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The secret life of red squirrels

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Posted: Sunday, January 27, 2013 12:00 am

FAIRBANKS — About a decade ago, I wrote about Canadian biologists who found that red squirrels in the Yukon seem to be evolving to give birth earlier. During their 10-year study, 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 main researcher on a red squirrel project that has revealed much about the biology of one of the North’s most visible mammals. He and his coworkers, such as Andrew McAdam of the University of Guelph, have gotten to know all of the more than 200 red squirrels in a one-kilometer-square patch of boreal forest between Haines Junction and Kluane Lake.

The oldest red squirrel they found in their study area lived to an age of nine. Most squirrels reached three or four years before they disappeared, either becoming a meal for a goshawk, owl or a larger mammal, such as a lynx. From their birth in March, 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 would 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 “bequeathal.” Another habit exclusive to breeding mothers was the takeover and defense of a second midden in the fall, which the mother would then give to a pup the following year.

“That’d be like you putting away money for your future offspring to go to university,” Boutin said.

Since the researchers know each of the red squirrels on their plot, which borders the Alaska Highway, the scientists have been able to find family connections between squirrels, such as the sister visits on cold nights.

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

Boutin has also observed red squirrel adoption. After the death of a mother squirrel after it had given birth to pups, the dead squirrel’s relatives took in one of the youngsters as their 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 20 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.

Since the late 1970s, the University of Alaska Fairbanks' Geophysical Institute has provided this column free in cooperation with the UAF research community. Ned Rozell is a science writer for the Geophysical Institute. This column first appeared in 2003.

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