Beginning birders usually identify species by comparing birds they see with illustrations or descriptions. To identify birds correctly, novices normally must examine them slowly in detail under favorable conditions. Experts, on the other hand, do not have to look so carefully; they have a mental picture that is far more detailed than any illustration. Their identifications are based on a variety of clues, considered singly or in combination. Here are some of the most important ones.

SIZE
The size of a bird, although it may be difficult to determine when the bird is far away or by itself, is a useful clue in identification. As you learn to recognize birds, you will quickly become familiar with their size relative to other species. Select a series of common and widespread birds of different sizes, such as the House Sparrow, American Robin, Rock Dove, American Crow, Canada Goose, and Great Blue Heron, and use these to gauge the size of other birds you see. You will soon be able to judge whether an unfamiliar bird is smaller than a House Sparrow, about the size of an American Robin, or somewhat larger than a Rock Dove. Very often in a flock of shorebirds or waterfowl, a single bird will stand out because it is larger or smaller than the others. If you already know that the other members of the flock are Sanderlings, for example, you will have a head start in identifying the single, unfamiliar bird. In cases where you cannot judge the size of a bird, its shape is the next feature to consider.

SHAPE
Shape is one of the most readily observed characteristics of a bird and one of the most important in identification. Your impression of a bird's shape will be influenced by several features. The body may be compact and stocky, like that of a European Starling or a member of the auk family, or it may be slender, like a Yellow-billed Cuckoo's or Red-breasted Merganser's. The neck may be very long, as in herons and the Anhinga, or very short, as in many small sandpipers. The legs, too, may be very long, as in most herons, or very short, as in terns. The bill may be conical, like that of a House Sparrow; slender and pointed, like that of a warbler or kinglet; heavy and pointed, like that of a Belted Kingfisher or a heron; decurved, like that of a curlew or Long-billed Thrasher; or hooked, like the bill of the American Kestrel and Red-tailed Hawk. The wings may be long and pointed, like those of terns, swifts, and swallows, or distinctly rounded, like those of quails. Tails vary greatly in shape. Some birds, like European Starlings and nuthatches, have short tails, while others, like gnatcatchers, thrashers, and wagtails, have very long tails. A bird's tail may be squared at the tip, like a Cliff Swallow's; notched, like that of a House Finch or Tropical Kingbird; deeply forked, like the tail of a Common Tern or Barn Swallow; rounded, like a Blue Jay's; or pointed, like a Mourning Dove's. Posture is often an important aspect of a bird's shape. Plovers tend to stand in a more upright position, with the head held higher, than sandpipers of similar size. Flycatchers usually perch with the body held almost vertically, rather than in the horizontal posture of warblers, vireos, and kinglets. Even among closely related species, there may be differences in posture: Yellow-crowned Night-Herons often stand in a more upright posture than do Black-crowned Night-Herons, and Rough-legged Hawks often perch in a more horizontal posture than Red-tailed Hawks.

Many species can be identified by shape alone. For example, virtually all North American ducks have a distinctive head shape; when seen in profile, they can often be identified by this feature.

Similarly, veteran hawk watchers routinely identify birds at ranges so great that the hawks appear as mere specks in the sky; they do this in part based on the wing-to-tail ratio. Even in as large a group as the shorebirds, almost every North American species has a unique outline formed by a combination of body size, length and shape of bill, and length of wings and legs. Of all a bird's characteristics, its silhouette is the least subject to change. If you really know a species' shape, you are unlikely to be misled by unfamiliar aspects of its plumage.

COLOR AND PATTERN
Color and pattern are important, too. The brilliant red of a male Northern Cardinal is often one's first clue to the identity of this bird, visible before its conical bill can be seen and before one is familiar with its distinctive, tail-pumping flight. The solid blue of male Indigo Buntings and Mountain Bluebirds at once sets these birds apart from all others. In much of the continent, a flash of bright orange and black in the treetops can instantly be called a Northern Oriole. Before a beginning birder learns the distinctive shape and manner of flight of an American Kestrel, its colors -- bluish-gray and rufous in the male, rufous-brown in the female -- enable him to identify this small falcon. If you note that a distant goose is white with black wing tips, you have narrowed the possibilities to only two species, the Snow Goose and Ross' Goose. Among the spotted thrushes, a bird in which only the tail is rust-colored is a Hermit Thrush; one with rust on the head and back is a Wood Thrush; a bird whose upper parts are wholly tawny is a Veery; while a bird with no rust or tawny in the upperparts is either a Gray-cheeked or Swainson's thrush.

