To identify a bird based on its silhouette while flying, compare its size and shape to birds you know well to narrow down the species, then look it up in a field guide. Studying the guide ahead of time can help you correctly identify birds.
Silhouettes can provide valuable clues to a bird's identity. The shape of the beak is often apparent and can identify what the bird eats, which can narrow down the bird's species. A broad, flat beak may indicate the bird catches insects, while a curved beak can be used for a digging. Birds of prey like hawks and owls often have short, hooked beaks used for grabbing and tearing apart prey.
Once the general type of bird is determined, the shape of the body and wings can help narrow down the species. For example, when comparing birds of prey, a falcon has flatter wings than an osprey, which has a notable crook at the wrists to create an M-shaped silhouette. Birds that fly quickly or rely on diving through the air to catch prey have more streamlined bodies, while waterfowl often have fatter bodies and longer necks.
Size can be a useful factor in identifying a bird but may be difficult to assess when a bird is in flight and can confuse an amateur birdwatcher. Try to wait until the bird passes by an identifiable landmark to get a better idea of its size.