Editor’s Note: This story by Claire Potter first appeared in the Valley News on Dec. 17.
QUECHEE — Rehabilitators at the Vermont Institute of Natural Science are used to seeing injured barred owls arrive for treatment. After all, the raptors are abundant and unafraid of people. But some years, the number of barred owl intakes double, and many arrive half-starved.
“Some are just skeletons with almost nothing left of them,” said Bren Lundborg, the lead wildlife keeper at VINS. In the winter of 2019-20, nearly a third of the barred owls brought to the VINS clinic arrived emaciated, he said.
Naturalists had a hypothesis: In winter, barred owls hunt with their ears, jumping to attention when they hear a rodent rummaging under the surface of the snow. Then they plunge at the hidden prey and capture their food. But in warm, wet winters, a thick layer of ice crusts over the snows, and it could wall the owls out of reach of their food.
In search of a definitive answer, wildlife rehabilitators at the Quechee nature center partnered with Mike Anderson, a self-styled “number cruncher” at the SAS Institute, an analytics software company. He became a lifelong raptor aficionado when he read “My Side of the Mountain,” an adventure novel about a boy and his peregrine falcon.
He used 18 years of weather data from the Killington Ski Resort and records from VINS to paint a picture of what a bad year for the owls looked like. His findings, which they hope to publish as a research paper, confirmed the hypothesis.
In a bad winter for the barred owl, temperatures never sank as low as they did in other years, instead hovering closer to freezing. It snowed early in the year but rained more than normal, so ice layered into a thick crust over the snow.
Under these conditions, the number of intakes of barred owls was “almost double base level,” Anderson said. Weakened by starvation, barred owls struggle to recover from any injuries, compete with other predators and fend off disease. They also reproduce less successfully and young barred owls, unused to hunting for themselves, suffer the most. Other owl species, such as great grey owls, that also plunge into the snow to hunt may also suffer, he said.
A bad year for barred owls has consequences for people. The brown and white striated raptors are adaptable. They do not shy away from hunting near people, and they learn to hunt in a human-altered landscape, Lundborg said. And when desperate, they can be aggressive.
“Last winter, they were hunting at bird feeders when food was scarce,” Lundborg said. There, they could pursue the rodents that scavenge for fallen seeds.
One was so desperate that it attacked a chicken right in front of a person. At 1.5 to 2 pounds, they are too small to threaten most pets, he said. But desperation takes other shapes too. VINS treated another barred owl whose stomach was filled with the exoskeletons of caterpillars it had eaten when it could not find anything else.
Climate change will likely make the winter conditions that spell starvation for barred owls more common, VINS employees said.
“Predicted changes to regional weather patterns in Vermont and New England forecast that cases of malnourished barred owls will only increase in frequency over the next 20 to 30 years as we continue to see unusually wet winters,” Anna Morris, the lead wildlife educator at VINS, said at a presentation on the topic last year. “This study shows yet another way that climate change is currently affecting the health of wildlife species around us,” she added.
Still, barred owls are not at risk of extinction. Their population increases each year as more forests regrow and age across the region, Lundborg said. They thrive in old forests where they can nest in the hollows of old and gnarled dead trees.
But barred owls are not the only species to face a changing winter climate they have not adapted to.
Data from the Environmental Protection Agency shows that more and more birds have changed their migration patterns. Between mid-December and early January, 305 widespread North American bird species moved northward by 40 miles, with some shifting north by as many as 200 miles. And birds are not the only animals that move north: Parasites carrying novel diseases, such as avian malaria which now spreads among loons, bring new threats to New England’s birds.
The loons that spend their summers in New England also linger longer when temperatures are slow to drop, Lundborg said. But they need a large expanse of open water to take flight. So if the ice forms quickly, it can lock them into a small patch of open water with no way to escape.
