Some smart squirrels are turning the law of cause-and-effect on its ear in the Kluane region.
Whereas most animals respond to changes in their environment after the fact, the red squirrel has shown it can predict when its food source will be plentiful and ramp up its reproduction to be ready for the windfall.
“It was a great surprise to us,” said University of Alberta professor Stan Boutin, who has studied the species in the Yukon’s Kluane region for more than 15 years.
The study’s findings were published in the December edition of the journal Science.
Boutin and his research team began exploring how animals cope with changes in their environments and the red squirrel was the researchers’ perfect guinea pig.
The squirrel’s young are easy to find and tag.
The animals are highly territorial, making them easy to track.
They have fairly simple food requirements — preferring to munch on seeds from white spruce trees.
And, because white spruce don’t produce consistent seed crops from year to year, they were the perfect species to use to study the effects of food fluctuations.
“It was a really nice model to work with and that’s how we got started,” said Boutin.
Each year, for 15 years, researchers returned to the same study area and marked the animals by live-trapping them and tagging their ears.
The researchers recorded where the critters live and their reproductive habits — like litter size and mortality rates.
They also counted and recorded the number of cones produced by the spruce trees.
The first big cone-producing year came in 1993, and that was when the scientists got their big surprise.
“Lo and behold — in 1993 we saw females producing bigger litters and some were producing a second litter for the very first time,” said Boutin from Edmonton.
Researchers didn’t see another big crop until 1998, and the same thing happened.
“We were just run off our feet trying to keep track of all the youngsters produced in that year,” said Boutin.
With the phenomenon occurring consistently, Boutin began formulating a theory.
“There’s a mismatch in what the ecology of the system predicts should happen and what the evolution of the situation predicts.”
The squirrels produce the big litters before the cones are available to them, and when their resource levels are really low.
They’re taking a gamble that the food necessary to sustain the youngsters will be there when it’s needed.
And, so far, that gamble has paid off.
In fact, they do much better than females that produce the youngsters after the cones were produced, said Boutin.
“Then the world would be full of squirrels who would have their resources decline over time.”
So how do the wise females know when to mate?
“It’s dead obvious they have a good cue because they don’t make mistakes,” said Boutin.
Researchers don’t know what that cue is, but they speculate it’s probably tied to the buds that become the cones on the tree.
The spruce tree produces two types of buds that are indistinguishable by sight — one turns into cones, the other into more tree branches.
Squirrels munch on both through the winter months.
So researchers speculate that when the squirrels ingest more cone buds the hormones in the food kick-start their own hormone production.
“It may be that they’re inadvertently being turned on by consuming these buds.”
But that’s just speculation right now, said Boutin, who plans to continue the research.
“This really falls into the category of ‘neat to know’ information,” said Boutin.
It’s like playing the stock market, he said.
“If we had a fabulous cue to predict when the stocks were going to explode, the people that got in early would do extremely well.
“But most of us don’t have that cue so we tend to follow the stock market and invest when things are looking rosy.
“As a consequence we never do as well as we could have done if we had this predictive cue like the squirrels have,” he said.