August 1, 2005

Loss of wolves changes Canadian ecosystem – study

By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - The loss of once-plentiful wolves in
a part of Canada's west allowed the elk population to mushroom,
pushing out beavers and songbirds and showing the importance of
top predators, Canadian researchers said on Monday.

Although scientists have long noted that the loss of even
one species can have profound effects, the report is one of the
first large-scale studies to show clearly the widespread
consequences of losing a predator at the top of the food chain.

Mark Hebblewhite of the University of Alberta, and
colleagues studied what happened in "a serendipitous natural
experiment" when wolves returned to part of the Bow Valley of
Banff National Park in Alberta.

Wolves were driven out in the 1960s "because that's what we
did then," Hebblewhite said.

"The first wolf pack recolonized the Bow Valley of Banff
National Park in 1986. High human activity partially excluded
wolves from one area of the Bow Valley, whereas wolves made
full use of an adjacent area," the researchers wrote in their
report, published in the journal Ecology.

Willow trees, river-loving birds called willow warblers and
American redstarts, and beaver dams once were common in Bow
Valley and surrounding areas. But in the areas where wolves
remained scarce and elk populations mushroomed, these plants
and animals were less common.

The wolves clearly had a major effect on elk. Elk
populations were 10 times as high in areas where there were no
wolves, Hebblewhite's team found.

This meant that elk could be found in suburban backyards,
and sometimes on hiking trails.

"Seven people are sent to hospitals every year on average
by getting into a fight with an elk," he said. "They are 250 kg
(550 pounds) on average so you don't want to get into a fight
with one. But being a park they couldn't just go willy-nilly
shooting elk and as a society we have advanced beyond wildlife
management by just shooting things."

The elk browsed on tender young willows, leaving little for
beavers and willow-dwelling birds. Aspen trees seemed less

"We also found that as elk populations climbed, active
beaver lodges declined, probably because beavers could no
longer find sufficient trees with which to build their dams,"
Hebblewhite said in a statement.

But in the parts of the park where wolves returned, the elk
populations in affected areas fell and willows were coming

While other predators such as grizzlies might have played a
role, Hebblewhite's team noted, bears were never completely
driven from the park while wolves were.

"Yes, wolves are ecologically important. It (the study)
bolsters the importance of conserving species like wolves and
other top carnivores," Hebblewhite said.