The Thing with Feathers (10 page)

But the effort paid off. When I finally set up my spotting scope and peered through it, I gasped. There, filling the view, with the yellow eyes of Arctic summer and a white body of northern winter, was an immaculate snowy owl. It stared with fierce intensity and a bit of curiosity. We sized each other up for a few minutes, the owl occupying its favorite stump and my boots slowly sinking up to their brims in mud, while I snapped a couple of photos. The owl was nearly entirely white, indicating that it was probably an adult male. When I zoomed in to see if my images were sharp, I noticed some bloodstains on the bird’s white chest.

“You left a bit of lunch on your chin,” I remarked. The owl closed its eyes and sank into a snooze.

I wondered what it had been eating. We were a long way from the nearest lemming—a snowy owl’s usual snack—and I doubted any mice or voles were hiding in the muck that surrounded us. Could it catch one of those dunlins zipping around in a confusing swirl, or did it waft out over the nearby lake under cover of darkness to snatch ducks off the water? The owl wasn’t telling, and, besides the bloodstains, didn’t offer any evidence. It rested, sphinxlike, unmoving except for a couple of loose feathers that ruffled in the breeze.

I retraced my steps to my car, each one repooling into dirty
sludge, and contemplated this snowy owl’s welfare. The bird didn’t seem to be starving, exactly. I hoped it would stick around for other birders to enjoy.

But it was gone the next day. Other birders made the exhausting trek only to find the owl had disappeared. Some snowy owls, like the one in Albany, remained for weeks or even months, staking out winter territories in farm fields, suburbs, and rural areas across the northern United States. Those were the ones that appeared in newspapers and on TV. The Fern Ridge owl was just ghosting through.

—

SNOWY OWL IRRUPTIONS
have been happening as long as anyone can remember. The bird’s distinctive white body, yellow eyes, and round frame appear in prehistoric European cave paintings alongside other animals, probably the oldest human art depicting an identifiable bird.

The species was classified by Linnaeus himself, the father of modern scientific names, in 1758. Recent DNA research has indicated that snowy owls are closely related to the great horned owls of the Americas, the several eagle owl species of the Old World, and other members of the genus
Bubo
; though snowies appear to have a rounded head, they have tiny ear tufts, which are usually hidden.

They are the heaviest of North America’s owls. This was put on dramatic display about a month after I trekked out to Fern Ridge, when a photographer captured an encounter between a peregrine falcon and a visiting snowy owl in one of Chicago’s city parks. The owl, sitting on the ground, suddenly found itself being repeatedly dive-bombed by the falcon, which lived in a nearby neighborhood. The falcon probably just wanted to drive out a perceived competitor, but it’s not inconceivable that
a peregrine might eat a large, juicy owl if given the chance; I once watched a hungry peregrine falcon annihilate a smaller burrowing owl in California, and peregrines have been documented eating short-eared owls—though great horned owls, in turn, have killed adult peregrines. For its part, the defensive snowy owl became quite agitated, puffed out its feathers, and anticipated each strafing with a little hop into the air and a backward somersault, throwing up its talons for protection as the falcon veered off. After five minutes of sparring, with both birds shrieking and hissing at full volume, the peregrine gave up. The photographer called it a draw.

In a historical context, the 2011–2012 irruption event didn’t break many overall records. Washington had closer to 100 sightings than the 1,000 of 1916, and that’s with magnitudes more human observers than existed a hundred years ago. Sure, the individual snowy owls in Hawaii and Texas got a lot of attention, but even these sightings weren’t all that surprising, because snowies are nomadic birds, prone to wandering.

Some suggested that the Hawaii bird had hopped a ship to get there, but it is more likely to have flown 2,000 miles over the Pacific Ocean under its own power. Not many ships go directly between the Arctic and Hawaii, and snowy owls have been known to wander far from land. In 2012, for instance, one also appeared on Shemya Island, halfway between mainland Alaska and Japan. Over the years, they have been recorded in every U.S. state except Arizona and New Mexico, often along shorelines.

The cool thing about the 2012 irruption was that it was so well documented. Thanks to eBird, a website where birders can log their sightings on one comprehensive database, people anywhere can look at the snowy owl invasion on their own computer screen. For the first time, with just a few clicks, it’s
possible to view most snowy owl records on a map and sort them by date. This sort of control enables finer analysis from data collected all across the country by birders and garners more interesting results.

