"South Dakota was, until last year, east of what was called the plague line," said Dean Biggins, a biologist with the U.S. Geological Survey.
"After plague arrived in California in 1900, it spread east. By 1950 it got to the eastern border of Wyoming and stopped."
Why the disease may be on the march again is not known, Biggins says, but it's likely due to environmental factors.
What is known is that both prairie dogs and ferrets are highly susceptible to plague and succumb quickly.
Reintroduction efforts west of the plague line have not been very successful. In one case, at Fort Belknap Indian Reservation in Montana, plague wiped out both prairie dogs and ferrets completely.
Search for Solutions
Scientists are scrambling to create a long-term solution to save the black-footed ferrets, which are the only ferret species native to North America.
Travis Livieri, a biologist who works with the ferrets and prairie dogs at Conata, has begun vaccinating young ferrets against plague.
"[A vaccine] just became available, and we don't know how well it works in the wild," said Livieri, executive director of the nonprofit Prairie Wildlife Research in Wall, South Dakota.
"There is also one for prairie dogs, but we don't know how to deliver it to them yet."
Michael Lockhart, who heads the FWS ferret recovery program, added that the federal government is trying to find new release sites even farther east of the plague line. But it will be some time before those plans are finalized.
Without a more permanent solution, the biologists who watch over the ferrets are playing a waiting game. It is possible that plague, which surfaces in some years and not in others, may not return.
Another hope is that a dusting of insecticides done at the colony last year to kill fleas may protect the ferrets should the disease return.
At the first sign of an outbreakdead prairie dogs being the best indicatorthe ferrets may have to be rescued.
"If we see plague, we will probably start catching ferrets," said FWS's Lockhart, adding that some of the animals can be sent to live at two other release sites in South Dakota.
But that would only be another short-term solution, because the prairie dog colonies there are small and can't support too many more ferrets.
"It is pretty dire," Lockhart added. "We had hoped to have 1,500 breeding adults in the wild by 2010, and that is looking less and less likely."
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