Wildlife
Snowy owls have evolved to survive the harsh environment of the Arctic tundra, but can they survive its warming?
A gale-force wind drives freezing rain directly at me as I hunker down in a roadside ditch. When I’m not wiping water from my camera, I peer through a telephoto lens at a female snowy owl perched on the ground, just 30 metres away. Apart from a cursory glance my way when I first emerged from my car, she ignores me. I have photographed this owl more than a dozen times in recent weeks in the same farmer’s field and along the same road in southwestern Ontario. Building trust. Now she’s comfortable enough to hunt meadow voles and mice while I snap away.
I hear nothing, but a change in the owl’s stance tells me she has detected something moving beneath the snow in the ditch to my left. Feathers around a black bill help direct sound to her ears, allowing her to home in on her prey. Owls are far-sighted, so her large yellow eyes can also pick out prey at great distances and, because she can also turn her head roughly 270 degrees, her peripheral vision is sublime.
When it comes, the attack is swift. Serrated feathers along the front edge of her wings deaden the sound of flight as she darts past me, barely a metre above the snow. The unsuspecting rodent is snatched up in her deadly 3.5-centimetre-long talons. She carries her prey back into the field, then, turning to face me, swallows it whole in a series of gulps. The indigestible parts — fur, bones and cartilage — will be regurgitated in a pellet sometime tomorrow.
Over the past decade, I have been mesmerized by hundreds of similar encounters as migrating snowy owls find their way from their Arctic breeding grounds to southern Canada each winter in search of food. I estimate that I’ve spent some 2,000 hours observing these incredible birds of prey. Selfishly, I wonder how much longer my good fortune will continue.
In 2021, Bubo scandiacus was classified as “vulnerable” to extinction by the International Union for Conservation of Nature, which estimates the worldwide snowy owl population to be between 14,000 and 28,000. Though a truly accurate count is almost impossible, there is widespread agreement among researchers that their numbers are in serious decline. The next population assessment might well see their status downgraded to “endangered.”
In years when Arctic lemmings, their principal food, are abundant, breeding females lay more eggs, and more young survive. This is known as an “irruptive” year. Stiff competition for food then leads the younger, less experienced hunters to migrate farther south that winter in search of other food sources, such as voles, mice and rabbits.
Most migrants making their way to eastern Canada each winter are yearlings born the previous summer. As the young snowy owls head south, their initial encounters with humans can be deadly. Vehicular
strikes, electrocution on hydro poles and poisoning are just some of the perils they face. At only six or seven months old, they are almost completely full-grown, with a height of roughly 65 centimetres and a wingspan of more than a metre and a half. The immature owls are easily identified by their plumage, which is still heavily barred, the males less so than females. An adult male snowy owl is almost entirely white.
Today, the owls must navigate the dangers posed by another devastating foe: climate change. Jean-François Therrien has studied snowy owls for 15 years, looking at how the changing Arctic ecosystem is affecting the owls. “We are concerned,” says Therrien, a researcher at Laval University in Quebec City. “Climate change is happening in the Arctic. And even though the changes don’t appear fast, we know the Arctic is shrinking because of warmer temperatures. It is becoming more like a boreal forest.”
Therrien is a member of the International Snowy Owl Working Group, a loose affiliation of snowy owl researchers from Canada, the United States, Norway, Russia and Greenland, as well as Project SNOWstorm, a research organization committed to promoting conservation of the owls through public outreach and education. Rather than travelling north to the owls’ Arctic breeding grounds as he does most summers, Therrien spent most of last summer working from his U.S.- based office at Hawk Mountain Sanctuary (a wild bird sanctuary located along the Appalachian flyway in eastern Pennsylvania). That’s because 25 field researchers who had arrived before him at Bylot Island, a nesting spot off the northern end of Baffin Island in Nunavut, were unable to find a single snowy owl on their study site.
“I have 10 transmitters ready to deploy on fledglings to assess their dispersal and survival rate, and now they are sitting in a box in my office,” he says with a shake of his head. “It’s a bit frustrating, but that’s the nature of working with snowy owls.” Because snowy owls are so irruptive, they go where the food is, descending on one area one year and deserting it the next, in tandem with fluctuations in the lemming population (see map, below).