If we look at the map, it’s clear that most of the snowy owls that came south in 2012 were concentrated in the middle of the United States, with especially impressive numbers in the Great Plains. Though the Pacific Northwest and the Northeast had above-average numbers, you don’t have to go back very far to find years with more owls in those states. In the Midwest, by contrast, snowy owls were
everywhere
. The 2012 irruption in that area may have been the biggest anyone’s ever seen. Thanks to eBird, we know that the invasion varied regionally. But that still doesn’t explain how it happened.

—

SNOWY OWLS AREN’T THE ONLY BIRDS
to make periodic winter irruptions. Type the words
bird irruption
into Google, and you’ll get blizzarded with reports of redpolls, grosbeaks, crossbills, nuthatches, chickadees, and waxwings, among others.

All of these birds have something in common: They live in the far north or high mountains. And every few winters, large numbers of them show up in lower, more southern areas, outside their normal range.

These winter irruptions are generally thought to arise from food shortages. Redpolls, for instance, forage on catkins; when the catkin crop fails, they hightail it south in search of something to eat. Nuthatches and crossbills depend on conifer cones, and pine grosbeaks and waxwings follow fruit. In some years, when catkins, cones, and fruit fail in the same season, many species of northern finches and other birds that depend on those food sources simultaneously invade southern areas they
don’t normally inhabit. When that happens, birders call it a superflight.

Irrupting birds generally have something else in common: They are food specialists. Unlike birds farther south, northern birds live in an area with few meal options—so they specialize. Redpolls are fine eating birch catkins as long as catkins are available, and catkins are usually abundant. When birches have a bad year, though, redpolls are forced to move elsewhere. Specialists like this are typically more nomadic than omnivorous birds because they have to keep up with a fickle food supply. This is also true of some tropical birds that specialize in particular fruits in the rainforest; like northern finches, they are known to wander widely in years when the fruit crop plummets.

Several northern raptors show similar periodic influxes, including rough-legged hawks, northern goshawks, great gray owls, boreal owls, and, of course, snowy owls, but their irruptions are less well understood than the movements of finches and other seed-eating birds. Perhaps the same effect carries upward so that plant-eating mammals, the main diet of Arctic raptors, impose boom-and-bust cycles on predators, or maybe other factors are at work. Things are more complex at the top of the food chain.

—

AS FOR SNOWY OWLS,
the more we learn about them, the more we know we don’t know.

In 1945, ornithologist V. E. Shelford published a short paper suggesting that snowy owls fly south in years following population crashes of their main Arctic food source, the collared lemming. Sometimes lemmings breed so fast that their population skyrockets, and then they disperse in search of more
sparsely occupied territory. This phenomenon has led to the false but widespread notion that lemmings commit mass suicide by jumping blindly over cliffs, but it also means that their populations are somewhat cyclic. Shelford gathered data on lemming and snowy owl numbers, plotted them on a graph together, and believed he detected a pattern.

It seemed logical. After lemming populations crashed, snowy owls would have less to eat and might have to head south in search of food. Shelford’s paper, which had cobbled together data from several different sources, didn’t spend much space elaborating on specifics. The idea was easy for anyone to understand, quickly accepted, and used as a textbook example of population dynamics for decades. Many sources still suggest that snowy owl irruptions are caused by lemming shortages, which, according to one study, occur, on average, once every 3.9 years.

The trouble is that there’s little hard evidence to support Shelford’s theory. It’s difficult to prove that invasions follow any kind of cycle; different people look at graphs of snowy owl occurrences in the continental United States and see different things. Because humans love patterns, it’s hard not to try to find regularly spaced spikes. People who argue for a snowy owl cycle generally say that irruptions occur every three to five years—but sometimes six; that invasions are sometimes, but not always, followed the next year by a smaller “echo”; that sometimes cycles are skipped altogether; and that really big invasions usually occur every fifteen years—but sometimes ten, and sometimes twenty, and occasionally back-to-back. Looking at a chart of snowy owl sightings over the past couple of decades, my eye gets the impression of regular intervals, but separating the waves from the chop is tough. One serious statistical analysis was unable to quantify any kind of pattern: Peak
snowy owl years, at least at the scale studied, could not be predicted at all.

