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Millions of snow geese imperil fragile ecosystem

Far-northern breeding grounds are devastated. A major culprit: expanded farming in US Midwest.

By Moises Velasquez-ManoffStaff writer of The Christian Science Monitor / September 25, 2008

Snow geese have denuded the vegetation. Only reddish salt-tolerant salicornia thrives – except where researchers fenced geese out.

Courtesy of The Hudson Bay Project

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In the mid-1980s, scientists began noticing a curious phenomenon in goose nesting grounds along the western edge of Canada’s Hudson Bay. Once-verdant salt marshes were transforming into barren mud flats. With plant cover gone, evaporation accelerated and the soil quickly became too salty for all but a few species. By August, only the reddish salt-tolerant salicornia plant remained in a landscape often littered with dead, bleached willow branches.

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Lesser snow goose populations had quadrupled since the 1970s. So many geese were arriving at their summer breeding grounds that they were eating not just plant shoots, but roots as well.
The non-interventionist camp argued that goose numbers would naturally return to an equilibrium once the food ran out. But others feared that continued overgrazing would irrevocably damage the ecosystem. Humans had to intervene, they said.

The interventionists prevailed and, 10 years ago, wildlife agencies ratcheted up hunting pressure. Now they are unsure if the increased culling is working. Further deterioration of an already degraded landscape appears to have halted, but the marshes haven’t begun to recover. Unsure what else they can do, they have adopted a wait-and-see approach for now. Here’s the problem: Further population control, which would probably mean some sort of mass extermination, is as technically difficult as it is ethically questionable.

“Large-scale elimination of birds in concentration – that would be an unprecedented move,” says Dale Humburg, chief biologist of Ducks Unlimited in Memphis, Tenn., a conservation and hunting group.

“Here you’re dealing with things that are ethically at the crossroads.”

Saltwater marshes, like those where the geese summer, are among the most productive and diverse ecosystems on earth. They’re also rare, occurring only along coasts. For this reason, scientists are particularly concerned about the northern marshes. The transformation of these productive ecosystems into mud flats hurts not only geese, but also a suite of species that lives there. In degraded marshes scientists find fewer bugs, for example, which other birds feed on. They find fewer other birds, like the normally hardy Savannah Sparrow.

“If you can damage or impact a really robust species” like the Savannah Sparrow, says Robert Rockwell, a biology professor at City College of New York who has studied the geese for 40 years, “you can only imagine what’s happening to the most delicate species.”

In times past, the lesser snow goose wintered in marshes along the Gulf of Mexico. (The greater snow goose, whose population has also risen in recent decades, winters along the US East Coast and breeds in Canada’s High Arctic.) When scientists looked into the population explosion since the ‘70s, they noted that goose numbers had risen in lockstep with the increased agricultural output of rice, corn, and wheat across the US Midwest. Where their numbers were once limited by the winter food supply, now they weren’t. The birds were reaping the benefits of increased farm production and the government subsidies that had boosted it. For scientists, the shift in feeding behavior revealed how adaptable the geese were. They had moved from marshes, which were disappearing, to expanding rice paddies and cornfields.

“We used to characterize these things as narrowly defined niche preferences,” says Ken Abraham, a waterfowl and wetlands scientist with the Ontario Ministry of Natural Resources in Peterborough. Snow geese “have broken every rule.”