While most birds migrate straight back to their breeding sites, snowy owls “just prospect and zigzag and cover huge distances trying to locate those regions with an abundance of lemmings,” Therrien explains. He says it’s fascinating to watch the birds he and the other researchers are tracking, charting their patterns of movement each spring as they scout vast areas. “All of a sudden, they stop moving and breed.”
Therrien has been travelling to the Canadian Arctic — mainly to Bylot Island — since 2007 to study snowy owls, but the pandemic prevented him from visiting in 2020 and 2021. Adding to his frustration was satellite imagery that indicated 2021 was a splendid year for breeding owls on the island.
Now he wonders what to do with his GPS transmitters. In 2018 — another “off year” for lemmings at Bylot Island — he instead took some GPS transmitters to Utqiagvik, Alaska, about 560 kilometres north of the Arctic Circle. There, he collaborated with Denver Holt, the founder of Montana’s Owl Research Institute. Holt has been researching owls and lemmings for more than three decades on the tundra around Utqiagvik. Across a 160-square-kilometre survey area, Holt normally expects to find dozens of nests. In the summer of 2021, he monitored five nests, but only one produced chicks. Last summer, he found just one.
GPS units are crucial to researchers looking to better understand the snowy owls’ migratory behaviour and philopatry — their dedication to a certain migration site. Therrien describes them as “the smallest backpacks you can imagine.” The transmitter, which weighs just one per cent of the owl’s body mass, is attached over the shoulder and sits on the bird’s back. It transmits the owl’s location every few days via cell phone towers.
Among Therrien’s collaborators is biologist Karen Wiebe, who recently retired from the University of Saskatchewan. After a decade spent studying snowy owls, she remains committed to that research, mainly studying the owls that choose Saskatchewan farmland as their hunting grounds each winter. Wiebe and her team trap individual owls, assess their health, band them, then affix GPS transmitters. The transmitters have allowed Wiebe and her fellow researchers to accumulate a solid base of data, including breeding locations, migratory tracks and searching tracks.
Wiebe has also studied the body condition and mortality of snowy owls on the Saskatchewan prairies. She and colleague Alex Chang studied a total of 537 owls captured in south-central Saskatchewan over 18 winters. The study confirmed what they had predicted: adults were heavier than juveniles, and females tended to put on more fat over the winter than males. More importantly, it dispelled the myth that owls migrating to southern Canada were in poor health.
In contrast to observations in Ontario and Quebec, where most winter visitor owls are juveniles, Wiebe has found that most of the owls on the Prairies are mature, with a 50:50 split of males and females. It makes sense. Mature owls are more experienced hunters and will claim the best hunting sites nearer to the Arctic, thus avoiding the nearly 4,000-kilometre migration the yearlings endure as they head to southern Ontario and Quebec.
Like other raptors, snowy owls exhibit reverse sexual dimorphism — females are about 30 per cent larger than their male counterparts owing to the need for additional fat stores. They are also more aggressive. They may tolerate males on their turf, but only until it’s time to hunt. An hour or two before sundown, they will sometimes physically attack the males, chasing them off their hunting grounds before the rodents start to wake up and move around.
While meadow voles, mice and other rodents are the gourmet choice of snowy owls, one young male I observed last winter had a preference for rock pigeons and persistently chased them around a grain silo. And I once watched a yearling female catch a kestrel and eat it right in front of me. Others spend their winters near the Great Lakes and adapt by hunting ducks and shore birds.
Given that snowy owls have a mortality rate of 50 per cent in the first year and a life expectancy of roughly 12 years, I often wonder if the yearling I watched from that roadside survived the following summer. Will she return to southwestern Ontario in subsequent years? As climate change transforms the Arctic irrevocably, the long-term fate of snowy owls remains murky. They have evolved to thrive on the tundra, flying huge distances to follow their food sources. But as their ecosystem falters — in both the North and south — these iconic predators may be running out of time.
This story is from the November/December 2022 Issue
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