Among the smaller waterfowl, there are basically two types: There are ducks that dive, and there are those that dabble. Diving ducks, such as the tufted duck, scaup, scoter, harlequin and long-tailed duck, are birds of open, deep water, birds of lakes, coasts and the open ocean. Dabbling ducks, on the other hand, are birds of ponds and streams, shallow lakes and marshes. Some of them can be seen in considerable concentrations in Japan during the winter.
Pay a visit to one of the major city parks, or to almost any major river mouth between now and April, and you will find flocks of slender-necked northern pintail, compact Eurasian wigeon, stocky mallard or solid and bulky spot-billed duck. The pintail and wigeon in particular occur in huge flocks often numbered in the thousands. Among them, there are often smaller numbers of a rather different-looking bird: the shoveler.
The northern shoveler appears quite large, though it is its disproportionately large head that gives this impression. In body size, it is appreciably smaller than either the mallard or the spot-billed duck. Its plumage is distinctive. The male has an iridescent blue-green head, its chest is pure white and its flanks are chestnut, making it a very smart bird indeed. Like the other dabbling ducks, however, the shoveler has what is known as an eclipse plumage. The bright colors of the male serve the significant purpose of advertising, to compete with other males for the attention of females.
The females in turn are camouflaged with fine patterning in brown, so that when confined to their nests incubating their eggs they blend in well with marshland vegetation. That camouflage is important in reducing the chances that they may be found by predators — so you can imagine that the boldly marked males are highly conspicuous in contrast. Once the mating game has been played (and won or lost), the males quickly lose their brighter plumes and adopt a drabber version. This is more like the camouflage of the females. They spend several months during the middle and latter part of summer, even into autumn, in this guise, but once winter approaches they start shifting back into brighter colors again.
They change their colors and their behavior too, two characteristics that may indeed be linked in some important way. During winter, shovelers and other ducks are most often found in flocks, often very large ones, and in these numbers there is safety. The confusion factor is considerable, because when startled they all take wing together, and the rush of thousands of birds into the air is enough to stall the attack of many a predator. The individual that may have been the focus of the predator’s attentions is suddenly lost in the crowd, and if the predator switches its attentions to another, that too may quickly disappear into the melee.
Sometimes, peregrine falcons are drawn to these wintering sites of duck. However, if any of you have watched a peregrine attacking, you will have noticed that it is more than likely to try its luck on a bird that has for some reason become isolated from the flock, rather than one within the flock itself. From the predator’s perspective it must also consider safety. Flying at very high speed into a dense flock of slow-moving, heavy ducks is not a sensible approach. The risks of collision and injury to the predator’s own flying equipment — its feathers and wings — are too great.
rhaps it is that safety-in-numbers aspect of winter flock-life that means the dabbling duck males are able to return to their bright plumage at this time of year, rather than wait for spring. On the other hand, could it be perhaps that there are females among those wintering flocks to be wooed in readiness for the next breeding season?
Either way, shovelers and other dabbling ducks are steadily assuming their best plumage of the year. Wait for a clear, crisp winter’s day, when the sun is low and bright, and you will find that their iridescent colors seem to glow.
It is worthwhile to take a closer look at the flocks of wintering duck. Their bright plumage is inevitably the first feature that catches the eye. However, settle in and wait a while and you will find that their behavior is interesting and an equally effective way of telling them apart.
Mallard and spot-billed ducks are heavily built ducks that dabble away at the surface most of the time. Their stubby bills are suited to sieving pond weed from the surface of the water. The pintails, in contrast, have slender, longer necks and they use them to good effect reaching submerged plant food. They often lean forward, submerging their heads and necks to reach the vegetation lower down, while their long pointed tails rise vertically.
hovelers have an entirely different approach. The bill of the shoveler is a large affair, both longer and broader than those of any of their relatives. The Japanese name for this bird, hibiro-gamo,lects the noticeable broadness of its characteristic beak.
The edges of its beak are ridged, and these ridges have a very distinctive function. They serve to filter out food from the surface of the water. Although these are very small ridges, they function as sieves, similar to the way the baleen does for some of the whales. Whereas most of the dabbling ducks are almost exclusively vegetarian, the shoveler’s diet includes far more animal matter than any of its close relatives. They are able to sieve the surface waters of wet rice fields, marshes, ponds and lakes, and so catch a range of animal matter too, which can include insects, mollusks, crustaceans and even small fish.
Most duck species migrate north of Japan to breed, and the shoveler is no exception. It is only rarely encountered during summer. Now that autumn is here, however, and migration is underway, more and more shovelers are arriving to join the wigeon and pintail flocks. From early September to November, they are fairly common in Hokkaido, passing through on their southbound migration. Then, from mid-October onward they become more common in Honshu. Having spent the winter here, they seem much scarcer in spring, so perhaps they migrate northwards again by way of the continent.
And why are they called northern shovelers? Well, that is because they are not the only species of shoveler in the world, though they are the only ones living in the northern hemisphere.
Northern shovelers are by no means the only waterfowl to look out for this season. The wild swans, the whooper and Bewick’s are already here, working their way into the country from the north, as are the flocks of geese. Large numbers of white-fronted and bean geese are already pausing at their traditional sites in Hokkaido, and in another week or so they will be heading south for Honshu. With them this year are several rarities in the shape of snow geese and swan geese.
So, if your travels should take you to places such as Izunuma, in Miyagi Prefecture, to see the great winter goose gathering there, do look out for these very special extras among the main cast. And don’t forget to look out for the shoveler among the other dabbling ducks.