When I was taking an ornithology class some years ago (longer than I care to remember), we called them "dicky birds." Nowadays, we call them neotropical migrants. I am referring to a group of birds that live, breed, and nest in North America during spring and summer and migrate to and live in Mexico, Central America, South America, and the Caribbean Islands during the fall and winter. There are approximately 60 species of neotropical migrants that nest in Oklahoma (including the state bird the scissor-tailed flycatcher) and approximately 160 species that nest in the United States.
Despite many of these birds' being relatively common and often strikingly beautiful, many people are unaware that they exist. It is not uncommon for us to point out a painted bunting or a prothonotary warbler to a field trip group at the Noble Research Institute Wildlife Unit only to hear the response, "I never knew we had birds around here that look like that." I think that the lack of awareness can be attributed to several things, primarily that many neotropical migrants are small (house sparrow size and smaller). Unless a person really looks at them, it is easy to dismiss them as just a little bird. Their being here only part of the year also contributes to unfamiliarity with them, as does the fact that females often have drab coloration compared with that of males of the same species.
Neotropical migrants live in most habitat types, from prairie to forest. Some of the most productive sites to view them in are wooded riparian areas. These border creeks, streams, and rivers and often host numerous species.
There are several field guides that aid in identification. Some of the ones I am familiar with include A Field Guide to the Birds (Peterson Field Guide Series), Birds of North America (Golden Press), The Audubon Society Field Guide to North American Birds, and Field Guide to the Birds of North America (National Geographic Society).
So the next time you are out in the field or driving down a country road, and you see a UFO fly into the grass or trees, take a little extra time and try to get a good look at it. You might be rewarded by viewing some of nature's remarkable handiwork.