Some winters, snowy owls appear on Martha’s Vineyard

Snoweys look cross-eyed, but not much gets past their detection, especially a tasty rodent. — File photo by Tim Johnson

For birders on the Vineyard (indeed, for birders everywhere), there’s no such thing as the off-season. Birds are always in motion, and there is always the possibility of something interesting showing up. Island birders (along with observers across the rest of the northern U.S.) are currently enjoying an influx of one of the most beautiful and enigmatic birds in the world.

Recent weeks have seen Island reports of snowy owls from East Beach (probably the most reliable Island site for this northern visitor), Norton Point, and Sylvia Beach, where West Tisbury’s Lanny McDowell recently photographed a snowy sitting next to a group of oddly complacent pigeons. The similarity of the habitat in all of these places — treeless beach and sand dunes — will give you a sense of what these birds prefer. They also turn up in farmland and grassland away from the immediate shore (Katama and Long Point are good places to look for snowies), often perched on a snag or low rise, but this is a species you’ll never find in the woods.

Snowy owls are not exactly rare in Massachusetts; at least a few are reported virtually every winter, and in some years dozens, scores, or even hundreds hit the Bay State. But this bird, as white as its name suggests, breeds far to the north on open arctic tundra and is highly adapted to cold conditions. Many years, these owls have no incentive to travel as far south as our latitude. Periodic crashes in their food supply, though, drive large numbers of snowy owls southward in search of better hunting. The majority of these birds tend to stop in the northern tier of states, retreating northward again in March and April. But snowy owls have ranged as far south as Louisiana and southern California, and have lingered at our latitude into the early summer.

These Island reports come in the context of a nationwide spate of snowy sightings, from northern California, across the northern plains, the Midwest states, and the Northeast. The broad sweep of this influx is a bit unusual, suggesting a continent-wide (but probably perfectly natural and temporary) decline in prey numbers.

These owls are impressive birds, averaging a bit larger and somewhat heavier than our familiar red-tailed hawk. While the bulk of most owls consist largely of feathers, snowies are actually solid birds, and at least when they’re in good health, their muscular bodies are wrapped in a thick layer of fat, which serves as insulation and as an energy reserve. As you’d imagine, they are formidable predators: while their preferred prey are small rodents (notably, on their arctic breeding grounds, lemmings), snowy owls can handle mammals as large as snowshoe hares or small foxes, and routinely kill and eat birds as large as ducks.

Adult males may be nearly all white. Females generally have more extensive dark barring, and young birds (which constitute a strong majority of the birds that make it this far south) are generally darker still. But regardless of sex or age, the round head and basic white coloration of a snowy owl would be hard to mistake for any other bird. However, the species is wild, wary, and hence usually seen (or overlooked) at fairly long range. The most likely source of confusion, if you’re looking for a snowy owl, isn’t a bird at all: items like empty Chlorox bottles (which wash up into salt marsh with surprising frequency) and white plastic shopping bags (which blow there and snag on bushes) are notorious for fooling even expert observers. Sometimes the wind gives a sense of motion and life to such light plastic objects, enhancing the impression of a vigilant owl.

While good news for birders, an “irruption year” like this is unequivocally bad news for the owls themselves. Many of the birds heading south are already weakened from hunger, and the demands of a long journey and having to hunt in unfamiliar settings compound the problem. A good percentage of the snowies that reach our latitude probably die during the winter (though not as many as died in the 19th and early 20th century, when thousands were shot by misguided gunners). But like many other birds that inhabit challenging environments, snowy owls have the potential to be quite prolific. A female may lay eight or more eggs, and in a year that offers abundant prey, most or all may survive to adulthood. So the mortality of a tough winter like this one can be made up for in a year of high productivity.

The snowies that arrive on the Vineyard are relatively lucky. With substantial tracts of productive, suitable habitat to hunt on, our imposing visitors should have adequate supplies of voles, rabbits, ducks, and smaller birds to catch.

The birds already seen may linger or be replaced by others, but if past years are any indication, it is likely that the species will be with us through the winter, a reminder of how our Island fits into a much larger system of wildlife migrations.

Then, suddenly, they’ll be gone, heading back north, their destination as mysterious as their arrival.