UBC zoologist Charles Krebs has just completed the most ambitious,
ecological stakeout ever.
The life and death cycle of snowshoe hares in Canada’s North has
been observed for close to 200 years but remains one of nature’s
enduring mysteries. In regular 10-year intervals, hares from Alaska
to Labrador die in startling numbers. Populations can plummet from
100 animals per square kilometre to one.
From 1986 until last September, Krebs and colleagues have been
monitoring virtually all hare movement in sections of Yukon spruce
forest. The dogged team of technicians and researchers compiled
an exhaustive, daily chronicle of hare interactions including what
they eat, how they forage, defecate, mate and, most especially,
how they interact with predators.
“There is no doubt that predation causes mass paranoia among these
hares who are constantly looking over their shoulders during the
declining phase of each cycle,” says Krebs.
Chronic stress caused by predation is the subject of one of the
more than 103 publications and theses produced by the multimillion-dollar
project funded by the Natural Sciences and Engineering Research
Council (NSERC).
The team tested theories about the hare population cycle by sectioning
off two, square-kilometre blocks of wilderness with electrical fencing
to keep out lynx, coyotes and other mammal predators. The idea was
to observe the effects on hares of reduced predation and additional
food, both by themselves and in combination.
Results from the project showed that while both food and predation
play a role in generating hare cycles, they alone are not the root
causes. The combined treatment of predator exclusion and additional
food supplies delayed the decline but did not prevent it.
Owls and other raptors are part of the reason since they cause
40 per cent of predation and the enclosures failed to eliminate
them. Attempts to string up fishing line and nets to ward off birds
of prey were ineffective due to snow buildup.
The study also refutes a previously held theory that food shortage
followed by predation gives rise to the cycle. Krebs asserts the
phenomenon results from a complex, three-level interaction among
herbivores (hares), predators and food.
To collect their data, researchers trapped and attached radio collars
to about 300 hares and predators and monitored their whereabouts
each day. The team found that almost all snowshoe hares in the study
area died from predator attack. From 1989 to 1993, predation accounted
for 83 per cent of deaths among radio-collared hares and only nine
per cent were attributed to starvation.
Krebs’ team, including Tony Sinclair, Jamie Smith, Roy Turkington,
and Kathy Martin from UBC, and three others drawn from the universities
of Alberta and Toronto, worked from a research campsite on the boundary
of Kluane National Park.
Situated 150 kilometres west of Whitehorse in the midst of virgin
spruce forest, Krebs says the project was as much a test of human
dynamics as those of the animals they were observing.
“It is a great achievement for those involved to have sustained
that level of data collection over such a prolonged period in such
a remote location,” says Krebs. “It’s certainly a benchmark for
future large-scale research projects.”
Krebs is presently using a Killam Research Fellowship to write
up the research team findings in a publication tentatively titled,
Vertebrate Community Dynamics in the Yukon Boreal Forest.
Some other animals examined as part of the decade-long project
were lynx, coyotes, red squirrels, arctic ground squirrels, goshawks,
great horned owls, ptarmigan, spruce grouse and red-tailed hawks.
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