Hare Today, Squirrel Tomorrow
Life is hard for snowshoe hares. They live in a tough country---ours. These big-footed bunnies are found where winters are harsh. They eat tough food, preferring certain types of woody plants. The plants fight back; heavily browsed willows and birches apparently crank out hare-sickening chemicals in defense.
Even more hazardous than severe weather and cantankerous food are the hares' predatory neighbors. Lynx are so fond of hare diets that the big cats' populations closely follow the years-long cyclical surge and decline of hare numbers, but weasels, martens, foxes, wolves, coyotes, owls, hawks, and just about every other predator in the north also happily hunt hares.
Assessing the role of predators in the hares' population cycles was the crux of some research that began in 1989 near Kluane Lake in the Yukon Territory. As part of the Kluane Boreal Forest Ecosystem Project, the husband and wife team of Mark O'Donoghue and Susan Stuart studied the ecology of juvenile snowshoe hares.
The change in numbers of snowshoe hares from trough to peak of their eight- to eleven- year cycles can be dramatic. Where one adult hare might be found in a 200-acre plot at minimum, as many as four might crowd onto a single acre at maximum. Studies in Canada and the contiguous northern U.S. show that the survival rate of juveniles is the most important factor affecting the increase (or decrease) of hares during the cycle. A good number of the youngsters had to fall to predators, but no one had studied how many very young hares---those less than a month old---were eaten. O'Donoghue and Stuart decided to concentrate on the infant hares, paying special attention to how many of them were caught and eaten.
Newborn hares are precocious. Their eyes are opened within an hour of birth, and they can hop fast enough to challenge a field scientist by the time they are a day old. Nevertheless, the researchers affixed tiny radio transmitters to many baby hares, and put identifying ear tags on 850 of the newborns.
The scientists observed that the youngsters get little of their mother's time. A litter stays together less than a week. After that, each baby picks its own hiding places. It joins littermates for about ten minutes of milk and motherly attention once a day. Slowly the young hares range farther afield in their search for hideouts. They begin to browse on soft plants within two weeks, and will be fending for themselves by the time they are a month old---a good thing, because their mother's next litter will arrive 36 days after their birth.
Even with the mother's great caution not to lead predators to the litters, and with the infants' own skills at hiding (and soon hopping away), 170 of the tagged hares were lost to predators before they had lived 10 days. This carnage did not surprise the scientists. They knew that a baby hare in a forest has about the same life expectancy as a chocolate-chip cookie in a schoolyard, and for about the same reasons.
What did surprise them was what killed the dead juveniles. They found 80 of the victims stashed in trees or in red squirrel middens. Since squirrels are known to eat carrion, they assumed scavenging squirrels had collected the carcasses of hares killed by other predators.
But they could think of no predator that would leave so much for squirrels to scavenge. And the number of stashed dead juvenile hares kept mounting and mounting.
Then they observed a red squirrel attack and kill a baby hare. Other biologists working at Kluane saw similar attacks, some successful, some not. The squirrels were providing the corpses, not just storing them.
After two summers of work, O'Donoghue and Stuart concluded that squirrels are the chief predators of hares less than two weeks old. In fact, squirrels killed and eventually ate nearly half of the snowshoe hares born at Kluane.
If they had a vote, I'11 bet hares would call for aerial squirrel control.
