They are terns, seagulls, avocets, gannets, skuas, guillemots, puffins, oystercatchers, ducks, geese, godwits, pheasants, magpies, sanderlings, storks, cranes, pelicans, herons, swans, loons, sparrows, pigeons, red-winged blackbirds, owls, cormorants, grebes, dunlins, crows, ravens, bald eagles, hawks, falcons, vultures, all of them vanishing from the landscapes of our homes, forests, sea coasts and minds. It rarely makes the news, and a world grown accustomed to ever-dwindling resources and diminishing life has not been paying attention. The warning of a Silent Spring, sounded sixty years ago like a trumpet's blare, has shrunken from a year-round emergency to the almost-meaningless ritual of Earth Day, celebrated just once a year. But last spring, during May and June, the world was awakened to shocking tales and heart-rending photographs of dead seabirds littering their breeding grounds all over the Northern Hemisphere, nowhere so vividly as in the De Petten Nature Reserve on