Climate Snuffing Isle Royale Moose, Wolves

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“Moose were dropping dead of starvation right in front of park visitors.”
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Washington Post
July 21, 2008

Warming Alters Predator-Prey Balance
By Kari Lydersen
ISLE ROYALE, Mich. — For six decades since they
loped across frozen Lake Superior to reach this
rocky island, wolves have roamed 45-mile-long
Isle Royale, the nation’s least-visited national
park.

The wolves survived the extermination efforts by
the island’s few inhabitants, who in the 1950s
and ’60s saw them as mortal enemies. And they
survived an outbreak of deadly canine parvovirus
in the 1980s. Now, scientists tracking the wolves
in the world’s longest-running “single
predator-single prey” study fear that the Isle
Royale wolves could become extinct because of
global warming.

Next weekend, scientists and National Park
Service officials from around the country will
celebrate the 50th anniversary of the Isle Royale
Wolf/Moose Study, which has helped reveal how
predator-prey interactions can affect entire
ecosystems. Because the two species live in
geographic isolation here in the largest of the
Great Lakes, with no other predators or prey and
minimal interference from humans, it is an ideal
laboratory in which to study how their fates are
intertwined.

But the anniversary may not be a happy one, as
both populations are close to their lowest-ever
levels and have been feeling the effects of
Earth’s rising temperatures.

When moose are plentiful, the wolves also thrive,
hunting as a pack and often tracking moose for
days before making a kill. If the moose
population drops — from disease, starvation or
tick infestation — the wolves also suffer. When
the wolf population plummeted from a high of 50
to a low of 14 in the early 1980s because of
parvovirus, moose numbers rose. And when the
severe winter of 1996 caused moose to starve, the
wolves gorged on the carcasses and easily picked
off weak, underfed moose.

Since the study was begun by Purdue University
professor Durward Allen in 1958, it has tracked
many such ups and downs. But scientists fear that
the forces that drove those fluctuations are
paling, compared with the impact of climate
change on the island’s ecology.

Researchers monitor both populations by plane
overflights early in the year. This spring, they
counted 23 wolves and about 650 moose, down
sharply from the highs of 50 wolves in 1980 and
almost 2,500 moose in 1995. In 2006, moose
numbers hit a record low of 385.

With the exception so far of this year, summers
over the last decade have been unseasonably warm
on Isle Royale. Moose thrive in frigid boreal
climates, but when the mercury rises above 60
degrees Fahrenheit, their heart and respiration
rates increase, and every step is an effort. They
spend warm days resting or submerged in water
rather than eating the 40 pounds of vegetation a
day they need to fatten up for the winter, when
the only food sources are twigs and fir trees.

A hot summer means weaker and older moose may die
from heat stress. Come next winter and spring,
many others will starve because they ate too
little during summer. Or they will be so weak,
they will be easy prey for the wolves.

“It all started in 1998,” said study director
Rolf Peterson, a research professor at Michigan
Technological University. “Moose were dropping
dead of starvation right in front of park
visitors.”

The heat also encourages ticks that make moose
miserable. Later onset of winter means more time
for the blood-sucking ticks to latch onto a
moose, and earlier springs mean more success for
tick eggs.

Over the winter, a tick-infested moose may need
to replace 100 percent of its blood. They also
rub, bite and scratch off their hair in an effort
to rid themselves of the insects. This spring,
said study co-director John Vucetich, the average
moose had lost 75 percent of its hair, and one in
four had lost 95 percent.

“There were bare-naked moose running around,” he said.

No one thinks the moose, which arrived on Isle
Royale about 100 years ago by swimming from the
mainland, will disappear. But with fewer moose,
the wolves could be doomed. Desperate wolves have
been seen chomping on old moose bones and even
eating green apples from trees.

Peterson, who lives with his wife in a fishing
cabin on Isle Royale surrounded by hundreds of
antlered moose skulls, said the wolves are still
suffering from the moose crash of 1996.

“Now wolves are living on moose born in the early
1990s, before the collapse,” he said. “It’s like
they’re feeding on a baby boom generation that’s
not backed up.”

Vucetich noted that climate change can have
contradictory effects. Milder winters and earlier
springs mean more food for moose, while winters
with deep, crusty snow benefit the predators,
which can walk atop the snow while the moose
crash through. Less snow gives the moose an
advantage.

But ultimately, Vucetich said, “moose are
creatures of the north country who like it cold.
If it gets warmer, they won’t fare well.”

It’s worse for the wolves. “Wolves will go
extinct before moose do, and their extinction
could definitely be caused by climate change,”
Vucetich said.

In 1978, gray wolves of the type found on Isle
Royale were listed as an endangered species in
all the Lower 48 states except Minnesota, where
they were labeled threatened. Wolf-recovery
programs around the country had solid success
over the next few decades, and in 2007, the
western Great Lakes wolves were delisted,
although legal wrangling over their status
continues. There has also been debate over the
years about the fate of the wolf-moose study,
which is financed by the National Park Service,
the National Science Foundation and others.

Vucetich conceded that the survival of about 20
wolves on an isolated island visited by
relatively few people may seem like a
less-than-urgent issue. But he sees larger
symbolism to the project, since it illustrates
the intricate interdependence of species.

“It is an opportunity to appreciate how
complicated this is, to generate a sense of
wonder about nature,” he said. “That’s why we
should care.”

© 2008 The Washington Post Company
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