Behavioral traits that aid in bird identification are posture, movement, flight pattern, feeding habits and flocking. Consult a good print or online field guide that describes at least some of these traits alongside each entry, such as the online bird guide of the Cornell Lab of Ornithology.
Birds posture themselves in different ways according to species, and two species as similar looking as the Acadian flycatcher and pine warbler are sometimes best distinguished by posture. The Acadian flycatcher has a vertical posture, whereas the pine warbler often crouches itself in a more horizontal position. Movement is also key. Many species of sparrows hop on the ground, whereas many shore birds walk. Movement is especially important when distinguishing ducks, as North American ducks are usually placed in two groups based on whether they dive for their food or merely tip their front end into the water.
Flight patterns vary from the lengthy soaring of some raptors to the constant flapping of certain sparrows. Birds also eat in different ways, some on the run, some while hopping on the ground, some while perched and others while swimming. As some species of birds tend to form flocks, the presence of many individuals flying and feeding together can eliminate solitary species from the identification process.