Concerns over the introduction of alien species to environments that have no protective mechanisms against them are beginning to filter through the bureaucratic system in Japan to the point where action is being contemplated — or even taken.
|The mute swan comes from Central Asia, and may be causing problems in Japan.|
The steady spread of the mongoose across Okinawa and Amami-Oshima threatens endemic amphibians, reptiles and birds. American raccoons spreading across Hokkaido threaten local hole-nesting birds and mammals ill-adapted to defend themselves against this agile, tree-climbing omnivore.
Other exotic introductions from brown tree snakes to black bass undermine and threaten Japanese ecosystems from subtropical forest to temperate lakes, and it is high time a concerted policy was promoted for dealing with aliens.
Among the many issues this will raise is: “What should we do about the mute swan?”
The mute swan is the world’s heaviest flying bird, and ranks alongside the trumpeter swan as the largest of all the waterfowl. Its specific identity was not recognized until 1789, by Gmelin; Linnaeus was aware of its existence some three decades earlier, but he mistakenly considered it a domesticated form of the whooper swan.
Originally a wild bird that bred on the steppe lakes of central Asia, the inappropriately named mute swan (it is not silent) is now perhaps the most familiar of all the swans worldwide. In its native range it is shy and unapproachable, but it was domesticated long ago by the Greeks and Romans, as a bird for the table.
It has been introduced widely and, tame and confiding, can be found on city park lakes even in the heart of some of the world’s busiest cities, such as London and Tokyo. Today, introduced populations of the mute swan are resident and breeding across much of the temperate zone.
In Japan, it seems to have been introduced to enhance the sightseeing experience at various parks with lakes throughout the country. Birds that escaped in the Onuma region of Hokkaido established a breeding population at Lake Utonai near Tomakomai.
The mute swan today has a scattered distribution from Europe across central regions of Asia through northern China and Japan. Some birds are of domesticated origin and others wild, but it is no longer possible to distinguish them.
Those mute swans that breed in the northern parts of their range, in southern Scandinavia in the west and Hokkaido in the east, are migratory, with Scandinavian birds wintering in Baltic coastal regions, and north Japanese birds wintering in central Honshu. Most of the remainder tend to be resident.
Mute swans are readily distinguished from the other white swans of the northern hemisphere because of their bright reddish-orange bill, which is black at the base and has a black knob, and because of its habit of swimming with its wing feathers raised in a strong arch and its neck curving gracefully in an S-shape. Adults are, like the “northern swans,” entirely white, with black legs. Young birds are dark grayish-brown and have gray-pink bills with a black base and gray legs and feet. An albino “Polish” form is all white, even as a cygnet.
The wing beats of other swans are silent, or merely make a quiet whooshing sound audible only at close range, as do the wings of other large heavy birds. The beating wings of the heavy mute swan, however, make a highly audible, distinctive, throbbing “waou, waou, waou” noise. The four northern swans have rather short tails (in flight their feet reach just to the end of the tail), but the mute swan has a longer, pointed tail that extends well beyond its feet.
The “mute” swan has its own repertory of hisses, snorts and grunts; it is only mute in comparison with the other northern species, which have haunting whooping and bugling calls.
It is a bird of lowland waters, ponds, lakes, reservoirs, streams and rivers, and also occurs on brackish or salt water in sheltered coastal bays, estuaries or lagoons.
Breeding begins in April, when huge nest mounds made of vegetation are built close to water, on banks or islets, often among reeds or other tall growth in swamps. It lays 4-7 eggs (rarely up to 12), which are incubated by the female for 35-38 days. The fledging period is long, at 120-150 days, and so it is unable to breed in sub-Arctic boreal or tundra regions where summers are shorter than this. For that reason it cannot extend its range northward into that of the whooper swan or Bewick’s swan.
At some localities (Abbotsbury Swannery in Dorset, England, for example, and in parts of Denmark) large numbers breed in close proximity in what amount to loose colonies. Large numbers also gather after breeding to form post-breeding molt concentrations.
Throughout most of its range the mute swan is strongly and aggressively territorial during the breeding season. Males, on water, raise their inner wing feathers in an arch, rest their necks back on their shoulders and swim powerfully and jerkily to intimidate intruders. On land, with the neck feathers raised, and beating their wings vigorously, they are capable of injuring people and dogs and driving them away from their nests.
European swan populations are believed to be increasing, though there have been serious local declines resulting from poisoning caused by the birds’ ingesting spent lead gunshot or lead weights lost or discarded by anglers.
Asiatic populations are far less well known and less well studied, and therein lies a problem. Ornithologists and birdwatchers tend to look down on “escapees,” “introduced” or “feral” species, and so don’t bother to study them. As a result very little is known about where they are, how many there are and the extent of their impact. In particular, the mute swan has been in Japan ignored even though it has established a permanent population here. Does the mute swan compete with other waterfowl, invading their ecological niches, or has it merely found and filled a vacant ecological niche here in Japan?
The problem is on-going: Black swans have now also been introduced from Australia. I have encountered them at several localities in Honshu and Kyushu where they had clearly been released as tourist attractions. Have any of them bred? Are they spreading? What problems are they causing?
If you have seen any black swans, please write and tell me where and when; I am interested in monitoring them.