“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.