A Season of Snowy Owls

By Pat Leonard
From the Spring 2014 issue of Living Bird magazine.
March 15, 2014
Snowy Owl by Gerrit VynSnowy Owls spend the summer breeding season north of the Arctic Circle hunting lemmings and other prey. When the lemming population booms, the owls can produce double or triple the usual number of young, some of which may travel farther south to find food. Photo by Gerrit Vyn.
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The Snowy Owl is alluring and mysterious. We don’t know much about the bird, and often what we thought we knew has been proven wrong. We don’t understand their nomadic movements or their seeming dependence on the lemming to trigger breeding. And until recently, we didn’t even know whether their global population was increasing or decreasing. But now, based on two recent studies, the International Snowy Owl Working Group has announced that there are far fewer Snowy Owls than originally estimated—about 14,000 pairs rather than 300,00 individuals—and the numbers are declining. We need to learn more about a species the group believes should be “red listed” as threatened.

So, this past winter’s massive irruption in the Northeast and Great Lakes states left Snowy Owl researchers exhilarated, overworked, and sleep deprived as they scurried to capture, measure, and band owls that hunkered down at airports, in farm fields, along shorelines, and on utility poles. It was an opportunity to marvel at the sight of the birds and to gather data about a powerful raptor that trails ecstatic headlines in its wake whenever it appears in large numbers south of the Canadian border.

The first sightings came during November 2013. As more Snowy Owls rolled in, it became apparent that the main swath of the irruption stretched from Wisconsin east to New England, down through the Northeast, and along the Atlantic Coast. At least one bird turned up in Florida and another in Bermuda— both a long, long way from their Arctic tundra home. The birds will be returning to the Arctic in late March and April.

Norman Smith, director of Massachusetts Audubon’s Blue Hills Trail Museum, has been fascinated by Snowy Owls since he saw his first one at age 14. He has been banding Snowy Owls captured in and around Boston’s Logan International Airport for 32 years. By mid-February he’d already caught a record 103 Snowy Owls at Logan, banded 138, and placed transmitters on several.

“It’s the best year we’ve ever had at Logan for owls, especially so early in the season,” Smith confirms. “In an average winter we capture six to eight Snowy Owls. It’s absolutely incredible.”

To prevent collisions with airplanes at Logan Airport, Smith captures the owls with a bow-net trap, collects data, and releases them south of the airport so they keep moving in that direction. While the birds are in hand, Smith checks their condition, gets a rough idea of their age, and determines whether they are male or female. Smith estimates that 90 percent of the birds he captured this past winter were hatch-year birds, most of them males in good condition.

That corresponds with what bander Tom McDonald found in western New York, where he has been collecting data about Snowy Owls for the past 25 years. Although McDonald had less time to look for owls this past winter, he still managed to band 47 of them by early March. Like the Logan owls captured by Norman Smith, McDonald’s owls were in good condition, young, and about twothirds of them male. This irruption trumps any he’s previously seen, not only in total numbers but also in the number of owls seen at one time.

“We saw six owls sitting together on one set of docks in Rochester, all within 80 feet of each other,” McDonald says. “That’s something I’ve never seen before. When owls move into an area they attract more owls because they’re all looking for the same thing—good hunting over wide-open spaces and some high ground.”

Long-time Snowy Owl researchers such as Norman Smith, Tom McDonald, and others are eager to spread the word that the old theory about why the owls irrupt is wrong—the birds that come south are not starving to death and they’re not coming here because of a crash in the lemming population. The new thinking is that an abundance of lemmings prompts increased breeding, bigger clutches of eggs, and lots of Snowy Owl offspring. Those young birds have to venture farther south to find food as they disperse from their home territories at the end of the breeding season. Northern Quebec reportedly had a big lemming year and some of the owls in the recent irruption probably came from there.

The irruption brought Smith, McDonald, and other Snowy Owl researchers together in a loosely organized effort called Project SNOWstorm. Naturalist and author Scott Weidensaul is one of those who spearheaded the project to collect a mother lode of data while the snowies were in town.

“People stepped up in a way I’ve never seen before,“ says Weidensaul, “We got help from labs that do DNA blood work, from licensed banders, experts with GPS transmitters, state and federal wildlife vets and pathologists, rehabbers, and website developers, not to mention the vital observation information we got from citizen scientists using eBird.”

