Winter poses a stiff challenge for birds that remain at our latitude through the season, and the vagaries of winter weather can produce sudden and obvious shifts in bird behavior. Island birders have recently documented many birds responding to the onset of real winter weather over the past few weeks.
The most dramatic sightings have involved two species of owl: barn and short-eared. The barn owl is a permanent resident on the Vineyard. Numbers have varied widely in recent decades, from zero to perhaps a couple of dozen pairs, with severe winters sometimes causing dramatic die-offs. The species is normally nocturnal, relying on sharp night vision and even sharper hearing to zero in on the small rodents that make up the vast majority of its prey.
But hard winters pose a double challenge to this species. For one thing, near the northern extreme of their range on Martha’s Vineyard, our resident barn owls are susceptible to cold. The birds are at risk of burning energy faster than they can take it in by feeding. In order to maintain a workable energy budget amid prolonged cold, barn owls need to eat more, which means they need to hunt more. When their usual nocturnal efforts don’t produce enough prey to balance the books, barn owls begin to hunt in daylight — first around dawn and dusk, extending their nocturnal work schedule in both directions, and then in broad daylight if the extended hours don’t suffice.
Even a modest snowfall adds another awkward twist. Barn owls on Martha’s Vineyard rely largely on meadow voles — plump, short-tailed, sausage-size rodents found mainly in open habitats such as pastures and grassland. Voles remain active under snow cover, trundling around in networks of tunnels as they go about their daily routine. Just a couple of inches of snow suffice to keep meadow voles submerged, and being hidden by the snow makes voles harder than normal for owls to capture. When it occurs, the combination of prolonged cold and snow cover puts our barn owls in a desperate situation: They must hunt almost constantly in order to take in enough calories to survive, and they must hope that their hunting is successful enough to counterbalance the increased energy expenditure of ceaseless flight.
The short-eared owl, a breeding species on the Vineyard until just a few decades ago, fares a bit better during severe winter conditions, simply because it’s better adapted. Most of the North American breeding range of this species lies to the north of us, in New England and across Canada. In winter, short-eared owls can be highly mobile, migrating short or long distances in response to weather and prey availability. Their wanderings occasionally bring them to the Vineyard in winter. Normally much more diurnal than barn owls, short-eared owls are commonly observed during the day. But the presence of this species on Martha’s Vineyard in winter probably reflects migratory movements undertaken in response to cold weather, or diminished foraging success farther north.
Beginning in late January and continuing at least into mid-February and the recent snowfalls, both of these owls species have been found regularly, and well-photographed by multiple observers. The first hint I can recall that something was up came on Jan. 21, when photographer Ray Ewing found a barn owl hunting at Quansoo in waning late afternoon light. A few days later, photos began coming in of at least one barn owl hunting during the day at Katama (a traditional site for both of these owl species). Jenny Kang and David Goldenberg both got great barn owl shots on Jan. 25, and through the first half of February, additional images continued to come in.
Short-eared owl reports seem to have begun around Feb. 1, when Jeff Bernier photographed this species at Katama, and since then, one or two birds have been found reliably there. Gretchen Lally has managed spectacular shots of both owls in recent weeks.
It is not just owls that are stressed by winter weather, of course. Songbirds face a similar challenge, with cold weather raising the energy requirements of their bodies, and snow cover, even just an inch or two, dramatically increasing the difficulty of finding seeds or overwintering insects to eat. The sudden need for new or more productive food sources can drive birds that were formerly quite content in natural thickets to explore other options, such as feeding stations. To cite just one recent example, a secretive yellow-breasted chat appeared, seemingly out of nowhere, at Wayne Jackson’s feeder in Edgartown on Feb. 9. As with the owls, increasingly dire conditions forced this bird to gamble with new, more exposed foraging behavior.
From the birdwatching perspective, episodes like these represent an opportunity for good looks at seldom-seen species. From the birds’ perspective, of course, it’s a different story: The fact that these birds are suddenly so easy to observe reflects desperation, as the birds address a life-threatening squeeze on their energy budgets.
