Birdwatchers can identify birds either at home or in the field using online or printed field guides. These field guides help birdwatchers identify a bird by comparing the observed shape, size, color and behavior of the bird with the kinds of birds known to be in the area.
To use the field guide, bird-watchers compare the silhouette of the bird to other common silhouettes. The silhouette contains information about the size, proportion and posture that can rule out many birds. Bird-watchers further eliminate birds by comparing the size and shape of individual parts of the anatomy, both alone and in relation to other parts of the bird.
They can also focus on the overall color pattern of the bird. Wear and tear on the feathers can affect colors, but the overall pattern is still present. Stripes, edgings and marks in distinct locations help to differentiate species. If two species have similar patterns, they can often be distinguished by how bold or faint the markings appear. Some birds have distinctive colors, making them easy to identify by color alone.
A bird's posture, movement, flight pattern and feeding style can all provide valuable information for identification. Bird-watchers observe the bird for as long as possible to observe as many of these behaviors as possible.
The habitat of the bird should be noted. Birds are choosy about their environment, preferring some areas over others. The location of the bird is important to narrow down the species.