Also, lemming numbers do not seem to follow similar trends across wide swaths of tundra. Populations in one region may experience a peak while, a hundred miles away, their neighbors are crashing. Even Shelford’s original paper pointed out that some of his lemming data showed different trends in different areas. Recent research has indicated that lemming populations are probably more of a patchwork than a unified, continent-wide force.

Shelford seemed to assume that snowy owls normally stay in one home area, but snowies move around a lot. They are highly nomadic—probably looking for a ready food supply—and many shift south even in non-invasion winters. Areas in the northern Great Plains and New England host snowy owls every single year. This makes it difficult to define what, exactly, constitutes an irruption. How many is abnormal? Concentrations of owls shift within their wintering range from year to year. Some winters there are more snowy owls in the Northeast; sometimes they’re more heavily concentrated in the Northwest. In 2012, as eBird showed us, they hit the Midwest hard.

Owl numbers do appear to be at least partly correlated with lemming numbers. After all, a healthy adult owl needs about five lemmings a day just to stay alive (which makes you wonder: Does a snowy owl wake up in the morning and think, “Yes! A lemming for breakfast! And brunch! And lunch! And two for dinner!”). If irruptions are caused by fluctuations in lemming populations, though, they may be more regional than Shelford believed. And it might not be quite for the reason he described—that lemming crashes cause snowies to move south.

The 2012 snowy owl invasion occurred after a season when
lemming populations were at all-time highs in many parts of the Arctic. That summer, owls had fared exceptionally well, rearing up to seven or eight chicks in an average nest. Normally, it’s closer to two. Suddenly all those young owls found themselves jostling for space. Territory became a limiting factor, so some of them headed south. Rather than too
few
lemmings, it seems, there were too
many
owls.

If that’s true, then the implications are slightly different for the owls seen in the Lower 48. They’re not all starving, just looking for space.

Despite widespread assumptions about starving snowy owls, many or most of them seem to be in good health. In 2012, out of thousands of snowy observations in the United States, I could find only a handful of references to birds dropping dead from starvation. Sadly, human-related injuries are much more common; one ornithologist in Kansas examined five dead snowy owls, of which three were hit by cars, one collided with a train, and one was electrocuted on a utility line. Nearby, one was shot by a poacher, and another hit a power line and broke its wing on the concrete below. Five owls in Nebraska were found with broken wings after collisions with vehicles, and two more were electrocuted there. One in Ontario had its leg wedged in a telephone pole insulator and was photographed dangling from the top of the post like a white plastic grocery bag. Of five snowy owls that were found dead in Massachusetts, all of them were trauma victims. In their usual Arctic home, snowy owls don’t have to worry about such things.

A comprehensive study in Alberta found the most common causes of snowy owl mortality to be automobiles, electrocution, gunshot wounds, and collisions with unknown objects, in that order. Only 14 percent of known deaths were attributed to starvation, and most of the owls there make it through the
winter without dying. More than half of all examined specimens in Alberta (most of which met traumatic ends) had healthy fat deposits, indicating that they were not only eating well but also had stored extra reserves of energy.

What exactly do they eat, then? Wintering snowy owls, with no access to lemmings, have a surprisingly varied palate. In the Aleutian Islands, one study documented snowy owls surviving on ancient murrelets, a type of small seabird. In the Shetland Islands, the owls eat mostly rabbits. Alberta birds focus on mice and voles. Pellets examined in Oregon show mostly black rat remains. One study of pellets from snowy owls wintering on rocky islands in British Columbia found that the owls were surviving entirely on birds, with more than twenty prey species identified; most were ducks and grebes, but there were also significant numbers of gulls, a few shorebirds, and even a short-eared owl. A particularly aggressive snowy owl was once observed carrying off a full-grown feral cat at John F. Kennedy International Airport in New York. In 2010, a snowy owl in Manitoba made off with a mini–Yorkshire terrier while the dog’s owner still held the other end of its leash; fortunately, the quick-thinking owner yanked his disappearing terrier back from the owl’s talons, and, though the dog had gone into convulsions from shock, it was unharmed. Snowy owls have extraordinary sight and hearing, are fierce hunters, and will seemingly dine on whatever is easy to catch. Females tend to take bigger prey than males.