Wild Encounters - Wings Over Pennsylvania

Wings Over Pennsylvania

12-01-2005 // Cheryl Lyn Dybas

Each winter, short-eared owls flock to a handful of rural sites across the country, with birders following close behind

THE GLOAMING, it’s called, this twilight between day and night. In myth, the gloaming is the place between the known and the unknown, the ordinary and the extraordinary. It’s also the time when rarely seen creatures come out from the shadows.

In the frostbitten air of a February sunset over Adams County, Pennsylvania, the gloaming indeed has opened a portal to another world. To the north, south, east and west of an old farmhouse surrounded by snow, dozens of short-eared owls emerge from roosts in nearby hay bales, woodpiles and trees.

Like bats that flutter from caves at sundown, more than 45 owls suddenly take to the skies over William and Christine Arentz’s farm. While most owls hunt by night, short ears listen for their prey—small mammals like meadow voles and mice—at dusk and dawn. Crepuscular hunting, it’s called by biologists.

The Arentz farm is one of just a handful of places in the United States where short-eared owls gather in such large numbers, thanks in part to its abundance of voles—hundreds to thousands per acre, estimates one biologist. The birds arrive "like clockwork on January 1st," says Christine Arentz. Not surprisingly, birders from miles around also flock to the farm, where owls festoon bare-branched trees like Christmas ornaments.

"Usually you’d be lucky to see one or two short-eared owls in an entire winter," says Maryland-based raptor biologist Mark Causey, who says he’s come to Pennsylvania simply "to enjoy the spectacle of all these owls." It is a "breathtaking, once-in-a-lifetime experience," agrees Causey’s colleague Ken Smith.

A widely distributed species, the short-eared owl is found on every continent except Australia and Antarctica as well as on islands including Iceland, the Greater Antilles, the Galápagos and Hawaii. Denizens of tundra, meadow, salt marsh and other grasslands, short ears are also known as bog owls, swamp owls and farm owls.

But in many places the birds may not be called farm owls much longer. As more and more farmers roll up their hay bales for the last time and turn to other ways of making a living, a succession of shrubs and trees takes over their farmlands. The agricultural grasslands turn into forests.

"Loss of grassland is a major factor in the decline of short-eared owls," says Causey, a licensed raptor bander for the U.S. Geological Survey (USGS). In a study of 12 New England and Mid-Atlantic states in the mid-1980s, for example, scientists found 50 pairs of breeding owls, but today the number is thought to be in the single digits. In Massachusetts alone, researchers identified 25 breeding pairs in 1985; today there are none in the state.

Across its North American range, short-eared owl numbers declined by more than 3 percent a year between 1966 and 2001 (and by more than 11 percent a year in Canada), according to the USGS North American Breeding Bird Survey. "The worst thing for the owls is when farms are sold for housing developments," says Joseph Sheldon, an ornithologist at Messiah College in Grantham, Pennsylvania.

Pennsylvania is one of six states where the owl is listed as an endangered species, and it is considered threatened in two others. Although the bird is not included on the federal list of endangered and threatened species, biologists like Sheldon and Causey believe it should be. The species does appear on the National Audubon Society’s Watch List.

Where the owls do occur, they are more easily observed than their woodland-dwelling cousins—especially in winter at places like the Arentz farm. The birds tend to return to the same winter haunts year after year. "Where there are wide fields with good vole hunting and little or no snow cover, look for wintering short-eared owls," says owl biologist Denver Holt, director of the Owl Research Institute in Charlo, Montana.

During summer, short-eared owls nest on the ground in knee-high grasses across the northern part of North America, especially in prairie regions. According to Liam McGranaghan, a raptor biologist who teaches environmental science at Loudoun Valley High School in Purcellville, Virginia, there is an optimal grass length for attracting voles—and short-eared owls: not too tall, not too short. "Habitat is best managed for owls by periodic mowing or burning of high grasses," McGranaghan says.

Although the species’ breeding range is currently contracting, some biologists speculate that, by promoting the growth of grasses, global warming may ultimately benefit nesting owls. "Increased water from higher amounts of rainfall and snowfall in certain parts of the United States is fueling plant growth in spring," says Holt. "Where there’s more plant growth in the form of grasses, there are more voles—and more owls."

Back on the Arentz farm, cold has driven the birders back into their warm vehicles. Outside the cars’ windows, owls fill the sky on all sides. "The flight of the short-eared owl is one of the most graceful of any owl, or for that matter, of any bird," says Doug Gross, an endangered bird specialist for the Pennsylvania Game Commission. "It’s like that of a butterfly. Short-eared owls come out at sunset not only for food, but to ‘sky-dance.’"

On this February evening, the sun sets early. The gloaming, that magic twilight time of short-eared owls, soon turns to night. But somewhere out in the grasses, owls are waiting on silent wings for the next gloaming—the one that happens at dawn.

Virginia writer Cheryl Lyn Dybas went owl watching on the Arentz farm last winter.


The Long and Short of It
The name short-eared owl implies that the species has shorter ears than other owls. In fact, owls do not have external ears—short, long or otherwise. The features referred to as ears are tufts of feathers on the tops of the birds’ heads that have nothing to do with hearing. Short ears’ tufts are simply shorter than those of other owls.


A Tale of Two Raptors
The short-eared owl rules the grassland roost by dusk and dawn, but at high noon, its alter ego—or ecological equivalent, in the language of biology—is king of the fields: The northern harrier, formerly known as the marsh hawk, is a diurnal raptor that hunts for voles and other small rodents in broad daylight.

"Short-eared owls and northern harriers share the same territories, and they even look alike," says raptor biologist Denver Holt. "Both have large facial disks [feathers around their eyes shaped like inverted satellite dishes], the better to funnel sound from rustling mice to their ears."

But all is not quiet on the farmland front. By late afternoon, skirmishes may erupt between late-hunting northern harriers and early-hunting short-eared owls. Most of these fights are over food.

Biologist and northern harrier expert Frances Hammerstrom witnessed 25 such encounters in Wisconsin grasslands. "A harrier attacked a short-ear 12 times, a short-ear attacked a harrier seven times, and in five encounters, I couldn’t tell who picked on whom," she wrote in her book Harrier, Hawk of the Marshes: The Hawk That Is Ruled by a Mouse

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