The Secret Life of Red Squirrels

During a decade-long study, Canadian biologists found that red squirrels in the Yukon seem to be evolving to give birth earlier, possibly in response to a warmer climate. The scientists also discovered that sister squirrels have slumber parties on cold nights and mother squirrels plan ahead for their pups' future.

Stan Boutin, of the University of Alberta in Edmonton, is the primary researcher on a project that has revealed the biology of one of the north's most plentiful mammals. He and his coworkers, such as Andrew McAdam of the University of Alberta, know all of more than 200 red squirrels in a one-kilometer-square patch of boreal forest between Haines Junction and Kluane Lake.

The oldest red squirrel in their study area lived to an age of nine. Most squirrels reached three or four years before they disappeared, usually as a meal for a goshawk, owl, or a larger mammal, such as a lynx. From their birth in April or May until the time they die, red squirrels often spend their entire lives in a small patch of forest surrounding a midden. A midden, the center of a red squirrel's world, is a pile of spruce cones-a squirrel's winter food supply-carved with tunnels and chambers.

When squirrels sound off with a rattling call, they are signaling their possession of a territory, McAdam said. Squirrels are loners except for the day a female is in estrus during the breeding season. On all other days, it's one squirrel to a territory.

"It's a hell of a battle going on out there," Boutin said. "If you're on that spot, you have it until you die, or leave."

Boutin and McAdam aren't quite sure how squirrels determine which one takes over a new territory, but the researchers said it helps if a squirrel is large. Squirrels seem to know the squirrels around them by their calls, and they notice when the calls stop.

"When they haven't heard a call from their neighbor in awhile, they might go and see if their neighbor has bitten the dust," McAdam said.

In a world saturated with red squirrels, how does a newborn establish its own turf? Boutin noticed that mother squirrels sometimes give their pups a head start in life.

"We started seeing females that would go AWOL and leave the kid defending the territory," Boutin said. "Then the female would show up one or two territories over, where there was a vacancy."
Boutin calls that behavior, in which the mother gives up its territory to a pup, "bequeathal." Another habit exclusive to breeding mothers is the takeover and defense of a second territory in the fall, which the mother gives to a pup the following year.

"That'd be like you putting away money for your future offspring to go to a university," Boutin said.

Since the researchers know each of the red squirrels on their plot, the scientists have been able to document family bonds between squirrels, such as sister squirrel visits on cold nights.

"They know who their neighbors are, and they react differently to relatives," Boutin said. "Related females actually share nests on cold nights, then go back to their own territories when it warms up."

Boutin also has observed a red squirrel adoption. When a mother squirrel died after giving birth to pups, her sister took in one of the youngsters as her own.

Boutin chose to study red squirrels so he could monitor an entire population of mammals, and he and his crew have succeeded at that for more than 10 years. In dedicating his time to researching red squirrels, he has opened a window on the most visible small mammal of the boreal forest.

"The more we investigate into their lives, the more interesting things we discover," McAdam said.