Out of Control!
Exploding numbers of snow geese are bad news for Midwest farmers and an entire Far North ecosystem
- Lisa Drew and Chris Madson
- Dec 01, 1997
For vast numbers of migrant birds every spring, arrival at Canada´s La Pérouse Bay has long meant access to lush grass and sedges. But no more. Now the birds find barren flats of salt-encrusted mud and exposed peat increasingly taking over the landscape--not only at this study area on the western side of much larger Hudson Bay, but in the whole region. This spring will be no exception. Studies have found that more than 60 percent of the salt-marsh vegetation in La Pérouse Bay is now either destroyed or damaged to the point where it does not nourish birds.
Species already affected include American wigeons, northern shovelers, yellow rails, stilt sandpipers, Hudsonian godwits and short-billed dowitchers. Early results of a collaborative study by U.S. and Canadian scientists indicate that the combined numbers of those species in La Pérouse Bay have decreased to 10 percent of their 1980 levels. But that preliminary figure does not tell the whole story. This past June, ornithologist Robert Rockwell of the American Museum of Natural History was so frustrated by the bay´s bird scarcity that he sent 12 researchers into an 8-square-mile study area for 3 days in search of certain species. They found none of the first three species listed above. "The tapping noise made by the yellow rails used to be one of the sounds of night in the area," says Rockwell. "No more."
This phenomenon occurs mostly in this particular habitat: Waterfowl numbers have been rebounding in North America from lows in the 1980s. Still, the declines have far-reaching implications. "We´re not talking about one of the most abundant biomes around," says waterfowl biologist Ken Abraham of the Ontario Ministry of Natural Resources. "We´re talking about a strip of salt marsh a few hundred yards wide along arctic and subarctic waters. It might cover a long distance, but it´s just this narrow, super-productive zone that supports the highest diversity of plant and bird species in the overall ecosystem. And we´re losing it."
What´s behind the destruction? Here´s a hint from a 1996 scientific paper by University of Toronto botanist Diane Srivastava: "The processes resulting in the loss of vegetation on these coastal flats are similar to those that have led to the destruction of vegetation by livestock in the Sahel region of Africa."
Eating machine: In other words, the culprit is a hardy eating machine. And for anyone who knows the feeding habits and recent history of North American waterfowl, that is a broad hint. The simple answer is not domestic livestock but a wild bird--the snow goose, a creature so successful that even the disastrous conditions of its nesting grounds are hardly slowing it down. U.S. Secretary of the Interior Bruce Babbitt recently called the species "totally out of control."
The mid-continent population of the lesser snow goose, one of two subspecies, is particularly on the rise: In the last quarter of a century, it has increased from 2 million to 5 million. The somewhat larger greater snow goose, which migrates along the East Coast, also has exploded in numbers--from 50,000 three decades ago to 12 times that today.
The bird itself is only part of the explanation. The fuller answer involves the human history of the United States: The Far North devastation would not be occurring without the dwindling of Gulf Coast marshes and the growth of Midwest farms. Still, the key to the puzzle is the snow goose´s unique combination of attributes and abilities--some of which are shared by other species, but all of which exist only in this one white bird.
Tough bills: Equipped with reinforced, serrated bills, snow geese can rip roots and rhizomes from the ground. That ability has served them well at both ends of their migratory routes. For the mid-continent lesser snow goose, until the last few decades, prime winter habitat has been the narrow complex of coastal marshes along the Gulf of Mexico from the Mississippi Delta to Galveston Bay. The birds traditionally wintered within 15 miles of the Gulf Coast, where they grazed on grass or grubbed for buried parts of marsh plants, most of which grow from a thick network of fleshy stems, roots or tubers underground.
In the Far North, the geese also pull or grub for plants--even from thawing ground--eating the below-ground tissue and discarding dead leaves and shoots. The birds often strip away sod, creating shallow pools. Later in the season, the birds graze on the new growth of remaining grasses and sedges.
Adaptable appetites: After the early part of this century, the quality and quantity of available food along the Gulf Coast no longer limited the size of the snow goose population. Increasing human settlement and development, as well as degradation and filling of coastal marshes, forced the birds to find new groceries--an option not open to species restricted to wetlands. In the late 1940s, counts of snow geese on rice fields inland from the Texas marshes rose from almost zero to more than 10,000 birds. At the same time, the flocks were learning to stop farther north for the winter to feed in corn and wheat stubble. By the late 1970s, snow geese were spending the winter as far north as Iowa.
Social tendencies: Snow geese migrate, forage and nest in huge congregations. The reasons are not fully understood, but one benefit is probably the sharing of defenses against predation. Large flocks, however, require large meals. As productive as Gulf Coast wetlands once were, their provisions had a limit, and they served as brakes on the growth of the ravenous flocks. Even in warm marshes, plants may take several years to recover from goose abuse.
On their summer grounds, snow geese are now spreading from coastal areas into surrounding tundra. The feeding has exposed the dark peat soil of tundra in some areas to wind and water erosion. A thousand years of topsoil buildup can disappear in one or two summers. Or it may turn salty as the black dirt absorbs solar energy and evaporation increases, drawing water up from subsoils and gravel below.
Strong legs: The geese are not immune to the devastation of their nesting grounds: Adult females in the colony at La Pérouse Bay are 15 percent lighter now than they were in 1970. They lay fewer eggs than they did 30 years ago. But soon after goslings hatch, they are able to follow their parents as far as 50 miles to find forage--on foot. At that point in the season, neither the chicks nor the molting parents can fly. These treks retard the goslings´ growth and expose them to predators, and more than 60 percent die before they fly at six weeks of age. Still, the long walks allow the species to prosper even as the birds ravage more habitat. And female young will return to the new locations to raise their own young.
Long lives: If snow geese were shorter-lived birds, the loss of goslings to the habitat destruction of breeding grounds would reverse the population explosion. But snows commonly live and breed into their teens, and a few hardy females may continue to live and nest past the age of 20. Life expectancy of adults has actually increased since the 1950s. If they raise two young to adulthood, they´ve replaced themselves. Any more, and the population continues to grow even if large numbers of young die.
Search for solutions: U.S. and Canadian waterfowl experts are calling for an all-out effort to reduce the population of mid-continent snow geese to a level that can be sustained by their arctic and subarctic habitats. Waterfowlers may be allowed to use hunting techniques that have been banned in the past because they are so effective, such as electronic calls or baiting. "There´s a finite amount of good habitat, and we´re running out of it," says Bruce Batt, chief waterfowl biologist with the nonprofit group Ducks Unlimited. "Now is the time to intervene."
Lisa Drew is a senior editor of this magazine. Chris Madson writes from Cheyenne, Wyoming, where he is editor of Wyoming Wildlife magazine.