Coyotes eat snowshoe hares. Lynx eat snowshoe hares. The hares breed and breed and breed until their numbers skyrocket, and then their population crashes. A year later the numbers of lynx and coyotes also plummet, and about every ten years this cycle repeats itself, again and again.

That abbreviated description only hints at the links between snowshoe hares and their two main predators. For centuries people have known that hare populations go through spectacular cycles, sometimes increasing as much as 300 fold over the span of a cycle. Lynx and coyotes also increase in number before their populations crash, but not nearly as much as hares.

This phenomenon occurs across the boreal forest, but no one agreed on what caused these highs and lows. But now, thanks to the Kluane Boreal Forest Ecoystem Project, a great deal is known about these cycles, and about other animals and plants in the Kluane area.

This massive project studied the interaction between different animals and the food they eat in a 350-sq. km. area near Kluane Lake. For ten years, up to 40 people worked on the project each summer, with a crew of about ten continuing through the winter.

Altogether more than 150 person years were dedicated to studying this patch of boreal forest, making it arguably the most well-studied ecosystem on Canadian soil. Mark O'Donoghue, who worked with the project for eight years, said that the researchers investigated a number of different theories on what drives the hare cycle.

One was that the hares eat themselves out of house and home, and become so weakened by starvation that predators are able to kill more of them. Another theory was that the number of predators in the ecosystem determined the number of hares. Other research indicated that plants played a key role, perhaps protecting themselves by producing a chemical that made them taste bad to hares.

Their various experiments pointed to the essential role of predators in causing the cycle, and at Kluane, they had a prime opportunity to look at two very different types of meat-eaters. O'Donoghue describes coyotes as the "prototype generalists" while lynx are the "prototype specialists."

Coyotes have expanded across the continent from their original range on the North American Prairies, arriving in the Kluane area around 1910-20. With their relatively small feet, they are not well-adapted to hunting in soft deep snow.

Lynx, with their large paws and long legs, are beautifully designed for hunting snowshoe hares. The two animals have almost exactly the same geographic ranges, and it was always assumed that lynx were completely dependent on their favourite prey.

Figuring out how an ecosystem works, especially one with predators that cover as much ground as lynx and coyotes, is no easy task. In Kluane the answer was to spend lots of time out on the land, gathering as much information as possible.

Researchers put 12,000 kilometres on their snowmobiles and 4,500 kilometres on their snowshoes looking for tracks and kill sites. They poked through kill sites to see whether the predators were eating every last bit of their prey, and analyzed their scats.

Every day they would drive the Alaska Highway in a truck mounted with a radio receiver, keeping track of the radio-collared hares. When a change in the radio signal indicated that a hare was dead, they would go and find the carcass to see which predator had killed it.

It was a phenomenally labour intensive effort, but it paid off with reams of data and many interesting conclusions. For one they found that this far north, the definitions of generalists and specialists are not always cut and dried.

It's usually assumed that specialists will have a greater impact than generalists on the numbers of prey because specialists have only one main item on their menus. But that is not exactly what they found in the Kluane area.

When hares are less plentiful, coyotes hunt more voles while lynx switch to hunting red squirrels. It takes six red squirrels to equal the amount of energy provided by one hare, so the biologists had assumed that lynx would switch back to hunting hares as soon as their numbers started to rebound.

To their surprise, the "generalist" coyotes switched back to hares more quickly than lynx, the "specialists." The lynx continued hunting red squirrels even when there were more hares back in the woods.

"It puts a different twist on the specialist/generalist contrast," says O'Donoghue. "In this area, coyote are not as good at killing other prey, so locally at least coyotes act as more of a specialist than the lynx."

There were other surprising results. For example, they learned that both of these predators will kill more hares than they need to survive. Also, they increase their kill rates at different points in the cycle. Lynx kill more hares as the hare populations are declining, while coyotes kill more as the hare population is increasing.

They discovered that coyotes do three-quarters of their killing early in winter when there is less snow. Then they cache the extra carcasses and eat them as needed. The large-pawed lynx usually just eat their prey right away, knowing that deeper snow will not affect their hunting success.

All of these findings point to the huge impact that predation has on the hare cycle. But even with all of the work that has been focussed on Kluane, many questions remain. For example, it's not known why the number of hares stays low for so long, even after the number of predators has dropped, or why this cycle occurs at the same time across North America.

But one thing is for sure. Right now, all across the boreal forest, there are a lot of bunnies in the woods. The last hare cycle peaked in 1990, so these small animals are approaching another high, to be followed by the inevitable crash.

O'Donoghue is writing a chapter on coyotes and lynx for a book that is being written on the Kluane Boreal Forest Ecosystem Project. Now a regional biologist in Mayo, he can be reached at the Renewable Resources office there at 996-2162.