Isle Royale Wolves Fewer, But Thriving
HOUGHTON, MI--There are fewer wolves on Isle Royale this year than last,
but those that remain are experiencing the best of times, according to
Dr. Rolf Peterson, a Michigan Tech wildlife biologist who has directed
annual surveys of the predators for the National Park Service for the
past 31 years.
Peterson said the just completed 2001 survey showed total wolf numbers
had dropped to 19 from 29 a year ago, mostly because of inter pack warfare
and a decreased crop of moose calves born in 1999, following the hot,
dry summer of 1998.
"Mild winters like we had in 2000 may be welcomed by humans, but
they can be tough on wolves that rely on moose for their main source of
food," said Peterson. "When snow cover is light, moose can move
around easily and are much more difficult for wolves to catch and kill."
During the easy winter of 2000, wolves on Isle Royale weren't able to
kill as many moose as they needed to maintain robust health. The hot,
dry summer of 1998 made life difficult for moose because they don't perspire
like people do--instead they become overheated and hyperventilate and
have to use a lot of energy just trying to keep cool. Those same conditions
led to an increased tick infestation the following winter, which further
weakened the island's moose. The result was that probably fewer than 100
calves were born in 1999--and calves provide the most reliable prey for
wolves.
With heavy snow cover on Isle Royale this winter, wolves in the National
Park are having a much easier time. "The 2000 calf crop produced
between 200-300 animals," said Peterson. "And heavy snow makes
traveling tough for calves, so this winter wolves have the advantage and
two-thirds of all the moose kills we examined were calves.
"This is about as good as it gets for a wolf."
Peterson said the island's West Pack has been eliminated and their territory
taken over by the Middle Pack, which numbers six animals. The East Pack,
also numbering six wolves, has maintained its territory on the moose-rich
east end of the island. "And there is a third pack of just a reproducing
pair and one surviving pup that has carved out a territory for itself
on the northeast side of the park and the other packs have respected its
territory," said Peterson. "There is also another mated pair
and two single wolves wandering about the island and making do as best
they can."
He said all the wolves seen in the park this winter seemed in good health.
However, biologists plan to trap some of them later this spring to check
for diseases. No parvovirus, a deadly canine disease, has been found in
Isle Royale wolves during the past 10 years.
Peterson said the park's moose herd has increased slowly since the summer
of 1996 and now numbers about 900 animals. He said a major challenge for
moose on Isle Royale lies in the poor winter food supply, especially on
the west end of the island, where the animals often have to try to survive
on lichens. Moose on the east end fare better because of the large balsam
fir stands growing there.
The annual wolf-moose study is funded by the National Park Service, the
National Science Foundation, and Earthwatch, Inc.
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For more information, contact Rolf Peterson at 906-487-2179 or email:
ropeters@mtu.edu.
03/08/01-MTN015
Rolf Peterson
at home
on the island.