Wild Side : Eastern screech-owls on Martha's Vineyard
Photo by Dr. Thomas G. Barnes/US Fish and Wildlife Services
Wherever you are on the Vineyard, odds are good there's an owl closer than you think. Winter is the easiest time to find these secretive birds. Even so, their habits make them hard to detect; most active birders hear owls infrequently and see them rarely, while most non-birders are wholly oblivious to their presence.
I'm setting aside two diurnal owls that visit the Island occasionally in winter (the short-eared owl and the snowy owl). And I'm ignoring three nocturnal species that are uncommon here as visitors or, sometimes, breeders: Great horned, northern saw-whet, and long-eared owls. The vast majority of owls on the Vineyard, and the species that is by far the easiest to find, is the eastern screech-owl, a hardy and remarkably adaptable bird.
"Screechers," as birders sometimes call them, are surely the most numerous bird of prey on the Island. No comprehensive census has ever been conducted, but on a good night a single observer can find ten or a dozen individuals, and the annual Christmas Bird Count (which will be on January 2 this season) sometimes turns up twice that number. Given the amount of suitable habitat that goes unsampled, there are surely hundreds of screech-owls on the Vineyard. They occur in a wide range of habitats, but a mature woodland with easy access to an overgrown field is probably their ideal setup.
Screech-owls depend on the availability of cavities in which to lay their eggs: an old hole made by flickers, our largest woodpecker, will do, as will a hollow tree trunk or limb. Screechers will use nest boxes erected by humans, too, if the entry hole is large enough (these owls are roughly the size of a jay, though plumper and shorter-tailed). And these birds are not at all fussy about specifics like what habitat a cavity is in, or how high it is off the ground. Laying their eggs in such sheltered sites, screech-owls start the breeding season early, courting during the winter and laying their eggs in early spring.
As a practical matter, their reliance on cavities means that screech-owls nest mainly in old oaks on the Vineyard, or in mature shade trees in settled areas. They're quite tolerant of human presence, since their schedules barely overlap with ours. For years, a pair nested in a hollow oak next to the intersection of Dukes County Avenue and Vineyard Avenue in Oak Bluffs (a storm has knocked most of the tree down, but thousands of Islanders passed within yards of the nest, never knowing it was there). And I sometimes hear screech-owls calling in the residential parts of Vineyard Haven, again within biscuit-toss of houses and busy roads.
It's their calls that are the key to finding these birds. Screech-owls have two typical calls. One, a quavering wail, has a unique hollow sound quality as it rises slightly in pitch, then slides down a chromatic scale. The other is a sustained, trilling whistle, on a single pitch or descending slightly. Either call is easily imitated and, at any season, even a bad imitation (like mine) is often enough to prompt a response from a real bird — sometimes during the day. An imitation or, better yet, playback of a recorded call will often prompt an owl to fly in to investigate. Quite fearless (or maybe they merely feel invincible in the dark), such curious owls can be readily viewed by flashlight.
A state of bitter enmity exists between screech-owls and many of the small birds (chickadees, nuthatches, titmice, and wrens) that share their habitat. Crows and jays hate owls even more. The animosity is deserved — screech-owls prey on sleeping songbirds — and in response to an owl call, real or imitated, given during daylight hours, other birds will often converge to harass their enemy. Birders put this habit to use, employing owl calls to draw in other birds for observation.
In addition to songbirds, a screech-owl will eat nearly anything it can squeeze and bite into submission. Mice are probably their favorite prey, and what they are optimized to catch (screech-owls are undoubtedly a major force controlling numbers of white-footed mice, which host deer tick nymphs and serve as a reservoir for Lyme disease). But studies have shown that screechers can kill birds as large as themselves, presumably bushwhacking them in the dark. And in the warmer months, screech-owls prey heavily on large moths and beetles, frogs, salamanders, and small snakes as well.
On sunny days, screech-owls can be seen roosting in the mouth of their nest cavity, or perched next to a tree trunk, where their intricately barred plumage helps them blend in (these birds come in two basic colors, reddish-brown and gray). But unless you stumble over such a roosting bird, it takes a little effort and a lot of alertness to know that an owl is around. Pick a quiet night, brave the cold, and listen. They're out there.