One arm of the SNOWstorm effort was devoted to attaching GPS transmitters to some of the birds to learn more about their movements. When a likely candidate was located, a licensed bander would capture the bird, collect a blood sample, take measurements, note its physical condition, and take a tiny snippet of feather for analysis, in addition to banding it. DNA and feather tests can confirm gender and even reveal what toxins the owl was exposed to here and in the Arctic. Then they attach a small backpack transmitter to the bird.

“These are special solar-powered GPS transmitters made by Cellular Tracking Technologies,” Weidensaul explains. “They record the bird’s location and are programmed to send a data point every 30 minutes via cellphone towers. The packs weigh less than 40 grams, which is fine for a bird as big as a Snowy Owl. It doesn’t interfere in any way with its flight, and we’re making sure to tag only healthy birds.”

The first two radio-tagged SNOWstorm owls were “Buena Vista,” which was trapped in Wisconsin, and “Assateague,” who got his moniker from the island of the same name off the coast of Maryland where he was first seen. Animations of the tracking data showed birds with very different hunting strategies. Buena Vista hung around within a one-mile radius of where he was tagged, in prairie and marsh. Assateague zigzagged all over the place along the coast, resting by day and traveling or hunting by night. “Four of the owls have spent considerable time on Great Lakes ice,”says Weidensaul. “The owl named Erie spent most of February on the frozen surface of Lake Erie, moving up to the Canadian coast, east almost to Buffalo and back again. By comparing his tracks with satellite imagery, we can see that he’s focusing on open-water gaps in the ice sheets, and presumably hunting waterbirds.” By early March, SNOWstorm volunteers had put transmitters on 16 owls in 8 states, with another 7 planned.

Snowy Owl Facts

  • In the Arctic, Snowy Owls are diurnal by necessity because daylight lasts 24 hours a day in summer. But when they move south, they become primarily nocturnal hunters like most owls.
  • Female Snowy Owls are about one-third larger than males.
  • Snowy Owls have less-well-developed sound-muffling fringes on their feathers than other owls; they use speed instead of stealth and catch prey on the wing.
  • The Snowy Owl is probably the oldest bird species recognizable in prehistoric cave art.
  • The acuteness of their hearing allows Snowy Owls to locate lemmings as the rodents tunnel through the snow.

The first two New York birds to receive solar transmitters courtesy of Project SNOWstorm were captured and released by Tom McDonald in late January, during a howling snowstorm. Braddock and Cranberry, named for Braddock Bay and Cranberry Pond, were both young males. Tracking data for both birds revealed that they never strayed from Lake Ontario, a deeper lake with less icing than the other Great Lakes.

Both birds have displayed a preference for riding on ice rafts in the lake,” McDonald reports. “Cranberry drifted several miles out from shore on one occasion. It appears both owls have been actively hunting waterfowl at night from these rafts.”

The technology has some limitations. Because the transmitter is powered by sunlight, the lack of it means no data is phoned in. But each unit can store up to 100,000 GPS locations, which will be transmitted when sunlight returns to power the transmitter. The backpacks are meant to stay on the bird and collect data even after they return to the Arctic. The Holy Grail would be to recapture one or more of these tagged birds if they come south again.

“Think of what we could learn about where they’ve been, where they stopped, and how long it took them to get there,” Weidensaul says.

Norman Smith began placing battery-powered transmitters on Snowy Owls at Logan Airport in 1999. He wanted to prove that the birds did indeed survive and make it back to the Arctic. Out of the 12 birds outfitted with transmitters that first year, three were shot before they could leave Massachusetts, but all nine of the others did make it back north. In 2011, Smith put a transmitter on a Snowy Owl that flew all the way to Nunavut and then came back to Logan the following year, having covered more than 7,000 miles.

Field researcher Denver Holt, founder of the Owl Research Institute in Montana, has been studying Snowy Owls on their breeding grounds in Barrow, Alaska, for 22 years. He began putting satellite-tracking transmitters on Alaska owls in 1999, hoping to get a better picture of their movements. It turns out these birds are doing a lot of east-to-west meandering, too—traveling from Alaska to Russia, then back to Alaska, then to Canada, all over a period of a few years.

“They move all over the place in the Arctic, covering thousands of miles,” said Holt. “During the winter, some Snowy Owls may stay up north and do this east-west movement, while others will do the north-south movement. That’s one of the reasons it’s so hard to come up with a general migration pattern for these birds.”

