Winners and losers in the thaw

Photo by Carl Vizzone

Most years we experience a cold snap in early January and a thaw somewhere in the middle of the month. This year we got extremes of both.  For two solid weeks after Christmas, a high of minus ten felt warm, with many nights well below minus 30. Then Mother Nature flipped a switch: in the rest of January, Muskoka saw 13 days with above zero temperatures.

That kind of unseasonable temperature swing brings a mixed bag of opportunities. The freeze after the thaw ended turned lakes into skating rinks, giving skaters a chance to travel for miles on clear ice. Skiers and snowmobilers, on the other hand, saw a few weeks of miserable conditions before the snow returned at the beginning of February.

Wild creatures see a similar mix of winners and losers in this kind of weather. For mice and other small rodents, for example, an extended thaw is really bad news. That’s because they get through the winter by burrowing tunnels under the snow, where they live in relative warmth and safety. While the thaw wasn’t enough to melt all the snow in the woods, it certainly reduced the snow cover considerably, making it much easier for predators like foxes and coyotes to find a mousy meal.

Coyotes actually get a double bonus from a thaw followed by a freeze, but this one comes via much larger prey animals: deer.

White-tail deer are near the northern edge of their range in Muskoka – the deep snow and harsh winters of Northern Ontario are better-suited to moose. But as long as the snow isn’t too deep, deer’s long legs let them move around with a bit more ease than coyotes and wolves can.

But a protracted thaw followed by a freeze makes the crust of the snow hard. Anyone who has ever tried to walk through crusty snow knows how difficult it can be – your feet break through, but you can’t just shuffle forward the way you can in deep, fluffy snow. But lightweight coyotes, with their broad paws to disperse their weight, can run on top of the crust, giving them a huge speed advantage over the deer. Count this as another win for the predators.

It isn’t just the freeze-up that causes problems for wildlife, though. The thaw itself can bring challenges for northern species that are adapted to long, cold winters.

The grey jay is, without a doubt, one of winter’s true survivors. The bird doesn’t migrate, but thrives in northern winters, even building its nest and laying eggs in February or March, which is one of the reasons the Canadian Geographic Society picked it as Canada’s National Bird.

One of its survival tricks is that it stores food in the fall. It produces sticky spit from oversized salivary glands and stashes thousands of meals of seeds in bark cavities and under branches throughout its territory. Studies show that the birds seem to remember where each of these food caches is stored, an incredible feat of memory. But for grey jays, a thaw in January is like a power outage that turns off the freezer: its fine for a short while, but eventually the food starts to spoil. This may, in fact, be one of the reasons grey jays aren’t found in southern Ontario – the winters there are just too mild.

Plants have also evolved to adapt to a wintry season. And, like the grey jays, they can suffer when things get off-kilter. One of the worst things that a plant can do when it warms up is to think that spring is here, and start shedding its winter coat. If buds start to swell with moisture, they will freeze when the icy weather returns. The same can happen if sap begins to return to tree branches too soon: a minus 30 night will turn that water to ice, which will expand and crack the wood, exposing the tree to disease and further frost damage that can shorten its life by decades.

Fortunately, most plants also rely on changes in light angle and duration as a clue that spring has arrived. Since this thaw came in January, it’s likely that few trees were fooled.

Remember, too, that every species in the wild is part of multiple complex networks, and a change to one creature affects many others. If coyote numbers grow because they get a rich winter feeding, how does that affect rabbits? If mice population numbers drop, does that harm plants that rely on mice for feed dispersal, or owls that feed on mice?

It’s a complex web of life out there in the woods, and any extreme change has widespread impacts.






Posted in Connecting with Nature.