An abnormal season is tough on animals, in lots of ways
SCIENCE by Gregory Beatty
Winter can be hell in Saskatchewan. But imagine trying to survive six months of snow and cold without a furnace to heat your home, or a grocery store to buy food at, or electric light to ward off the dark, or the possibility of a winter getaway to stay sane.
Pretty frightening, right? Yet for wildlife that’s the norm here.
“Some animals, like birds, can migrate,” says Ray Poulin, the Royal Saskatchewan Museum’s manager of research and collections. “But for a lot of mammals that’s impossible. You’re not going to have squirrels migrating to Florida.”
Monarch butterflies also migrate, as do caribou and pronghorn, but most animals stay in their home territory. And outside of a few species that remain active year-round, hibernation is a big part of their survival strategy.
Generally, hibernation involves animals storing up food reserves in the summer and fall, then finding secure shelter and dropping their metabolism to a level low enough to survive until next spring.
Declining daylight is usually the trigger for hibernation, as it’s a more reliable indicator than daily weather that winter is approaching — especially in a variable climate like ours. Even insects slow down as the days gets darker.
“When the ratio of daylight to no-daylight reaches a critical point it triggers physiological changes in their bodies, including the production of anti-freeze compounds,” says Cory Sheffield, the RSM’s curator of invertebrate zoology.
Insects aren’t the only animals that rely on anti-freeze to survive months-long exposure to sub-zero temperatures — which in non-cold tolerant mammals would cause death from water freezing in our cells and rupturing them.
“A wood frog’s heart stops beating and it stops breathing,” says Poulin. “It’s essentially a living-dead organism. It doesn’t freeze solid. It looks like it does, but it has some anti-freeze that protects its vital organs. Then when spring comes it has an interesting way of thawing and coming back to life.”
Even with anti-freeze compounds, insects still need shelter.
“Most either spend the winter in the ground or under leaf litter,” Sheffield says. “If there’s a blanket of snow, although it seems like it would be cold, it actually provides a buffer that keeps conditions somewhat warmer and more stable then if you’re exposed to the ambient air temperature.
“The work I’ve done with bees and overwintering, I’ve attached a small thermometer to their bodies, then put them in an environment where the temperature was dropped at a constant rate,” he says. “Most can go down well below minus 20 C before they actually freeze.”
For all animals, whether they’re cold tolerant or, like mammals, must live off stored energy reserves to keep their body temperature above freezing, there is little margin for error.
“When you’re living on a precarious edge, every little thing matters,” says Poulin. “When winter sets in, when it ends, how cold it is, how much snow there is.”
Variability is another concern. This year, since early September, we’ve had wild swings from freakishly warm to cruelly cold and back again. And that can mess animals up, says Poulin.
“When we had that warm December there were stories about bats in Regina,” Poulin says. “That’s deadly for them. There’s no food or water out there. And they’ve just burned a lot of energy to come back to life.”
Because of a dip in the jet stream, Alberta’s basked in Pacific coastal conditions this winter. Ski resorts have closed for lack of snow, and unusual insect activity with bees and wasps has been reported, says Sheffield.
“A good winter for most insects has good snow cover for most of the cold periods. In years where you have very little snow, or it melts and then there’s no snow cover, along with associated flooding, those are years that can be particularly hard.”
Insects that emerge too early run the risk of dying from exposure should the weather turn cold again. And there’s no food for them, because their usual nectar and pollen sources are dormant.
And then there’s global warming. Most climate change models predict increasing volatility in future decades.
That will put additional survival pressure on animal populations, says Poulin.
“The thing that can really affect animals is timing. If the cold spell starts in October, and they’re adapted for it to start in November, there’s a couple of extra weeks you’ve got to be underground, and you need the energy reserves for that.”
Longer than normal winters are equally dangerous, Poulin adds.
“Two years ago we had that huge snow pack, where the snow didn’t melt until May. I was watching for the ground squirrels. This year, they’re probably out already, especially in western Saskatchewan. So that other year, they had two extra months of deep snow cover. How do you survive an extra two months with that energy store?”
If spring is late, that can affect the breeding cycle too.
“Think of a sparrow,” says Poulin. “It’s got to get here, set up a territory, make a nest, sing and dance to attract a mate, then it’s going to lay eggs, and they’ll be incubated for a couple of weeks, or maybe a month with a bird of prey, then if they hatch it’s going to take several more weeks to feed those young so they’re able to leave the nest.
“If something happens that pushes that back a month, instead of mid-summer, it’s end of summer when they’re starting to get ready for migration, so that pushes the envelope a little more,” he says.
Add in existing survival pressure from habitat destruction through relentless human intrusion into wilderness areas, and it’s another headache animals don’t need.
“If we have a bad year, individuals might be in trouble,” says Poulin. “As for the population, it depends on how bad it is. If none can tolerate the extreme then it’s going to go. If half can and half can’t, you get a population pinch. And those that survive are probably a bit better adapted to the condition they just faced.”