DNA analysis has enabled us to peer ever closer into the intricacies of what characterizes and distinguishes species, as well as the orders, genera and families they belong to.

But such challenging intricacies are for the taxonomist. The recent discovery of cryptic species has made it clear that field naturalists cannot hope to positively identify everything they see.

The goosander chases fish prey underwater.

A cryptic species is an astonishing revelation. On the whole, we identify species by their morphology or their behavior, so that naturalists can hope to be able to distinguish such species in the field.

Take ravens, for example. To look at, and according to traditional taxonomy, there is one raven species ranging through most of the Northern Hemisphere. Recent studies of ravens, however, have shown that there are, in fact, two. Ravens in California, though they look, sound and behave just the same as all the other northern ravens, are sufficiently genetically different that they must be regarded as a separate species. This is one species that no field naturalist can hope to identify.

Just how many such species are hiding out there is anyone's guess, but if such a thing can happen once, then no doubt it can happen many times. They are known as cryptic species because they are hidden among others, and, practically speaking, cannot be recognized -- unless you have invented DNA-scanning binoculars!

The common goldeneye (top) is a diving duck, while the pintail dabbles on the surface.

Taxonomists may rave over such esoteric differences, but those of us going out into the field face identification problems, and those are often best solved by focusing on behavior, not on DNA.

The season of feeding the birds on visits to ponds and lakes is about to end, and soon spring migration will be underway. The hordes of waterfowl wintering in Japan will make their way northward and westward to breeding grounds in continental Asia and Siberia. Perhaps the business of separating the more unusual species are still cause for panic rather than pleasure, in which case it is well worth focusing on the behavior of individuals to aid identification.

The local duck pond, likely to be a regular haunt for those readers with young children, provides an easy opportunity to observe ducks from three families: the dabblers, the divers and the sawbills.

Dabbling ducks, such as the northern pintail, are readily distinguished by their elongated, rather slender proportions and classic ducklike shape. The mallard and common teal are other species in this category. They feed by fidgeting and fossicking at the water's surface, using their bills rather like a sieve to extract food. They are usually herbivorous, and will readily come for food such as bread and grain.

The photo of the common goldeneye (a male) with the northern pintail reveals the basic difference between the diving and the dabbling ducks. The diving ducks are typically shorter in the body, dumpier in the head and have shorter, stubbier beaks. They seem to float higher in the water, giving them a more rounded appearance.

This group are noticeable, funnily enough, because they have a habit of disappearing. The goldeneye, tufted duck, greater scaup and their kin are active beneath the surface, diving beneath swans and other ducks, which welcome the food that the divers disturb. This can include a wide range of animal food, even shellfish. The divers submerge suddenly and power themselves along underwater using their feet; their wings remain closed.

Sometimes it is possible to follow them under water (watch for the trail of small bubbles escaping from among their feathers), so that one can predict where they will emerge. They pop up like a cork, suddenly bobbing up high in the water.

While the dabbling ducks are at home in shallow water, or close to the edge of a pond, the diving ducks are adept at reaching the bottoms of lakes and ponds, so they often feed further out from the edge. Tokyoites can visit Ueno Zoo and Shinobazu-no-Ike pond and see flocks of diving ducks there out in the middle of the water, while flocks of pintail gather near the edge competing for handouts.

A third group, the sawbills, is distinguishable by the ducks' special bill. Slender, often long, and saw-toothed along the edge, this is the specially adapted bill of a piscivore. Fish-eating birds, such as the goosander (or common merganser), the red-breasted merganser and, particularly at lakes and rivers in Honshu, the diminutive smew, also submerge, like the diving duck. They are more streamlined, though: They are built for speed, for the chase. Sawbill ducks target fish underwater and chase them down, catching them in their saw-toothed bills.

Like the diving duck, the sawbills' underwater propulsive power comes from their feet. Penguins, in contrast, "fly" underwater using their wings for propulsion and their feet only for steering.

The goosander is the largest of the sawbills in Japan, while the black-and-white smew with its panda-like face markings is the smallest. They gather with other ducks at wintering sites, but because they really do mainly live on fish, they are less frequently attracted to sites where people throw bread for the ducks. That said, however, I have found a few goosanders that have adopted the habit and regularly hang out with pintails and goldeneyes for a share of the bounty.

The sawbills all differ in another way from the dabbling ducks by nesting in holes; they find a rotten stump or a hollow tree and take it over for breeding in.

If you live in a well-wooded area then you may see another type of duck: the mandarin. The gaudy mandarin (the males have hugely enlarged, orange, sail-like wing feathers) are sometimes known as wood ducks, for like the North American wood duck, they live in forested areas feeding on nuts and seeds that they can forage for beneath the trees.

In winter, flocks of mandarins frequent ponds in wooded parks, preferring the shady corners. In summer they disappear to the mountains where they seem to prefer river valleys with large trees, for like the sawbills they are hole nesters.