Birds are very active, so observation time can be brief. In order to look up the bird later in a field guide, the observer must try to quickly note features while the bird is in view. Wing bars, eye-lines and eye-rings, breast markings, tail spots, and bill and leg color can usually separate even very similar birds.
Eye-ring or eye-line. Determining whether the bird has an eye-ring or eye-line can help distinguish a Bell's vireo from a red-eyed vireo.
Plain wing or wing bar. Focus on the wing and determine if the bird has a plain wing or wing bar to distinguish an Eastern phoebe from an Eastern wood-pewee.
Breast spots or breast streaks. Distinguishing between breast spots and breast streaks can help distinguish a wood thrush from a brown thrasher.
Every bird species exhibits its own identification clues, including size and shape, color and field marks, songs and calls, behavior traits, and habitats where they are most likely to be found. Some species can be identified from just a few clues, while others require careful observation of every detail and trait.
How big is a certain bird compared to one you already know, such as a house sparrow, a robin, or a crow?
Is the shape of the bird slender like a mockingbird, or chunky like a meadowlark?
Is the bill cone-shaped like a cardinal's, fine as a warbler's, or thicker like a vireo's?
Are the wings shaped like those of a Forster's tern, a Northern bobwhite, or a red-tailed hawk?
Is the tail deeply forked like that of a barn swallow, slightly forked like an Eastern bluebird, or rounded like a blue jay?
Does the bird cock its tail up like a wren or flick its tail like an Eastern phoebe?
One of the clues to identifying birds is to know what to expect seasonally. For example, the chipping sparrow and the American tree sparrow look similar. Both have wing bars, eye-lines and plain breasts. The chipping sparrow, however, is a summer resident while the American tree sparrow occurs in Missouri only in winter.
Each species of bird is associated with a particular habitat or habitats. Habitats usually have certain vegetative or landform characteristics that provide the species food and shelter. Knowing the habitat associations of a species enables you to know where to look for it. Generally, the more habitats you visit, the more kinds of birds you will see. An understanding of habitat associations also will enable you to know what to expect where, and can, therefore, be used to identify birds.
For example, although the upland sandpiper and greater yellowlegs are somewhat similar in appearance, the upland sandpiper is found on grasslands, while the yellowlegs is usually found along shorelines when in Missouri.