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07/28/2004
Moving Down from the North
I have no more than a handful of memories of my childhood in
Denver, Colorado, where I was born and lived until the age of 5.
One memory is of a trip to the mountains and feeding peanuts to
the chipmunks. Ever since, I’ve thought of the chipmunk as a
cute little critter. Within the past year or two the chipmunk
population in our town seems to have exploded and a few have
chosen our yard as their abode. In fact, we’ve been waging a
battle with them over property rights to the entrances to our
kitchen and our porch. If you follow the comic strip “Over the
Hedge”, it’s much like the ongoing conflict between the humans
and the raccoon and turtle and their animal companions.
Actually, we do have a raccoon that tips over our garbage cans.
The chipmunks are tunneling under the bricks comprising our
kitchen entrance. As a result, the bricks are sinking. Chipmunks
like to dig their tunnel entrances in obscure places under stones.
A pile of dirt keeps appearing on top of the flagstone step to our
porch. We put the dirt back in the hole and the next day it’s back
again. My wife thought mothballs in the hole would stop the
activity but the dirt plus the mothballs end up on the flagstone.
After weeks of fighting a losing battle, I wasn’t surprised to read
of the work at the University of Illinois at Urbana-Champaign
that confirms the hardiness and stubbornness of the chipmunk.
The university’s Web site cites the work of graduate student
Kevin Rowe, working with Prof. Ken Paige and with Edward
Heske and Patrick Brown of the Illinois Natural History Survey.
These guys trapped 244 chipmunks, nipped off bits of tissue
from the tips of their ears and released the animals at the sites of
the trappings. They then analyzed DNA from the tissues.
When you think of the Ice Age in North America, you think of
huge sheets of ice spreading down out of Canada driving any
animals southward. As the glaciers melted back, the animals
returned northward. There were many periods of glaciation and
meltback over the past million years. The ebb and flow of the
animals being pushed southward and then returning as the
glaciers melted has been the commonly accepted scenario. My
1962 World Book Encyclopedia describes such a pattern.
Now it seems that at least one animal was an exception. The
Illinois researchers were surprised to find that the DNA samples
show that the chipmunks now living in Wisconsin and Illinois
have ancestors who survived the last North American ice age.
These sturdy contrarians stayed up north, then came down and
mixed in with other groups of chipmunks coming from the
warmer southern and eastern climes.
The researchers’ findings indicate that during the ice ages there
were patches of land, “refugia”, that were not covered with ice
but were forests with enough plant life to sustain our hardy
chipmunks. Apparently, there is now some geological evidence
that supports this conclusion. According to Prof. Paige, their
study shows that it will not be as straightforward as thought
previously to predict the movements of various animals during
the global climate changes now underway.
Back in Denver some years ago, my wife and I took a side trip to
Yellowstone and to Jackson Hole. We stayed in a cabin at
Jackson Hole Lodge for a couple of nights and I may have
written earlier of our experience with another small rodent. The
first night, we were awakened by a mouse nibbling on my wife’s
purse and spent most of the night chasing it. The mouse kept
returning to the purse. The next morning I went to the Lodge
desk and asked if they had a mousetrap. Yes, they would loan
me a trap. However, they warned that, if I killed the mouse, I
would have violated park, maybe even Federal rules against
harming a wild animal in a national park.
Fortunately, I found the hole that the mouse used to gain
entrance to our cabin and plugged it with aluminum foil. It
worked and I didn’t have to worry about being jailed for killing a
mouse! The incident brought home to me the complexity of
trying to save our environment. On that same trip, we saw in
Yellowstone the beginnings of recovery of areas that had been
burned out during a period of severe wildfires. These fires, you
may recall, stimulated much discussion and controversy about
when we should intervene to stop such fires and about the
possible benefits of controlled burns and logging. The
controversy still continues, with defenders and critics of the Bush
administration’s policies in this area.
Among the casualties of the Yellowstone fires were aspen trees,
whose yellowed leaves in the fall provide a glorious golden hue
to Western vistas. But aspens, cottonwoods and other trees have
also been in trouble in Yellowstone in areas unaffected by fire
such as the Lamar Valley. The problem is not that there aren’t
aspens and cottonwoods around. There are but they are old,
maybe 70-100 years old. Until very recently, however, there
were no young trees to replace the geriatric trees. What was the
problem and what was the solution? That’s the subject of
“Lessons from the Wolf”, an article by Jim Robbins in the June
2004 issue of Scientific American.
Photos from the early 1900s show a Lamar Valley loaded with
young aspen and willow trees. By the 1930s, there were virtually
no young trees in the valley. William Ripple of Oregon State
University was intrigued and began taking cores from the trees.
He found that none of the sampled trees grew from the 1930s to
the 1990s. Only two of the trees sampled had started to grow
after the 1920s. Ripple realized that the 1920s were when the
last of the gray wolves in Yellowstone had been killed or driven
out.
With the wolves gone, the elk needed no longer fear being eaten
and they came forth and multiplied, gulping down every young
tree that emerged from the ground. Hordes of elk stripped the
valley of vegetation. Beavers no longer had food and they
departed in the 1950s. Without the beaver ponds to encourage
the growth of succulent plants, grizzlies could no linger rely on
the succulents that furnished them sustenance when they came
out of hibernation. What to do? Bring back the wolves!
In 1995, the experiment began. Where to get the wolves? There
were wolves in neighboring Montana but these wolves were used
to preying on deer. In Canada, there were wolves that preyed on
elk. A group of 14 wolves was brought in from Canada in 1995
and another 17 in 1996. To avoid genetic problems from
inbreeding, the wolves were taken from different packs in
Canada. To keep the wolves from becoming used to humans,
they were kept away from human contact in 1-acre holding pens
for two months before being released. As of the end of last year,
the wolves had formed 16 packs with a total of 170 wolves. (An
article by John Pickrell dated December 4, 2003 on the National
Geographic Web site gives figures of 21 packs and 220 wolves in
Yellowstone and the surrounding areas at the end of 2001.)
Whatever the wolf numbers, the elk population has dropped
significantly and the remaining elk have become smarter. They
have decided that grazing in river bottoms and places where they
don’t have a panoramic view of their surroundings makes them
prime targets. They have wisely opted to move to places where
they can command better views of their surroundings and any
predators. Young trees are thriving in areas that have been
vacated by the elk. Beaver have returned and started building
their dams. The trees also help stem erosion and the woody
debris pools in the river, promoting slower flow and trout habitat.
The wolves also typically leave the elk carcasses before fully
consuming them, thus providing food for scavengers such as
coyotes, ravens, grizzlies, eagles, magpies and the like.
Songbirds are back. Obviously, the wolf has done its job well.
Or has it? A recurring theme in these columns is that there are
always skeptics and this case is no exception. Skeptics point out
that there hasn’t been a truly harsh winter since the wolves were
introduced, that the climate has been warmer and that there has
been flooding along the river. It may take years for the wolf’s
full effect to be determined but, in the meantime, I’ll consider the
experiment a big success.
Interestingly, just a couple weeks ago, Gail Norton, Secretary of
the Interior, proposed to remove the gray wolf from the
endangered list from Maine to the Dakotas. In an AP dispatch on
AOL News Steve Karnowski reports that the new regulation
would, however, maintain the “threatened” status for the gray
wolf across the West, including Yellowstone.
As for me, what to do about those pesky chipmunks?
Allen F. Bortrum
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