There are four main traits about bird that will help you to quickly determine which group a particular bird species belongs to. With some species, it is possible to use just one of these features to arrive at a successful identification. For example, duck species can often be easily identified by just the head and wing color of the males. However, to identify the females of these same species, you must look at several characteristics.
Some of the main characteristics that are useful in identifying a bird are discussed below.
Plumage
Plumage is often the most important trait used in successful bird identification. Most bird species have a distinct plumage color and pattern which can be used to distinguish them from all other species. However, there are some groups of birds where plumage coloration is very similar, and in some cases, almost identical. The Tyrant Flycatchers, a common group in North America, appear to the inexperienced eye as if they were all identical. In fact, they are so similar that many experienced birders have trouble making a positive identification.
Whenever you are first looking at a bird, look for any prominent patches of color. With many species, the most colorful areas will be found on the head, breast and along the wings. Look also for any obvious stripes or spots, whether colored or not. Streaks of color along the head and breast are also a good distinguishing trait.
Color in the tail is a very good diagnostic trait since few species have more than one color within their tail feathers.
Bear in mind that lighting conditions or weather can influence the look of a plumage, as colors seem faded or more vibrant under differing environmental conditions. This variation may be subtle but noticeable.
Size
The size of a bird is a very useful identification trait. Once you have become familiar with the birds in your field guide, a quick look at an unidentified bird will allow you to place the bird within a broad category, which is defined by the size of other birds.
For example, a bird may be easily categorized as “bigger than a Robin but no larger than a Crow”. This kind of ‘pigeon-holing’ (yeah, it’s a bad pun but I couldn’t resist) will allow you to concentrate on possible species that fit that size range, and it also means you can eliminate those species outside that size range. In this case, you could ignore most of the songbirds (for example, the warblers and sparrows) as they would be too small. Similarly, hawks, geese and herons would be far too large.
You should keep in mind, however, that some closely related bird groups can have a considerable size range. Woodpeckers, for example, can range in size from species that are smaller than a Robin to species that are larger than a crow.
Shape
A bird’s shape can also provide useful information for an identification. In general, bird groups (i.e., families) have a consistent body shape. Examples of this include the shorebirds (long legs, long beaks), ducks (short, squat bodies, rounded beaks) and falcons (long pointed wings, narrow tails). So if you are looking at a bird with a distinctive body or bill shape, this can help focus your efforts on a certain bird group within the field guide.
Body shapes you can use as identification clues can be expressed as either extreme or subtle traits. At the extreme end, there are birds such as the Marbled Godwit or American Avocet, whose extraordinarily long bills make these species rather easy to identify.
At the other end of the spectrum, subtle shape differences can also help to distinguish between similar-looking groups of birds. Some species of sparrows and finches can look quite similar, so much so that novice birdwatchers throw up their hands in despair when confronted with the myriad of possible species for that single bird. But if you look at just the bill, you will notice that sparrows and finches are very different. Sparrows have a longer, narrow, almost graceful-looking bill, which is perfectly suited for grabbing insects. By comparison, finches have shorter, stouter bills which are well suited for breaking open the seeds that finches prefer to eat.
Habitat
Some birds are known as habitat generalists in that they will be found in a wide variety of habitat types during their lifetime. An example of this is the Robin, which can be found in both cities and wilderness areas, and will use different habitats such as deep forest, open meadows, lakeshores, shrubby marsh areas, etc.. Habitat will not help you in identifying these species.
But there are other birds which are usually restricted to one certain habitat. Marsh Wrens, for instance, will spend the entire breeding season within the confines (or the immediate vicinity) of a single marsh, nesting, feeding and rearing its young deep within the marsh vegetation. So if you encounter a small, drab bird clinging to a cattail stem and singing its heart out, and you’re pretty sure it’s a wren, the chances are good that it’s a Marsh Wren and not one of the other wren species.
Habitat can be a useful trait to finalize an identification. Field guides will often mention if a species is generally found in a single habitat type.