This is my penultimate column for the Philadelphia Inquirer. It will run in print on Monday. The final one runs the following Monday: A century ago, Americans so vehemently hated the wolves of their Western states that they attacked them with germ warfare.
Veterinarians deliberately infected coyotes with a disease called
mange, hoping it would spread to the wolves, which it did, causing many
of them to lose so much fur that they froze to death in the harsh
winters. Now, according to a recent study by Penn State researchers, the mange survived in other animals long after the wolves were gone.
And it has resurfaced in wolf packs reintroduced to Yellowstone
National Park in the 1990s. Those wolves are also losing cubs to canine
distemper and a disease called parvovirus. These diseases struck the wolves much faster than scientists
expected, said Penn State ecologist Peter Hudson, who is a coauthor on
the study, published in the September issue of the Philosophical
Transactions of the Royal Society B. But he still expects the wolves to
pull through in the long run. “Healthy ecosystems are full of parasites,” he said. The reintroduced
wolves had no natural immunity to these diseases, but eventually he
thinks the disease organisms and the wolves will strike a balance. By tracking the way these outbreaks are spreading among the
reintroduced wolves, he and his colleagues hope to learn lessons they
can apply to understanding the dynamics of other emerging diseases.
“People used to think parasites and pathogens were of no importance
to ecology,” he said. Now, scientists are realizing the pathogens are
part of the environment and can cause animal populations to go through
big oscillations. One thriving wolf pack, called the Druids, was hit with mange in 2009
and died out the next year, said Penn State ecologist Emily Almberg,
who was lead author on the paper. But overall, the impact of the wolves continues to be dramatic. Since
their reintroduction, she said, exploding populations of elk have
declined, allowing some plants to rebound, along with animal species
that depended on them.
No one knows exactly how many wolves lived in the region that became
Yellowstone National Park before the late 1800s, when humans wiped them
out. The wolves were exterminated in a massive, government-led campaign
that employed a combination of shooting, germ warfare, and poison.
By the 1940s, wildlife conservation pioneer Aldo Leopold first
suggested that wolves played a role in the ecology and should be
reintroduced, said Daniel Stahler, a biologist with the Yellowstone Wolf
Project and the Yellowstone Center for Resources.
There was tremendous resistance from ranchers, who feared wolves
would leave the park and kill their cattle. Meanwhile, elk populations
were exploding. Finally, in 1995 and 1996, 41 wolves were brought down from Canada
and released into the park, said Stahler. By 2003, they reached a peak
of 170. Now, they are down to 100, and Stahler agrees with the Penn
State researchers that the numbers are likely to fluctuate but not
The elk population has dropped from 20,000 in the mid-1990s to 8,000
today, he said. Scientists don’t know for sure whether the drop is
entirely caused by wolf predation or also by other factors such as
drought, which affects the plants the elk depend upon for food. The decline in wolves may also reflect a rebalancing of the
ecosystem. Wolves are territorial; their leading cause of death is being
killed by another wolf in territorial disputes.
While the wolves have eaten enough elk to reduce their numbers, they
have also changed the elks’ behavior, said Penn State’s Almberg. The
wolves keep the elk on the move, “so they can’t keep hammering at one
willow or aspen stand” and destroying it. Meanwhile, ecologists have seen a cascade effect on the landscape,
with more willow and aspen surviving, which in turn benefits warblers,
beavers, and other animals that depend on those trees.
Scavengers such as ravens and grizzly bears also benefit — from the carcasses left by wolf kills.
The researchers saw the first mange cases in 2002, said Almberg, and the first outbreaks of canine distemper in 2005. Distemper, she said, is a highly contagious viral disease that
affects the nervous system and kills some adults and most wolf pups.
Mange is a skin disease caused by mites, and while it’s not fatal by
itself, infected wolves can bite and scratch themselves so much that
they die from secondary infections. Or they can lose so much fur that
they freeze to death. The outbreak, she said, went through most of the
park by 2007.
In the future, she and Hudson are calling on locals and tourists to
become citizen scientists send them pictures they take of the wolves.
“Visitor photographs are really helpful.<TH>… So many people are
out there every day taking photos,” she said. “There’s no way our staff
could re-create that field effort.”