Carefully noting the color and pattern of a bird is essential in identifying it. Watch for wing bars; vireos, for example, can be sorted into two groups, those with wing bars and those without. Other wing patterns can be helpful, too, especially if the bird is in flight. The black-and-white pattern of a flying Willet is diagnostic, as are the red shoulders of Red-winged and Tricolored blackbirds, and the flashes of white in the wings of White-winged Doves, Red-headed Woodpeckers, Northern Mockingbirds, shrikes, and male Phainopeplas. Watch for rump and tail patterns. A departing Northern Flicker can be identified at a glance by its white rump; the pale buff rump of a Cliff Swallow or Cave Swallow quickly eliminates all other swallows. A yellowish or greenish warbler with large yellow tail patches must be a Yellow Warbler, while one with large white tail patches and a yellow rump is likely to be a Magnolia. White outer tail feathers mark the juncos and a variety of open-country birds: meadowlarks, pipits, Horned Larks, and Vesper Sparrows. A large flycatcher with a white tail tip must be an Eastern Kingbird, while in the West, a kingbird with white outer tail feathers must be a Western.

Look carefully at the pattern of the head. Watch for eyebrows, eyerings, eyelines, mustaches, or throat patches; note the color of the crown, ear coverts, and lores. Take special note of any unusual color pattern: the red head and yellow body of a male Western Tanager, the golden-buff nape of a male Bobolink, the white sides on the rump of a Violet-green Swallow, and the rufous rump of the gray Lucy's Warbler are all diagnostic. The pattern of many species makes them easy to identify. Flying waterfowl and many warblers usually can be recognized by pattern alone. When other features are all but invisible, particularly in poor light or at great distances, a bird's distinctive pattern can often be discerned.

BEHAVIOR
Many birds walk, swim, or fly in so characteristic a manner that behavior by itself can permit identification. Given an unlabeled specimen of a Water Pipit, most birders are not likely to recognize it at once, yet they can identify the living bird from hundreds of yards away by its bounding, stuttering flight or its habit of emphatically pumping its tail when on the ground. Some behavioral clues are obvious, like the big, splashy dives of Northern Gannets and Ospreys, the constant nodding of a yellowlegs, the head-bobbing motion of a swimming coot, the zigzag flight of a Common Snipe when it is flushed from a wet meadow, or the mothlike flight of a Common Poorwill. Others are subtle, such as the flight mannerisms of kittiwakes and the wing- and tail-flicks of flycatchers. Behavioral clues are almost unfailingly reliable and can help in identifying birds under a variety of circumstances. The differing flight styles of hawks, for example, or the various feeding postures of shorebirds can be used to identify them almost at the limit of visibility.

VOCAL CUES
In many situations, it is easier to hear birds than to see them. Whether you are in the rain forest of the Northwest, the woods of New England, or the cypress swamps of the Carolinas, you are certain to hear many more birds than you see. The vocalizations of birds may be divided into two rough categories: songs and calls. Songs are usually given by adult males on territory during the nesting season, but may also be heard during migration and, in some species, during the winter as well. In certain species, such as the Rose-breasted Grosbeak and Northern Mockingbird, females as well as males may produce songs. Many songs are rather complex, like those of the Winter Wren and most wood warblers, but some are very simple, like the short, metallic tslit of Henslow's Sparrow. Calls, or call notes, are generally more simple, and are often given throughout the year under a variety of situations to express alarm, to maintain contact with other members of a flock, or during interactions with a mate or young.

Knowing the songs and calls of a region's birds will enable you to identify a far higher percentage than you could with binoculars alone. Identification by voice is almost always reliable. The shorebirds, for example, have flight calls, given at all times of the year, that are absolutely distinctive. Every shorebird native to North America, as well as vagrant species from the Old World, can be identified be these notes alone. Thus, if you are familiar with shorebird voices, you can identify the birds with certainty anywhere at any time of year, whether they are breeding in the Arctic, migrating through our latitudes, or wintering in South America. You can identify them even in darkness, and up to the limits of audibility. All North American songbirds, as well, have distinctive voices; in many cases, even their minor calls -- lisps or chips -- are recognizable. For example, of the large New World subfamily of wood warblers, about fifty fairly closely related species breed in North America. All have songs that can be learned readily; in fact, their songs differ in some cases more markedly than their plumages. Each song can be distinguished and mentally catalogued according to a variety of characteristics: pitch, cadence, duration, loudness, frequency of utterance, and quality. Although the song structure of a species may vary slightly from region to region, the quality of the song will almost always remain recognizable.

HABITAT AND RANGE
Most people know that ducks and gulls are water birds and that thrushes are birds of the forest, but few beginning birders are aware of how specific most species are in their habitat requirements. Although these requirements may vary somewhat according to region and season, they are still quite rigid; experienced bird watchers expect to see certain birds in certain habitats. Warblers are as selective as any group: Tennessees breed in tamarack, Ceruleans in tall hardwoods, Blackpools in stunted spruce, Prairies in mangroves and red-cedar pastures, Palms in bogs, and Mournings in raspberry thickets. These are hard-and-fast rules during the breeding season, but migrants are less selective and may appear anywhere. Other species are specific in their choice of habitat even as transients. In the Northeast, two uncommon fall migrants are remarkable in this respect; Orange-crowned Warblers frequent the tops of old goldenrod blooms along the coast, and Connecticut Warblers prefer damp meadow edges and hardwood swamps that have an open understory of plants such as clethra and silky dogwood, with jewelweed underfoot.

Knowing habitat preferences greatly increases the chances of finding particular birds; it can also limit what we expect to find. In many cases, habitat by itself helps us to identify species. For example, even if they can barely be seen or heard, blackbirds in northern bogs are almost certain to be Rusties. Finally, the range of most birds is determined in large part by the availability of a specific habitat. Although the ranges of most species are continuously expanding or contracting, they can nonetheless be geographically defined or mapped. Knowledge of range enters into virtually every identification, usually as a subconscious first consideration. So too does an awareness of the average arrival and departure dates of migratory species.

BECOMING AN EXPERT
To the uninitiated, the identifications made by experienced birders often seem to approach wizardry. Experts, rather than comparing the bird they have seen with illustrations in a field guide, weigh a number of attributes that together give the species a distinctive personality. The better you know a species, the more ways you have to identify it. Many North American birds have three or even more identifiable plumages, which can be bewildering at first, until one realizes how many factors are invariable: shape, voice, behavior, and range.

LOOKING AT BIRDS
There is no secret to becoming skilled in identifying birds: Just look and listen. Observation may seem simple at first, but you will progress faster if you look attentively and repeatedly, even at common species. For many beginners, examination stops and binoculars come down the moment the bird is identified. In fact, this is the time to start looking. Make the effort. Imagine, for example, that this is the last Downy Woodpecker you will see for a long time, or that you will soon be asked to describe or even draw it. If you have difficulty getting a firm grasp on a bird's appearance, first look at its eye, and to force yourself to look closely, try to ascertain the color of the iris. Then study the size and shape of the bill and its length in relation to the distance separating its base from the center of the eye. Next, extend your study of the bird's proportions to the length of its legs and to the position of the folded wing tips in relation to the tip of the tail. From these observations, proceed to an examination of the bird's coloring and patterns. This deliberate approach might seem tedious, but birds lend themselves to careful observation, and you will almost certainly find it engrossing and rewarding. You will soon discover that you can memorize birds in much the same way you memorize human faces. It is possible to acquire a permanent familiarity with a seemingly limitless number of bird species, but to do so you must look carefully. Most expert bird watchers spend much time simply studying the appearance of birds, even familiar ones. This enjoyable exercise results in a far more detailed acquaintance than is required for simple identification, but it also makes one aware of the differences between species that superficially appear to be similar. Bear in mind that you can know what a bird looks like by looking at it. This sort of bird study demands fairly close-range and leisurely observation, but do not pass up a chance to watch a distant bird -- you may be surprised at how much you can see. With good light and good binoculars, you can identify distinctly patterned birds as small as warblers, in flight, even overhead, at a great distance, but you will not know this until you try it.

Looking at museum specimens or, better yet, at live birds trapped at a banding station, can also be extremely helpful. Side-by-side comparison of similar species can reveal differences that may help you in field identification. Juxtaposing and comparing eight or ten species of warblers, for example, will demonstrate as no field guide can the diversity that exists within this group. You will discover how much these species vary in size, bill shape, wing length, rictal bristles, or any number of small details. Studying specimens or captive birds will also help you to learn about the arrangement of feathers: which ones are involved in the wing bars, for instance, and how the tail feathers are shingled, with the central pair, or "deck feathers," on top and the outermost underneath. These insights will help you to understand what you see in the field.

LISTENING TO BIRDS
Learning bird songs may seem difficult at first, but we learn them much as we learn melodies, by attentive and repeated listening. You can be more or less energetic in acquiring this familiarity with bird voices, but you will progress faster if you make it a rule to track down every unfamiliar call. This may initially seem overwhelming, but your ear will soon become remarkably good at resolving a tangle of noise into recognizable voices, and a dawn chorus of bird song will become a delightful exercise in auditory discrimination. Try to attach a set of associations to each bird vocalization by describing it to yourself or comparing it with other sounds you know; make your mental description of sounds as detailed as possible. If you can whistle, try to copy the sound you are learning; to imitate it acceptably you will have to listen closely to the model. The more characteristic sounds of most North American birds are available on commercially produced recordings. Although listening to records, tapes, or, more recently, compact discs, removes the learning process one step from direct experience, it will at the very least make you sensitive to aspects of bird song that make the voices of each species distinctive and recognizable. Even the least expensive recording equipment can be helpful, too, since listening to your own tapes allows a comparative or analytical approach to the study of bird song. Moreover, playback of a reasonably good field recording will often attract the singing bird and enable you to observe it more closely.

CONCLUSION
Bird watching has attracted an ever increasing number of devotees in North America. The science -- some would say the art -- of bird identification has been considerably advanced and refined in recent years. Field problems have been clarified or resolved, vocalizations studied, behavioral clues detected, and distinguishing characteristics isolated. As a result, bird watchers of today are immeasurably more sophisticated than those of only a few decades ago. Bird identification is now a field in which one can quickly achieve a high degree of competence, with all its attendant satisfactions. And bird watching -- need it be said? -- is a pursuit with many, many rewards.

Copyright 1996 Alfred A. Knopf. All rights reserved.