The squirrels of Mile 1044 on the Alaska Highway have kept scientists and graduate students hopping for more than 20 years. The Kluane Red Squirrel Project is continually generating intriguing, sometimes headline-making, data about ecology, evolution and behaviour.
One story about red squirrels almost inevitably leads into another. A journalist may start out attempting to explore one particular observatory-related academic paper about Tamiascurus hudsonicus but will quickly become immersed in the details of other major discoveries about the small mammals.
In this case, a pursuit of the story behind Linking Intraspecific Variation in Territory Size, Cone Supply, and Survival of North American Red Squirrels (in the Journal of Mammalogy) quickly yielded Density
Triggers Maternal Hormones that Increase Adaptive Offspring Growth in a Wild Mammal (Science Magazine/Science Express).
“The reason we became involved in studying red squirrels from the beginning was our interest in characteristics that individuals have that make them special squirrels relative to other squirrels,” says Stan Boutin, a biological sciences professor with the University of Alberta. Boutin has been involved with the project since its beginning in the late 1980s.
Squirrels are not endangered, nor are they a significant indicator species in times of troubling environmental issues, Boutin says. They are, however, diurnal; they keep busy during the daytime. They do not hibernate in winter. And they are relatively short lived. A student can observe an individual’s birth, growth, mating and ultimate fate over two or three years, or about the time period of their graduate studies.
Those interested in evolution, who need to observe changes from generation to generation, want a species whose lifespan, mating and birth cycles are quite short. And squirrel science is economical, much less expensive than keeping tabs of big creatures like bears and moose, says Boutin.
“The way we operate is that we have a series of grids. They are all mapped out. We try to mark all the squirrels that live in that area of real estate and know where they live and where their middens are located. We trap all of the individuals regularly, in particular the females, to track carefully when they get pregnant and when they drop their babies. We’ll put a collar on the female, follow her to her nest, climb up into the tree and get those babies enumerated and weighed.”
In two or three weeks, when the pups have grown some, the scientists return and affix colour-coded, numbered ear tags to them and then keep them under observation.
“So we gather all that data in a very consistent fashion every year out there. Then grad students come into the system with projects they like to pursue.”
And that, says Boutin, is a great strength of the squirrel project. There’s lots of overall long-term data to refer to when conducting other experiments of a subset of animals.
That data helps prevent jumping to seemingly obvious conclusions. For instance, in the research that led to Linking Intraspecific Variation in Territory Size, Cone Supply, and Survival of North American Red
Squirrels, a simple and basic question was asked. If an animal has more spruce cones available in its cache, is it more likely to survive the winter than one with fewer cones?
Elementary? “To our surprise the correlation wasn’t very good,” says Boutin. “The only big differences that we found were that youngsters, the young of the year that were setting up their own territories, tended to have smaller territories than any of the adults in the system and fewer cones in the midden.”
Young squirrels have it rough overall. They make up the majority of the 50 per cent of squirrels that don’t survive through a year. The average lifespan for a red squirrel is two to three years and females produce two or three young a year. A very few make it through six or seven years.
by Erling Friis-Baastad
About a decade ago, it appeared that climate change was having an impact on squirrel mating patterns, in part because of fluctuations of cone supply. The media broke the story but then, after another decade passed, further data revealed that the new mating and birthing trend was reversing.
“I’ve always advocated, you let the data speak for itself… you don’t want to build up a story and then stick to that story, (if the facts change.) As long as you have good solid data I have no problem with people changing their minds because the data tells them different.”
Access to long-term data recently led to another exciting series of experiments. Ben Dantzer, then a graduate student from Michigan, devised ways of determining how females can be proactive when educating their pups to survive in the face of competition.
“What we know is the growth rate of kids produced by these various mothers can be highly variable. Sometimes they grow rapidly. Sometimes they grow a bit more slowly,” says Boutin. The conditions they meet after leaving their parents vary with the density of cone crops. An especially bountiful cone year, a mast year, is followed by a bumper year of babies and every piece of real estate becomes chocker block full of squirrels.
The young squirrels face more competition. Their moms respond to the increasing din of territorial chatter by generating more stress hormones. They become more demanding when teaching survival skills to their young. Those young perform more effectively than other generations, those not raised in such crowded conditions by demanding moms.
“The final experiment gave females little bits of peanut butter laced with the hormone and lo and behold those females that got the extra jolt of hormone had their kids grow more rapidly.”
Without enough baseline data, common sense might lead an observer astray. Most people would think that stressed mothers would be more likely to have babies that performed poorly, says Boutin.
For more on red squirrel parenting skills, read Squirrel Scientists Tackle The Adoption Conundrum, in the Your Yukon archives for August 13, 2010. For more information on the Kluane Red Squirrel Project go to www.redsquirrel.ca/KRSP/Home.html
This column is co-ordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at www.yukoncollege.yk.ca/research/publications/newsletters_articles