Scientists seeking insights into saw-whet owl migration

Nearly every evening between mid-October and Thanksgiving, when the weather conditions are promising for bird migration, Scott Comings sets up a series of nearly-invisible nets on Block Island and plays a recording of the call of the saw-whet owl, the smallest owl to be found in Rhode Island. His aim is to capture as many of the birds as possible, place bands around their legs, and learn what he can about the migratory habits of the diminutive owl.

            Comings, the associate director of the Rhode Island office of The Nature Conservancy, is among a growing cadre of biologists and ornithologists from throughout the coumtry who have been banding saw-whet owls regularly since the early 2000s to get an idea of the bird’s

Saw-whet owl (Megan Lorenz)

movement patterns and population distribution. The effort, dubbed Project OwlNet, began in Pennsylvania in 1997 and now includes several hundred researchers at more than 350 different sites.

            “Before this started, there was a big question about how they move through the area, so it became a concerted effort to see if we could crack this problem,” said Comings, who calls the birds “a really majestic species” despite being just 8 inches tall. “It’s a species that has always captivated me. It’s something you don’t normally see, so that pushes me to want to do more, to learn more, and to go deep into the night trying to catch them instead of sleeping.”

            Peter Paton, professor of natural resources science at the University of Rhode Island, is another of the Project OwlNet collaborators. He has been banding saw-whet owls since 2000 at locations in Richmond, South Kingstown and Hope Valley.

            “It’s as effective to set up the nets at my house as it is at more remote areas,” he said. “It turns out you can put a net out almost anywhere and still do a good job of catching the birds.”

            In a typical year, he catches more than 100 owls, and some nights when the winds are just right, he may catch a dozen or more in just a few hours. Comings catches similar numbers of owls, though one year he banded more than 200 of the birds.

            In the eastern United States, saw-whet owls primarily breed in northern New England and New York and in the Appalachian Mountains, and they winter as far south as North Carolina. According to Rachel Farrell, a member of the Rhode Island Avian Records Committee, saw-whet owls have been documented as breeding in Rhode Island just six times since 1952. Two of those records occurred in the last two years and were documented as part of the Rhode Island Breeding Bird Atlas, which is managed by ornithologist Charles Clarkson.

            “It seems like the species is maintaining a small but persistent breeding population in the state,” Clarkson said.

            But many more saw-whet owls migrate through Rhode Island. Those that are captured by Comings and Paton are revealing interesting details about their migration patterns.

            “We have a much better idea of their migratory pathways,” said Paton. “We’ve also learned that they’re much more common than people used to think. And we see an annual variation in their numbers.”

Paton said that the number of saw-whet owls migrating through the Northeast rises and falls every other year based largely on the number of acorns and other seeds produced by trees in the area. When trees produce large numbers of acorns, they provide abundant food for small mammals like mice and voles, whose populations then skyrocket. When the small mammal numbers increase, saw-whet owl numbers grow, because the owls eat the mammals and can produce more chicks.

Most of the owls caught in Rhode Island fly to the mid-Atlantic states.

“We know that because we’re starting to build a database of where the birds have been caught and where they’ve ended up,” explained Comings. “I’ve had birds I’ve caught recaptured by others in New Jersey, Massachusetts and Maryland, and I caught birds that had previously been banded in Cape May, New Jersey, and Massachusetts.”

Paton has similar records. “One year I caught a bird at my house in Richmond, the next year it was caught in northern Maine, and a week after that it was caught at Audubon’s Eppley refuge in West Kingston.”

One of the more unusual findings from Project OwlNet is that birds migrating for the first time often take a different route than older birds who have previous migration experience. First time migrants tend to be caught along the coast, while adult birds are more likely to follow an inland migratory route.

“The older birds know better when to fly; they’re a little more savvy,” Comings said. “If you’re an adult bird and this isn’t your first rodeo, you know to wait for a northeast wind, which takes you on an inland route. If you’re a young bird, you know you’re supposed to go on a north wind, but if it’s from the northwest it pushes you toward the coast. Almost all the saw-whet owls I catch on Block Island are young ones.”

So far, this year has been a quiet one for saw-whet owl migration. Through the first week of November, Paton had captured only one owl, and Comings hadn’t fared much better.

“It’s been really slow this year because the winds haven’t been right,” Comings said. “But there’s still time. I’m just waiting for that one big night.”

This story first appeared on EcoRI.org on November 16, 2017.