Lemmings are the key to the mystery. While studying the Snowy Owls in Alaska, Holt has also been studying lemming populations. “If lemming populations are high on our study site, so are the numbers of Snowy Owls and they can produce bigger clutches of eggs,” he says. “If lemming populations are low, fewer Snowy Owls show up at our site and few or none will breed.”

No one has been able to pinpoint what causes the boom-and-bust reproductive cycle of these small rodents or exactly why Snowy Owls will only breed if there are lots of lemmings. “Are the owls moving around the Arctic to track lemming populations that are abundant enough for them to stop and breed?” wonders Holt. “Satellite tracking is a great tool, but it’s just a beep on a map. We actually have to go to these places, see what the birds are doing, and assess lemming populations—we need to do some ‘ground-truthing.’ And then we need to revisit the previous year’s breeding locations to determine if there are no Snowy Owls and the lemming populations have decreased or crashed. This is the only way to say with some confidence that the owls are searching the Arctic for lemmings in order to breed. If we do not do this, then we are just speculating.”

The desire to know more about the Snowy Owl goes beyond the desire to understand the bird for its own sake. “Snowy Owls are an indicator of the health of the Arctic environment,” said Holt. “When there are lots of Snowy Owls in my study area in Alaska, everything has a better year—ducks, foxes, weasels, geese, shorebirds, and more.”

Creatures that live in the Arctic are likely to be among the first to be affected by climate change. Even a slight rise in temperature and partial thawing of the permafrost could lead to brushier vegetation, which will make it more difficult for Snowy Owls to catch lemmings.

“I have a lot of confidence in the Snowy Owls’ ability to adapt,” says Tom McDonald. “Their ability to take a variety of waterfowl and other birds will play a key role in the long-term survival of the species. But nest sites, in my opinion, are going to be in peril and the birds might need to shift their nests closer to water to take advantage of waterfowl. How fast they’ll be able to adapt compared to the speed of the changes in the tundra—that’s the big question.”

“There obviously is change going on in the Arctic,” Smith agrees. “You look at a place like Greenland where there’s been a transformation of some of the tundra from grasses to shrubs and even willow trees. That habitat is not suitable for lemmings, and if there are no lemmings, the Snowy Owls don’t breed.”

And that’s a mystery too. “Snowy Owls are such voracious predators,” Smith continues. “I’ve actually photographed them taking Canada Geese, a Great Blue Heron, and many other kinds of owls. They just pluck American Kestrels out of the air. It’s amazing—they can out-fly American Black Ducks easily. Why don’t they feast on shorebirds and produce young? For some reason they’ll only breed when the lemmings are there.”

The desire to unravel some of these mysteries is what helps Snowy Owl researchers persevere through decades of hard work. That and the magnetic quality of a species from whose powerful talons they have no wish to escape.

Denver Holt is already looking forward to heading back to Barrow, Alaska, for his 23rd year of research there. “I’m just fascinated with the Snowy Owls, and I’m a hard-core believer in long-term research,” he says. “It’s fascinating to watch them raise a family. Here’s this enormous, powerful female sitting on the nest and gently caring for her chicks; if the male isn’t providing enough food or it’s a tough lemming year, the female will just scream. These are food-begging calls: ‘bring food, bring food, bring food!’ When a male is defending, he’ll bark at you first and hoot, and then he’ll attack. I’ve got scars from my butt to the back of my head!”

“I’m still amazed by them, every single one,” says Norman Smith. “Every Snowy Owl I catch is just as exciting as the first, and every single one of them is different. They have different builds, different personalities, and different hunting styles.”

Smith also feels strongly that this is a golden opportunity to involve children in exploring and understanding nature. His son and daughter have been involved in his Snowy Owl research since they were two years old and often helped Smith look at research questions in a new light. “Now with my three-year-old granddaughter Carmella helping out, that makes three generations of owl  researchers in my family continuing to explore how global changes will affect the owls and all of us in the future,” says Smith.

“I am absolutely passionate about this,” says Tom McDonald. “The first Snowy Owl I ever held in my hands was one of the most exciting, exhilarating experiences of my life—to see that bird glaring right through me with its beautiful yellow eyes. To this day I still have that same excitement about every bird I have in my hands, and respect for a bird that is so adaptable and so rugged and so magnificently beautiful.”

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