FIELD IDENTIFICATION

Field identification is an acquired skill, but it helps if you have a natural aptitude. Having a good eye and ear, patience, persistence, the capacity to be quiet and the ability to really watch birds are invaluable attributes. There is, however, no substitute for knowledge of the subject based primarily on field experience. As one gains in experience, the range of species with which one is familiar steadily expands, but every so often one comes across unfamiliar birds, particularly when visiting a new area. An intimate knowledge of the variations in the appearance, behaviour, voice, habitat and distribution of familiar species is often vitally important when identifying an unknown bird. Such knowledge allows direct comparison between the bird one is seeking to identify and species with which one is already familiar. 

An essential ingredient of successful field identification is to make careful field notes of the characters observed. Ideally, this should be done with every unfamiliar bird, and even with familiar species whenever one observes interesting variations in plumage, behaviour etc. Field notes should cover size and shape, plumage coloration and pattern, behaviour, voice, habitat and any other seemingly relevant details such as weather conditions, names and addresses of other observers etc. 

When confronted with an unfamiliar bird, it is first necessary to establish to which family it belongs (and then, in the case of large and complex families, to decide to which subdivision, or genus, it belongs). Only then can the process of identifying the species seriously begin. The ability to separate one family from another is the foundation of successful field identification. For experienced observers, the process of identifying the family becomes second nature, but for beginners this first step often proves more difficult than separating one family member from another.

Shape and Size
Shape and size are critically important at the first level of field identification, that of determining to which family a bird belongs. Many beginners neglect this first level, making the mistake of jumping straight into species level identification, but there is little point in knowing how to separate one sandpiper or pipit from another if one cannot tell a sandpiper from a plover or a pipit from a lark in the first place. Almost all families have a characteristic shape, or range of shapes, which differentiates them from other families. In general, this characteristic appearance derives largely, or so it seems, from a combination of head/bill shape, neck length, wing shape, tail shape, leg length and foot shape. All these aspects of a bird’s appearance should be carefully examined.

In some cases the structural differences between families are quite subtle, and the field observer will need to use shape and size together with other characters such as plumage pattern, behaviour or voice in order to clinch the family identification. Differences in shape and size are often very important at the species level also, especially when large and structurally diverse families are involved.

Overall size can be difficult to judge accurately. Birds often seem to vary in size according to what they are doing: a soaring bird of prey seems larger than one that is gliding rapidly downwards with sweptback wings. Mist or haze makes birds seem bigger than they really are. Sometimes, the presence of accompanying birds of known identity will allow accurate size comparisons to be made, but even then there may be potential problems. Optical size illusion when looking through a telescope can make the nearer of two identically-sized birds seem smaller than the other (and likewise the front birds in a flock can appear smaller than those of the same size that are standing further back).

Shape can similarly have its pitfalls, since it can vary markedly according to what a bird is doing (e.g. fluffed out in cold weather or when bathing, standing tall and alert, or hunched up when facing into strong winds), but usually at least some of the distinctive characters can still be observed whatever posture is being adopted. Feather moult or damage can also affect overall shape and thus cause identification problems. Not only are distinctive feathers sometimes lost outside the breeding season (e.g. the projecting tail feathers of skuas), but missing flight and tail feathers can create misleading impressions (e.g. Western Marsh Harriers and dark morph Booted Eagles with missing tail feathers that superficially recall Black Kites).

A close attention to shape and size is critically important in separating relatively similar-looking families

Feather moult or damage can affect shape and cause identification problems

Bird Topography
A good knowledge of ‘plumage topography’, the relative positions and names of the various tracts of feathers that combine to cover the bird and which add so much to its distinctive shape and appearance, plus a familiarity with the names and positions of the different ‘bare parts’, is an essential tool of bird identification. We cannot overstate its importance, yet a surprisingly large number of birders shy away from the finer points of this subject and in consequence are severely handicapped when trying to identify birds.

There are two basic types of feather: contour and down. It is the former which concern the field observer, for the down feathers are not usually visible on fledged birds (other than newly fledged owls), being an underlying, insulating layer. Other less important feather types are bristles and filoplumes. The former are found in many species, typically in the form of the fine rictal bristles situated around the base of the bill. The latter, which are fine, hair-like plumes, are usually equally inconspicuous (cormorants being an exception).

The contour feathers are generally divided into two groups, the body feathers (which include the wing coverts) and the flight and tail feathers (the former consisting of the long wing feathers known as the primaries and secondaries).

Plumage topography varies slightly between families, but the general pattern remains the same. We recommend a thorough study of the topographic illustrations, since this guide can be effectively used only if the terminology and location of the different feather tracts are fully understood. Some structural or plumage features require further explanation:

Arm: inner part of the wing (before the carpal joint)
Carpal joint: ‘wrist’ joint on the wing (between ‘hand’ and ‘arm’)
Cere: bare skin covering the base of the upper mandible of raptors, pigeons and some gamebirds
Culmen: the dorsal ridge of the upper mandible
Emargination: notch on the outer and inner web of (usually) the outer primaries
Gonys: the ventral ridge on the lower mandible where the two halves of the jaw meet (prominent in
divers, gulls etc.)
Gular feathering: wedge of feathering on the underside of the lower mandible
Gular stripe: dark stripe down the centre of the throat (e.g. in some Accipiter hawks)
Hand: outer part of the wing (beyond the carpal joint)
Leading edge: the forward edge of the wing. Generally referred to when there is a dark or pale band along
the leading edge
Mirror: subterminal white spot(s) on the tips of the outer primaries of gulls
Nail: nail-like projection at tip of upper mandible of wildfowl and some other birds
Occipital plumes: long plumes projecting from the back of the head (e.g. in herons and egrets)
Orbital ring: narrow ring of bare flesh surrounding the eye
Primary projection: distance between the tip of the longest tertial and the tip of the longest primary on
the closed wing