More powerful than any other North American owl, faster than a scurrying lemming, able to withstand Arctic cold, the snowy owl is the Far North's toughest bird
Forty-three summers have passed, but David Parmelee vividly remembers the day on Baffin Island in the Canadian Arctic when a snowy owl almost scalped his mentor, noted ornithologist and bird painter George Miksch Sutton. Parmelee, then a graduate student, had found his first snowy owl's nest on a ridge some distance from their camp, and with excitement he carried the news to Sutton. Hurrying back to the site, the two men were ambushed from behind by the male owl, which used its formidable talons to pull hair from Sutton's head on the first swoop. With its second blow, the bird opened a deep gash.
"Oh my, the blood was flowing," says Parmelee, now curator of ornithology at the University of Nevada, Las Vegas. "Those owls never would give us any quarter when we entered their territory." Snowy owls are usually docile in the presence of humans on their winter range, but biologists never know how the birds will react on their breeding grounds. What is predictable is that the owls will attack any wild animal that poses a threat to their eggs or young. Parmelee once watched a male snowy owl rout a pair of wolves that were loping across the raptor's patch of tundra with no apparent nest-robbing intentions.
Years of Arctic field work by those two scientists--starting with Sutton's studies on Southampton Island in 1929-30--provided the foundation for most of what is known today about the owl's breeding ecology. But decades later, the bird still keeps some serious secrets: Where do snowy owls go, and how do they cope in summers when there are few lemmings, those 6-inch-long tundra rodents notorious for their dramatic population cycles--and a mainstay of the owls' diet? And what factors trigger the owls' unpredictable migrations
Only the toughest bird could rule the harsh lands between treeline and the polar sea. The snowy owl, with its 5-foot wingspan and a weight of 4 to 6 pounds, is not only North America's most powerful owl but the largest avian predator on the barrens.
It flies from lookout to lookout with stiff, jerky wingbeats that suggest an immense white moth. And if there is a prodigious supply of lemmings, a trend the birds seem able to foretell, the number of owls in any given area can be astonishing. One 1957 paper often cited in the scientific literature reported between 15,000 and 20,000 snowy owls at one time on the 25,000 square miles of Banks Island in the Beaufort Sea. The rodents' density can be as high as 160 animals per acre.
In summer months, lemmings live in shallow burrows or under lichen-splashed rocks. In winter, the rodents curl up in balls of grass and moss beneath the snow and ice, scurrying about in a maze of tunnels and emerging to feed on the buds, twigs and bark of dwarf tundra shrubs. Snowy owls, Parmelee says, "wait on a snowdrift for a lemming to poke its head outside." But melting snow, he notes, quickly floods the rodents' winter living places. "For a brief time, the tundra is crawling with wet, bedraggled lemmings."
Few birds are as sensitive to the abundance or scarcity of one kind of prey during the breeding season as the snowy owl. An owl will take the occasional eider or ptarmigan, snow bunting or Lapland longspur, even fish such as char. But by one estimate, an adult snowy owl eats three to five of the 3-ounce lemmings a day, and a pair with a brood of nine owlets--not an unusual number--would consume 1,900 to 2,600 lemmings between May and September. When the lemming population crashed on Banks Island the year after the peak reported in 1957, only 2,000 owls were counted, and few pairs tried to breed.
Conventional wisdom, in fact, says that snowy owls have a successful nesting season only once every four or five years--and that the large clutches the birds produce during lemming feasts (as many as 16 eggs per nest) and an incredible nesting success rate of close to 100 percent keep the birds' numbers strong through lemming famines. That view, however, appears to be simplistic. Lemming population dynamics are complex and, Parmelee points out, the fluctuations vary between species as well as from higher latitudes (where only varying lemmings occur) to lower latitudes (where both varying and brown lemmings are found). There is no evidence, he says, that lemming booms and busts are synchronized over vast areas of the Far North.
Moreover, snowy owls have no fidelity to particular breeding grounds. So if thousands of owls disappear from a place like Banks Island during a lemming low, Parmelee says, "they've got to be someplace else." He is convinced nomadic breeding populations move around the Arctic, nesting wherever lemmings are abundant.
