ate dinner above us. Among them were some unusual gulls, some terns that we weren't used to seeing at this spot, and some gull-sized birds with distinctive white stripes on the underside of their wings. These latter birds were darting and swooping like swallows. They were snatching insects out of the air.
After consulting a couple of birding books, we recognized the striped-wing birds as nighthawks. We don't see them here regularly, but they are passing through as they migrate to South America. Pamelia and I are preparing to go to California in a few weeks to do a magazine story on Western bird migration, so our migratory radar is up. Yesterday morning had a flock of mergansers, who haven't been here since spring.
Depending on where you live, you might want to check the trees and the skies over the next month for birds you don't usually see. Look on the Internet for a birding site specific to your state or country. Some sites even show update maps of where migrating birds are at the moment.