snowy owls surprise researchers

On Herschel Island off the Yukon's North Slope, snowy owls spend their summers swooping over the tundra, scooping up lemmings and other small rodents to feed their hungry chicks.

By Claire Eamer, courtesy of the Yukon Science Institute

On Herschel Island off the Yukon’s North Slope, snowy owls spend their summers swooping over the tundra, scooping up lemmings and other small rodents to feed their hungry chicks. In winter, the lemmings are out of reach, snugged down in cozy nests under the snow. So where do the snowy owls go?

Just three or four years ago, biologists thought they knew the answer. South. The snowy owls of the western Arctic, they assumed, spend their winters on the prairies, where spotting a fluffy white owl sitting on a fence post – looking like a pile of snow – is not uncommon.

And then came the International Polar Year and a circumpolar research project called Arctic Wildlife Observatories Linking Vulnerable EcoSystems, or ArcticWOLVES for short. The project, involving more than 40 researchers from nine countries, aims to understand how plants and animals fit together in an arctic ecosystem. Including snowy owls.

Frank Doyle, a specialist in raptor ecology and a member of the ArcticWOLVES team studying the Herschel Island ecosystem, talked about the project at a recent Yukon Science Institute lecture. He explained that figuring out how an ecosystem works, in detail, is a challenge.

“Physicists have got it easy,” Doyle said. “This is really complicated stuff.”

One of the complications is the snowy owl. The migration pattern that biologists were so sure they understood turns out to be a myth. The birds, or most of them, stay in the North. They might wander hundreds of kilometres over the winter, but they travel more east and west than south.

At Herschel Island, Doyle and his colleagues managed to capture four large female owls and fit them with satellite transmitters. The transmitters can send information about the owls’ locations for three or four years, Doyle said. In the late winter of 2010, they’re just reaching the end of their life expectancy, but they’ve done their job.

The four owls have covered thousands of kilometres since their transmitters were installed in 2008, and all of their journeys have been tracked and mapped. They don’t travel south, and they don’t travel together. The Herschel owls have ranged across most of the western Arctic, from western Alaska to the mainland and islands of the Northwest Territories at the eastern edge of the Beaufort Sea.

Sometimes they’ll linger in one area. One owl spent months in a single small valley in the Brooks Range, Doyle said. Because satellite tracking can’t show small movements, the researchers weren’t even sure the owl was moving at all.

“We thought the bird was dead.”

One owl flew across most of Alaska to spend time in the Kuskokwim River valley before heading back northeast to the mainland of the Northwest Territories, east of Tuktoyaktuk, all between June 2008 and January 2009. In 2010, another snowy owl spent her second winter flitting from side to side of a valley in the foothills of Denali National Park in Alaska. She was still there just a week or two ago.

What are the owls looking for? A good food supply is the obvious answer, said Doyle. When the lemmings disappear for the winter, the owls take off. They don’t necessarily spend the winter in the same place every year, but the four owls that were tracked by satellite checked out previous wintering locations. Sometimes they stayed for a while, and sometimes they moved on.

Most of the owls’ wintering locations are difficult and expensive to reach. However, with a bit of help from US Fish and Wildlife Service biologists, who visited many of the sites the owls use, Doyle and his colleagues know that the owls are hanging out where ptarmigan and, perhaps, snowshoe hares are plentiful. Although snowy owls spend their summers hunting much smaller animals, they’re well equipped to hunt something as large as a hare. Their claws are large, with strong, sharp talons, Doyle said.

“They’re really a tool best suited for killing large prey.”

In fact, elsewhere snowy owls have been seen hunting birds as big as sea ducks, herons, and even occasionally other snowy owls. One was even spotted taking a peregrine falcon, right after the falcon had killed a shore bird.

In spring, the satellite-tracked owls head back toward the arctic coast, but they don’t necessarily return to Herschel Island. Some have gone on to Banks Island or other locations near the coast. If they’re breeding – and snowy owls don’t necessarily breed every year – they need a good supply of lemmings. That appears to be more important than a specific nesting site, since snowy owls don’t waste a lot of energy on a nest.

“It’s just a scrape in the hillside,” Doyle said. “It’s not distinctive in any way.”

While lemmings are available, the owls scoop them up in large numbers. Doyle has studied the snowy owls’ summer diet by examining their pellets, the regurgitated remains of the indigestible bits of their prey. One large owl pellet, 13 centimetres long, contained the bones and hair of 10 lemmings.

When lemmings get scarce in the fall, the snowy owls set off again on their winter travels. But not south. And it’s not just the Herschel Island owls, Doyle said. ArcticWOLVES researchers have found that snowy owls from all parts of the Arctic tend to stay in the Arctic year-round. In Canada’s eastern Arctic, they head out to sea, probably hunting sea ducks at polynyas, the permanent breaks in the ice cover of the Arctic Ocean. Elsewhere, they follow different patterns, but northern snowy owls tend to stay in the north.

“Our snowy owl in the North just does what it can to survive,” Doyle said.

And, by the way, the snowy owls’ travel patterns were a surprise to biologists, but not to everyone. The Inuit knew, Doyle said, “but nobody ever asked them before.”

For more information about ArcticWOLVES and its research, go to http://www.cen.ulaval.ca/arcticwolves/index.html.

This column is co-ordinated by the Northern Research Institute at Yukon College with financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon.