SPECIES ACCOUNT
EASTERN SCREECH-OWL
(Otus asio)
Vineyard Overview: This small owl, a permanent
resident on the Vineyard, is undoubtedly the Island’s
most numerous bird of prey. No formal census has
ever been conducted, but screech-owls occur in a
wide range of settings on the Island, and our
population surely numbers in the hundreds of pairs.
The limiting factor determining where this species
nests is probably the availability of suitable cavities in
which they can nest (the species uses both natural
cavities, mainly in hollow trees, and artificial nestboxes). But while hunting, screech-owls can range
quite widely, and this is a bird you can hear or see
nearly anywhere on the Island. Screech-owls often
nest in surprisingly disturbed environments – a pair
or two is usually in residence in the Campground, in
Oak Bluffs, for example. So wherever you live, you
might well be surprised to find how close you are to
the nearest nesting pair of screech-owls.
The Eastern Screech-Owl takes prey ranging from
large moths or other insects to frogs to small birds.
But this species is best known as a hunter of small
mammals, including the meadow vole and the whitefooted mouse. Typically hunting from a perch at
night, screech-owls zero in on potential prey with
keen hearing and nocturnal vision, dropping onto
their prey with uncanny accuracy even in near-total
darkness.
Identification: About nine very plump inches long,
screech-owls strike most beginning birders as small
for an owl. This species has pale underparts with
heavy streaking. The head, back, wings, and tail can
vary widely in color, with most individuals either gray
Photo: Thomas Barnes/USFWS
Photo: Julian K. Robinson
or rufous (though intermediate colors also occur).
Among a screech-owl’s most striking features are
large yellow eyes and feather tufts resembling ears on
the top of the head. One other small owl occurs
regularly on the Vineyard (the Saw-whet Owl); this
bird lacks the feather “ears” of a screech-owl and is
much less common. So if you encounter a small owl
on the Vineyard, it is probably a screech-owl.
However, you are much more likely to hear than to
see one of these birds, and, happily, the normal calls
of an Eastern Screech-Owl are quite distinctive. One
call is a quavering whistle on a constant pitch;
another is a mournful, descending wail, also with a
tremulous quality. Screech-owls call mainly at night
(in particular, there is often a burst of vocalizing
shortly before dawn), but will sometimes call during
daylight, especially in response to a playback of a
recorded call (or to a reasonable imitation by a
whistling birder). While they can be heard at any time
of year, they call most during the fall and winter,
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when they are establishing territories and pair bonds
in preparation for their spring nesting season.
Ecological functions: Predators of all kinds play
an important role in controlling the populations of
the species they prey on. In the case of the Eastern
Screech-Owl, the prominence of small rodents in
their diet works out very well for humans: the whitefooted mouse is an important reservoir for the
microbe that causes Lyme Disease, and by helping
limit the population of this rodent, screech-owls
probably make significant contribution to human
health on the Vineyard. And both mice and voles can
cause economic harm by girdling small trees, a source
of damage that owls help keep in check.
Strategies:
1. Provide nesting sites. If you own woodland, you can
help screech-owls by leaving dead trees, especially
large ones, standing until they fall naturally. Holes in
decaying dead trees are the usual nesting site for
screech-owls. But screech-owls will also readily use
artificial nest boxes of an appropriate size and design,
and erecting one or more such boxes on your
property is likely to attract nesting owls.
While owls nesting under natural conditions
necessarily take their chances with nest predators,
people who erect boxes for owls can site the box and
put metal flashing on the tree or pole it’s mounted on
to help keep raccoons from raiding the nest.
2. Avoid diurnal disturbance. Owls, despite myths to
the contrary, are perfectly capable of seeing and
moving about in the daytime. But they are strongly
optimized for life in the dark, when their acute
hearing and remarkable night vision give them an
advantage over anything that threatens them (except,
of course, a larger owl!). If caught in an exposed
location during the day, screech-owls are vulnerable
to being mobbed or even attacked by crows and jays.
The result is, at best, a waste of time and energy by
the owl, or at worst, possibly injury at the hands of a
crow. So it’s best to avoid flushing an owl out of its
nest cavity or roost site during the day.
3. Maintain habitat. While this species is an
adaptable one, it does best in habitat that offers
plenty of nest sites and ample habitat for hunting.
Screech-owls do best in a mix of woodland and open
areas, such as fields or pasture. If you own a large
property, maintaining a mix of natural habitat types
will help provide with Eastern Screech-Owls with the
resources they need. And if you have a small property
that isn’t suitable for nesting owls, you can support
general conservation of the Vineyard landscape,
which benefits all of our wildlife.
Notes: The willingness of this species to respond to
recordings or imitations of its call makes the Eastern
Screech-Owl easy to observe, if you’re willing to make
a little effort. Imitating or playing their calls in a
suitable habitat (the edge of an open woodland is
ideal) often elicits a call from a real owl, and often
one or more birds will fly in to investigate. With a
flashlight, you can often get a good look as they perch
on a tree limb, observing you. If you know of a box or
cavity in which owls are nesting, you can often see
one of the adult birds peering out of the cavity’s
opening during the day.
Crows, jays, and many other smaller birds have a
strong animosity toward screech-owls (and indeed,
toward other birds of prey). If they find an owl
abroad in the daytime, they will mob it mercilessly.
Imitating a screech-owl call often draws other bird
species in to take a look – a technique that birders
frequently use to stimulate avian activity when the
birding gets slow.
Owls often display territoriality between species, as
well as among members of the same species. Larger
owls, such as the Great Horned Owl (rare but possibly
increasing on the Vineyard) and Long-eared Owl (a
rare, intermittent breeder here but more regular in
winter), will cheerfully kill and eat a screech-owl if
they get the chance.