Tiny, tasty ‘ecosystem engineers’ hit tough times

Town-dwelling Yukoners might be surprised to learn that a long-time neighbour is in trouble. Doesn't the Arctic ground squirrel pop up everywhere? Its burrows extend into yards, driveways, parking lots and airports.

Erling Friis-Baastad

Town-dwelling Yukoners might be surprised to learn that a long-time neighbour is in trouble. Doesn’t the Arctic ground squirrel pop up everywhere? Its burrows extend into yards, driveways, parking lots and airports. Its alarm cries are such a common feature of the suburban summer that we readily tune them out.

“It’s very easy to come to the conclusion that they’re doing well,” says zoologist Jeff Werner. “But in reality, if you go look for them in more natural habitat, you will find they are all but gone.”

Werner, a PhD candidate at University of British Columbia, has been working near Burwash for the past two summers. He and his research team are trying to learn why these creatures, Urocitellus parryii, are disappearing from historical habitat, what the significance of that is for ecosystems and what, if anything, might be done to reverse this trend.

The ground squirrel’s decline is more than an academic conundrum for this scientist. In fact, it’s at the core of his passion for conservation. “My research has been, and always will be, motivated by a concern with the state of the world and focused on understanding why populations become imperiled,” Werner says.

The life cycles of many small mammals appear somehow related to that of the snowshoe hare. “Fifteen years ago, when the hare populations dropped so did the ground squirrels’,” he says. At that time, it was thought that this would be a natural process wherein both parties would eventually increase to former levels.” This just didn’t happen.

Big changes are afoot in the mountain boreal, he says. “The famous hare cycles are starting to break down. They are not as pronounced, not as predictable. We don’t know why.” That’s also the case with the ground squirrels. “Over the past couple years, I’ve discovered that there have been many local extinctions,” Werner says. In fact, meadows that once hosted thriving burrow complexes are now ghost towns.

There are many possible causes – combinations of factors likely working together. Perhaps it has something to do the changing makeup of predator populations. Perhaps changing weather is a factor, with winter rain events in Haines Junction drowning ground squirrels in their burrows.

Changing climate can result in a change of vegetation and possibly taller plants. Ground squirrels stand about 20-cm on their hind legs. Plants taller than that can conceal approaching predators.

Perhaps the absence of fellow ground squirrels from a region means new squirrels aren’t drawn in. One experiment being conducted near Burwash uses loudspeakers, monitored by cameras, to broadcast squirrel calls from deserted burrow complexes eight hours a day. Will a perceived presence of squirrels attract new settlers?

“Typically, low population densities can be difficult to recover,” says Werner. “This is a theoretical concept and hard to identify in nature. But all over the world we have seen there are critical densities, threshold population sizes, below which population recovery is unlikely. It’s almost like a switch has been flicked.”

Werner can now walk through great burrow complexes that were constructed over centuries. These are now collapsing in a matter of decades because there are no local squirrels to maintain and expand them.

This isn’t bad news only for Arctic ground squirrels. Not surprisingly, they provide food for a myriad of animals. In April, when the first squirrels poke their sleepy heads above ground, larger creatures – bears, coyotes, foxes, lynx and hawks – will also have endured long winters and are counting on the food source. As well, humans have traditionally relied on ground squirrels for food and sometimes for outerwear such as hats and coats. These are among the reasons the Kluane First Nation has encouraged Werner’s work.

“And it’s also interesting from a larger perspective. We know that ground squirrels have a huge effect on the landscape around them,” says Werner. In 1971 Portland State University geomorphologist Larry W. Price wrote that ground squirrels displaced so much soil through digging “that they actually influenced the shape of entire valleys.” Some folks now call them “ecosystem engineers.”

People are also taking more interest in the influence these small herbivores have on plant diversity, says Werner. Without ground squirrels on hand to limit more aggressive plants, other species might die out – depriving herbivores of nutrition sources.

Werner’s research is not only a matter of passive observation. He is reintroducing the ground squirrels to areas they’ve abandoned. “I’m hoping especially to understand whether these habitats, which formerly supported healthy populations, have changed in some way that they don’t or can’t or, sometime in the future, won’t support ground squirrels.”

Werner has been given permission to live trap ground squirrels from more-urban areas where they are still apparently thriving and transport them to regions where they’ve vanished. They’re given radio collars so their activities can be tracked.

Werner’s team has set aside a rectangle of meadow, of about one by six kilometres, just north of Kluane National Park. This patch been broken down into 50-metre-square plots. Some are mowed. Some are provided with man-made holes and some are left alone. “So out there in this meadow we’ve got every possible combination of short grass, tall grass, burrow augmentation and just natural burrow density,” he says.

Then the long watch begins. Which squares attract and maintain the most squirrels? Which ones see the most carnivore predation? Which are most quickly abandoned?

The Arctic ground squirrel has been a feature of the Yukon landscape for the better part of a million and a half years, says Werner. “When the ice advanced, many animals pushed south. When glaciers receded they slowly came back, but Arctic ground squirrels lived in Beringia all that time.”

Yukon ground squirrels survived the Pleistocene. What’s happening now?

The answers may lie in a small patch of land near the Duke River. Hopefully, the iconic little ecosystem engineers can be saved, along with the creatures that depend upon them.

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 http://www.yukoncollege.yk.ca/research/publications/your_yukon.