Graceful and agile in the air, the terns are the slender cousins of the gulls. Where the gulls typically lumber and flap, the terns flutter and dash. Terns may hover, and with the sun behind them, shining through their translucent wing feathers, they appear like tiny angels.

Inspiring and angelic though they are to the human eye, a small fish would see them very differently. Their sharp beaks, superior hovering skills and plunge-diving abilities all serve to convert small fish into tern flesh. While in flight, they spot their prey, fold their wings like darts and plunge. The unsuspecting fish in the water below is caught in the deftly controlled pincers of the bird's beak. Almost before the human eye registers what has happened, the tern surfaces again, takes to wing and is flying off, swallowing the tiny fishy morsel.

Terns call rivers, coasts, lakes and marshes home - wherever there are secure nesting sites and plentiful food. Many of them are migratory, linking countries in their extraordinary journeys that span the Earth's hemispheres. The ultimate record-breaker is the renowned arctic tern, which spends the northern summer nesting above the Arctic Circle and migrates via the European and African coasts almost as far south as Antarctica.

You won't see that species in Japan, but several of its relatives pass through Japanese waters, and some of them come here to breed. Japan's commonest breeding tern is the little tern (ko-ajisashi, Sterna albifrons).

This member of the family is distinctive, not just for its small size, but also for its conspicuous pattern. Where most terns have full caps, the little tern's black cap is broken by a prominent white blaze across the forehead and extending back toward its eyes. Where many terns have red or orange beaks, the little tern has a yellow bill with a black tip. Its legs and feet are bright orange, and like the gulls its toes are webbed.

Otherwise its plumage is completed in shades of gray and white, the tail short and mildly forked and the wings sharply pointed like the other members of its family.

The little tern was traditionally a fairly common breeding summer visitor in Honshu, Shikoku, Kyushu and the Nansei Shoto. It begins to arrive in Japan during March, and by September most families are leaving for the south, with just a few stragglers remaining into October.

Little terns have adapted to nest on sandy and pebbly coasts and along rivers with shingle and sand. There they gather to nest in small colonies from May to July. The males court their prospective mates with offerings of tiny fish. After successful courtship, the camouflaged eggs are laid in clutches of one to four among the stones, where they are incubated by the parents.

If you make the mistake of walking near such an area, you will soon find birds fluttering around your head. Watch if a cat or other predator approaches - the birds soon extend their noisy wheeling alarm flight to include swooping attacks in the hope of driving away the intruder.

Alas, such tactics achieve nothing against folk who innocently come across nests or set up their picnics along the riverside, or against the motorcyclists or fishermen who drive or wander through their colonies. Many nesting birds are disturbed and their eggs broken by such ignorant intruders.

If the little tern does survive the vulnerable egg stage, they hatch after about three weeks of incubation. The tiny chicks are almost as well camouflaged as the eggs. Crouching among the shingle they are easily missed by people engaging in waterside sports and recreation, and are easily trampled.

At colonies where I used to watch them in Britain, local people erected simple stick-and-string fences to mark where the colonies were and posted signs to warn people not to intrude. It was a simple but effective way of reducing inadvertent damage to the colonies. It would be reassuring to see more of that approach here.

Migrating little terns may appear in large flocks along coasts and at estuaries, but unfortunately their numbers are in decline because of habitat destruction here. Japan is not renowned for taking a proactive approach to nature conservation, nor is it renowned for natural rivers and coastlines. In fact, so many Japanese rivers now experience summer-long disturbance, and have been modified, straightened, canalized and generally targeted for construction, that the little tern as a species is under significant threat here.

This is not just an issue for Japan. The little tern is a migratory bird which spends the northern winter in Australia. Whatever Japan does to affect its breeding grounds has an impact on the numbers of birds returning to Australia each winter.

Here in Japan the situation is critical. The combination of recreational use of the remaining natural coastlines and astonishingly engineered rivers, along with the steady construction of new roads and bridges, has placed this bird in a particularly vulnerable position. Not far from Tokyo, at Atsugi in Kanagawa Prefecture, one of the largest colonies left in Japan is now seriously threatened by roadwork planned for the area.

Thoughtless "small" planning decisions made by local authorities may seem insignificant, but in fact they are contributing to global environmental degradation through death by a thousand cuts. Each "small" piece of the natural environment sacrificed has ramifications that are global in scale.

You can help by e-mailing the mayor of Atsugi in support of the little tern colony at [email protected] and joining in an appeal that has already attracted support from as far afield as Australia, Britain, Germany, New Zealand, Sweden and South Africa.