Not surprisingly, lemmings play an essential role in the snowy owl mating game. The male carries a dangling rodent in his beak during an undulating courtship flight that ends in a gentle descent to a favorite perch, wings set in a glaring white "V" that can be seen a mile away. After dropping the catch on a pile of uneaten lemmings, he hoots his way through a sequence of bizarre poses until, at the end of the ritual, he grovels before an available female. Presumably, this display conveys a message that the male owl is a capable provider and that there are enough lemmings for nesting to begin.
The female owl begins her incubation duties the moment the first egg is laid. "Snowy owl eggs are as tough as they come," Parmelee says, "but they will freeze solid if left exposed to the mercy of polar winds." Egg-laying proceeds slowly--about one every two days--and the oldest owlet often wanders away from the crowded nursery long before its youngest sibling hatches.
In the case of large clutches, the female snowy owl must remain at the nest without relief for more than two months until the last chick leaves. Meantime the male, hunting around the clock in the land of the midnight sun, brings lemming after lemming to his mate, which accepts them in another elaborate ritual before feeding the nestlings. He also drops fresh prey near the hiding places of older owlets, which begin to fly and hunt lemmings when they are about seven weeks old but still depend on parents for food for another week or two. The full cycle, from the laying of the first egg on the tundra to the independence of the last owlet, consumes three and a half months, the whole Arctic summer.
A few weeks later, some of these young snowy owls will be hunting Norway rats, not lemmings, at Boston's Logan International Airport, where they are likely to encounter Norman Smith, the director of Massachusetts Audubon Society's Blue Hills Trailside Museum in nearby Milton. Every winter, Smith patrols the grasslands and salt marshes beyond Logan's busy runways, trapping and marking snowy owls that appear in significant numbers one year and are scarce the next. January 11, 1987, was a special day: Smith counted 23 snowy owls on his rounds along the airport's perimeter road. A record 49 owls showed up at the airport that season, compared with low counts of 5 last winter and during the winter of 1980, when the self-taught naturalist banded the first of more than 200 of the Arctic visitors.
Most of the snowy owls Smith sees at Logan are juveniles, identified by heavy barring on their white plumage. A few of them stick around the airport all winter. There's plenty of food--not just urban rats but also meadow voles, which are relatives of lemmings, as well as black ducks and Canada geese in the coastal ponds. He has also seen snowy owls strike down other birds of prey: short-eared owls, kestrels, a harrier. "They stoop on flying prey like a large falcon," Smith says. He adds that the birds revert to characteristic owl behavior in winter, when they do most of their hunting at night.
Typically, though, the Boston owls like to move around. A bird Smith marked with a green splash on the back of its head in early November 1991 flew north 125 miles to Bath, Maine, in time for the Christmas Bird Count; returned to Logan for a few days before winging out to Martha's Vineyard; dropped in at Ninigret National Wildlife Refuge on the Rhode Island coast; and then spent a couple of days at the Boston Harbor lighthouse before reappearing at the airport, where it stayed until May 20.
Several juvenile birds banded by Smith have returned to Logan as adults the following year, and his observations may help in some small way to sharpen the fuzzy picture of the snowy owl's winter habits. The classic view is one of a hardy resident species that is forced to leave the Arctic in huge numbers every few years when lemming populations crash across the tundra.
Synchronized irruptions do occur both in the East and West, and snowy owls have wandered as far south as central California, Texas and Florida. However, recent field studies and a review of Christmas Bird Counts show that a large part of the snowy owl population, dominated by adult birds, migrates annually to the tundralike Great Plains of Canada and the northern United States--and the birds' numbers do not fluctuate in a cyclic pattern. Parmelee adds that owls in invasions east and west of the plains come from breeding areas covering such a vast area of the continent that factors other than lemming peaks and valleys must be nudging the birds southward.
Smith's one big wish is for funding that would enable him to attach satellite transmitters to several snowy owls wintering at Logan Airport. "Then we'd know where they spend the summer, what their migration routes are and whether they choose the same destinations each year."
Curious owl watchers everywhere second the motion.
Field Editor Les Line laments that snowy owls have always been someplace else during his visits to the Alaskan Arctic.
A Bird Built for Cold
Extreme cold doesn't bother snowy owls any more than it bothers polar bears: The insulation provided by the birds' remarkably thick plumage equals that of Antarctic penguins. Snowy owls have been found nesting as far north as Cape Sheridan on Canada's Ellesmere Island, almost land's end in the North American Arctic. University of Nevada ornithologist David Parmelee notes that the owls will appear on their snow-covered breeding grounds "long before the first trickle of spring thaw."