by Wilson Ring
Hidden on hillsides in a remote part of
western Vermont, a small number of venomous timber rattlesnakes slither
among the rocks, but their isolation can't protect them from a
mysterious fungus spreading across the eastern half of the country that
threatens to wipe them out.
In less than a
decade, the fungus has been identified in at least nine Eastern states,
and although it affects a number of species, it's especially threatening
to rattlesnakes that live in small, isolated populations with little
genetic diversity, such as those found in Vermont, New Hampshire,
Massachusetts and New York.
In
Illinois the malady threatens the eastern massasauga rattlesnake, which
was a candidate for the federal endangered species list even before the
fungus appeared.
Biologists have compared its appearance to the
fungus that causes white nose syndrome in bats, which since 2006 has
killed millions of the creatures and continues to spread across North
America.
It's unclear, though, if snake fungal disease,
"ophidiomyces ophiodiicola" was brought to the United States from
elsewhere, as was white nose fungus, or if it has always been present in
the environment and for some unknown reason is now infecting snakes,
biologists say.
"I think
potentially this could overwhelm any conservation effort we could employ
to try to protect this last remaining population," said Doug Blodgett, a
biologist with the Vermont Department of Fish and Wildlife who has been
studying the state's rattlesnake population for 15 years. "We don't
have any control over it. It's just completely out there in the wild."
Rattlesnakes were once found across much of the country, but
habitat loss and efforts by fearful humans to wipe them out reduced
their numbers, especially at the northern edges of their range.
In
New Hampshire, the disease helped halve the population of rattlesnakes —
now estimated at several dozen — after it was first spotted in 2006,
although it was only afterward that scientists linked the fungus to the
decline, officials said.
Vermont's population of timber
rattlesnakes is down to two locations near Lake Champlain in the western
part of the state with an estimated total population of several
hundred.
An Associated Press reporter was allowed to accompany
wildlife officials to a rattlesnake habitat on condition the exact
location not be revealed out of concern that too much attention could
further threaten them. Blodgett led an hours-long search for some of the
elusive creatures until he found a pair hiding in a rocky crevice,
though it wasn't clear if they were infected. Later, a healthy single
snake was found on the forest floor.
The disease can cause crusty scabs and lesions, sometimes on the head.
Jeffrey Lorch, a microbiologist with the U.S. Geological
Survey's National Wildlife Health Center in Madison, Wisconsin, said
he's been getting reports of snake fungal disease from all over the
eastern United States. Not every location is reporting that the disease
is threatening snake populations.
"It does seem to be a disease that has different effects in different areas," Lorch said.
The
fungus poses a greater risk to snakes that reproduce slowly, such as
rattlesnakes, which can live up to 30 years, experts say.
In
Illinois every year the disease infects about 15 percent of the
population of about 300 of massasauga rattlesnakes, most of which are in
Clinton County, with a mortality rate of 80 to 90 percent, said Matt
Allender, a wildlife veterinarian and epidemiologist at the University
of Illinois who started noticing the fungus in 2011. The mortality rate
in infected timber rattlesnakes is estimated between 30 and 70 percent,
he said.
The fungus' impact on the massasauga is expected to play a
part in the U.S. Fish and Wildlife Service's determination on whether
to list the snake as endangered, officials said.
"I think that in
populations that have been shrunk due to other mechanisms, such as
habitat loss, other environmental changes, those types of things, are
more at risk of going extinct from snake fungal disease mainly because
it's a smaller population," Allender said. "They have less of a buffer
to withstand these diseases."
Part
of the challenge in studying the disease is that snakes, especially
venomous varieties, don't get much sympathy from the public, which makes
funding studies harder. Snakes are also harder to find than, say,
white-nose-infected bats where scientists can go into a cave and see
tens of thousands of carcasses, Lorch said.
The
fungus has been found in all five rattlesnake populations in
Massachusetts, but it doesn't appear to have had the high mortality rate
reported elsewhere, said Anne Stengle, a Ph.D. candidate at the
University of Massachusetts who is overseeing a federal grant in nine
states to study the fungus.
Since
the initial hit, the decline in the Granite State's timber rattlesnakes
appears to have stabilized and some are reproducing, said New Hampshire
Fish and Game Biologist Mike Marchand.
"I'm
at least optimistic that there are animals that are successfully
surviving from year to year as well as reproducing," Marchand said. "We
had a pretty strong dip in the population."
