The Staging of white geese at Tule Lake in northern California in November is one of the most imposing—and dependable—wildlife spec­tacles in the world. At first one thinks of it only as a phenomenon of numbers—it's been possible in recent years to see as many as three hundred thousand geese here at one time. What a visitor finds as startling, however, is the great synchronicity of their movements: long skeins of white unfurl brilliantly against blue skies and dark cumulonimbus thun­derheads, birds riding the towering wash of winds with balletic grace, with a booming noise like rattled sheets of corrugated tin, with a furious and unmitigated energy. It is the life of them that takes such hold of you.

I have spent enough time with large predators to know the human predilection to overlook authority and mystery in the lives of small, gregarious animals like the goose, but its qualities are finally as subtle, its way of making a living as admirable and attractive, as the grizzly bear's.

Geese are traditional, one could even say conservative, animals. They tend to stick to the same nesting grounds and wintering areas, to the same migration routes, year after year. Males and females have identical plumage. They usually mate for life, and both sexes care for the young. In all these ways, as well as in being more at ease on land, geese differ from ducks. They differ from swans in having proportionately longer legs and shorter necks. In size they fall somewhere between the two. A mature male lesser snow goose (Chen caerulescens), for example, might weigh six pounds, measure thirty inches from bill to tail, and have a wingspan of three feet. A mature female would be slightly smaller and lighter by perhaps half a pound.

Taxonomists divide the geese of the Northern Hemisphere into two groups, "gray" and "black," according to the color of their bills, feet, and legs. Among black geese like Canada geese and brandt they're dark. Snow geese, with rose-pink feet and legs and pink bills, are grouped with the gray geese, among whom these appendages are often brightly colored. Snow geese also commonly have rust-speckled faces, from feeding in iron-­rich soils.

Before it was changed in 1971, the snow goose's scientific name, Chen hyperborea, reflected its high-arctic breeding heritage. The greater snow goose (C. c. atlantica)—alarger but far less numerous race of snow goose—breeds in northwestern Greenland and on adjacent Ellesmere, Devon, and Axel Heiburg islands. The lesser snow goose breeds sightly farther south, on Baffin and Southampton islands, the east coast of Hudson Bay, and on Banks Island to the west and Wrangel Island in Siberia. (Many people are attracted to the snow goose precisely because of its association with these little-known regions.)

There are two color phases, finally, of the lesser snow goose, blue and white. The combined population of about 1.5 million, the largest of any goose in the world, is divided into an eastern, mostly blue-phase population that winters in Texas and Louisiana, and a white-phase population that winters in California. (It is the latter birds that pass through Tule Lake.)

The great numbers of these highly gregarious birds can be misleading. First, we were not certain until quite recently where snow geese were nesting or how large their breeding colonies were. The scope of the problem is suggested by the experience of a Canadian biologist, Angus Gavin. In 1941 he stumbled on what he thought was a breeding colony of lesser snow geese, on the delta of the McConnell River on the east coast of Hudson Bay—14,000 birds. In 1961 there were still only about 35,000 birds there. But a 1968 survey showed 100,000 birds and in 1973 there were 520,000. Second, populations of arctic-breeding species like the snow goose are subject to extreme annual fluctuations, a boom-and-­bust cycle tied to the unpredictable weather patterns typical of arctic ecosystems. After a series of prolonged winters, for example, when per­sistent spring snow kept birds from nesting, the Wrangel Island population of snow geese fell from 400,000 birds in 1965 to fewer than 50,000 in 1975. (By the summer of 1981 it was back up to 170,000.)

The numbers in which we see them on their wintering grounds are large enough to be comforting—it is hard at first to imagine what would threaten such flocks. Snow geese, however, face a variety of problems. The most serious is a striking loss of winter habitat. In 1900 western snow geese had more than 6,200 square miles of winter habitat available to them on California's Sacramento and San Joaquin rivers. Today, 90 percent of this has been absorbed by agricultural, industrial, and urban expansion. This means 90 percent of the land in central California that snow geese once depended on for food and shelter is gone. Hunters in California kill about twenty percent of the population each year and leave another four to five percent crippled to die of starvation and injuries. (An additional two to three percent dies each year of lead poisoning, from ingesting spent shot.) An unknown number are also killed by high-­tension wires. In the future, geese will likely face a significant threat on their arctic breeding grounds from oil and gas exploration.

The birds also suffer from the same kinds of diseases, traumatic ac­cidents, and natural disasters that threaten all organisms. Females, for example, fiercely devoted to the potential in their egg clutches, may choose to die of exposure on their nests rather than to abandon them in an unseasonable storm.

In light of all this, it is ironic that the one place on earth a person might see these geese in numbers large enough to cover half the sky is, itself, a potential threat to their existence.