Creatures vs. climate: The Virginia opossum

With snow cover on the decline across Canada, North America’s only marsupial is now making itself at home farther north
By Tim Alamenciak - Published on August 27, 2018
a Virginia opossum
The Virginia opossum is at home in urban environments, where it can readily scavenge for food. (iStock.com/randimal)

Much like human teenagers, adolescent Virginia opossums try to get as far from their parents as possible. The grumpy-looking marsupials are especially wide-ranging — and they frustrate researchers by constantly poking their noses into new territory.

“A lot of people have tried to figure out what the opossum’s home range is, and it’s a frustrating endeavour. You look at an individual, and it will completely vary,” says Lisa Walsh, an opossum researcher and PhD candidate at the University of Michigan. “Some of them move long distances in one night — the longest record for one night was 3 kilometres.”

Walsh found that snow cover has a significant effect on opossum survival. The creatures don’t like to forage when there’s lots of snow on the ground. They’re also sensitive to low temperatures — in colder climates, Walsh says, opossums often lose digits or pieces of their tail to frostbite.

“Because they don’t like to go out and forage when winter temps and snow are extreme, they can lose up to 40 per cent of body mass from start to finish in one winter season, which is a huge amount,” Walsh says. “There seems to be this point where they have to be at least 2.5 kilograms before winter sets in, so the earlier they’re born and the more they eat in the fall seems to decide whether they’ll last these harsh winters.”

With climate change causing warmer-than-average winters, though, new regions are becoming increasingly hospitable to the opossum. (Snow cover across Canada has been declining since the 1970s, according to Environment and Climate Change Canada.)

North America’s only marsupial, the Virginia opossum is a scavenger — and that makes it right at home in dense urban environments, where there are plenty of food options. (They have long existed in Toronto, but Walsh says they are spreading farther north.) It’s also among the few creatures that eat ticks, which, partly as a result of climate change, have established populations across Ontario. An opossum can consume thousands of the blood-sucking arachnids in a single day.

Walsh said the farthest north the species has been found is Grand Forks, North Dakota — which is at roughly the same latitude as Wawa. It’s still unclear how well the opossum is adapting to northern winters and whether it’s changing its habits (by, for instance, storing food for the winter, or building up more fat stores than opossums in warmer climates have). Walsh has been sampling from across the marsupial’s range to see whether opossums in colder climates differ genetically from those that live in warmer regions.

The results of that research could indicate whether cold-dwelling opossums are genetically different from their warm-climate counterparts.

It seems as if opossums will continue to expand northward. The only thing that could prevent them from doing so, Walsh says, is forage-inhibiting snow cover.

“I think especially if we continue clearing land, we’ll see them keep moving north,” Walsh says. “As long as there isn’t so much snowfall that prevents them from foraging, they’ll be successful.”

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