At twilight in winter, short-eared owls appear over grasslands across the U.S. (Photograph: USFWS)
They emerge at twilight, the magical time when rarely seen creatures come out of the shadows.
In the balmy air of an unseasonably warm February dusk, twilight indeed has opened a portal to another world. Like bats that flutter from caves at sundown, short-eared owls take to the skies over Stonebridge Farm near Front Royal, Virginia.
While most owls hunt by night, short-ears listen for their prey – small mammals like meadow voles – at dusk and dawn. Crepuscular hunting, biologists call it.
Stonebridge Farm, betwixt Virginia’s Clarke and Warren Counties, is one of a smattering of places in the U.S. where wintering short-eared owls gather in large numbers, thanks to an abundance of meadow voles—perhaps hundreds to thousands per acre, biologists have estimated. Stonebridge Farm is surrounded by fields that stretch for miles: prime habitat for voles, and owls.
In autumn, the birds fly south from North America’s northern reaches, arriving in more southerly grasslands around the time of the winter solstice. They stay through the season, then return north by the spring equinox, says environmental scientist David Carr of the University of Virginia. Carr is also the director of Blandy Experimental Farm, the State Arboretum of Virginia. As the owl flies, Blandy is less than five miles from Stonebridge Farm.
In some places around the country, short-eared owls are so numerous they festoon bare-branched trees like holiday ornaments. “Usually you’d be lucky to see one or two of these owls in an entire winter,” says Carr. “This season, we have seven or eight at this spot in Virginia. Not surprisingly, birders from near and far have flocked to the site.”
The name short-eared owl implies that the species has shorter ears than other owls. In fact, owls don’t have external ears—short, long or otherwise. Their “ears” are tufts of feathers on the tops of the birds’ heads that have nothing to do with hearing. Short-ears’ tufts are just shorter than those of other owls.
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.
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 ultimately turn into forests.
“The loss of grasses is a major factor in the decline of short-eared owls,” says Carr. “The worst thing for the owls is when farms are sold for housing developments.”
Grassland owl on the wane
According to a report by the International Union for Conservation of Nature (IUCN), short-eared owls are rated a species of “Least Concern.” The document notes, however, that numbers of the owls have significantly declined in North America over the last 40 years: a 71.2 percent decrease. But “the decline is not believed to be sufficiently rapid to approach the threshold for Vulnerable,” the report states.
Other findings suggest more dire circumstances. “Short-eared owls are experiencing substantial, widespread and ongoing declines in North America,” write Travis Booms of the Alaska Department of Fish and Game and colleagues in a paper published in The Journal of Wildlife Management. “Short-eared owl conservation concerns have gone almost unnoticed, however. No large-scale or coordinated research and management programs are in place that attempt to understand, slow, stop or reverse this decline.”
Throughout North America, we need to better protect short-eared owls and other grassland species, the scientists believe.
In Pennsylvania, for example, the short-eared owl is a state-level endangered species, mostly a result of habitat loss, says Doug Gross, an endangered species biologist at the Pennsylvania Game Commission. Pennsylvania once had extensive farm fields; many have become townhouse complexes.
Across the country, some sites that support wintering and nesting short-eared owls have been designated as Important Bird Areas (IBAs), places identified as globally important for the conservation of bird populations. In the U.S., IBAs are administered by the National Audubon Society.
Where the owls do occur, they’re more easily observed than their woodland-dwelling kin. The birds often return to the same winter haunts year after year. “If there are wide fields with good prey and snow that’s not too deep, look for short-eared owls,” says Carr.
Researchers think there’s an optimal grass length for attracting voles—and short-eared owls: not too tall, not too short. During summer, short-eared owls nest on the ground in knee-high grasses across the northern part of North America, especially in prairie regions.
Owl by night, hawk by day
The short-eared owl rules the grasslands at dusk and dawn, but at high noon, its alter ego, or ecological equivalent, is king or queen of the fields. The northern harrier, formerly known as the marsh hawk, hunts for voles and other small rodents in daylight.
Both short-eared owls and northern harriers have large facial disks – feathers around their eyes shaped like inverted satellite dishes – the better to funnel sound from rustling voles to their ears.
“Short-eared owls take the ‘second shift’ of rodent hunting when harriers go to their night roosts,” says Gross. “The exchange between harriers and short-eared owls is a graceful aerial ballet of diving and chasing not to be missed.”
But life is not always quiet on the farmland front. By late afternoon, skirmishes may erupt between late-hunting northern harriers and early-hunting short-eared owls. Most of the fights are over the next meal.
The late biologist and northern harrier expert Frances Hammerstrom witnessed more than 20 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 Harrier, Hawk of the Marshes: The Hawk That Is Ruled by a Mouse.
On this late afternoon at Stonebridge Farm, northern harriers join short-eared owls in patrolling the fields. Today, however, there’s hawk-owl détente.
Comes the night
Nightfall eventually drives harriers to ground and birders back into their vehicles. Outside the cars’ windows, the last owls visible in the waning light course from field to field.
“The flight of the short-eared owl is one of the most graceful of any owl, or for that matter, of any bird,” says Gross. “It’s like that of a moth or a butterfly. Short-eared owls come out at sunset not only for food, but to ‘sky-dance.’”
In February, the spectacle ends early. Twilight, that time of short-eared owls, soon turns to night. But somewhere in the grasses, owls wait on silent wings for the next twilight—the one that happens at dawn.