Northern Saw-whet Owl: Tiny traveler

How does one mark the coming of spring in a northern-tier state? By the arrival of Northern Saw-whet Owls, say Chris Neri and Nova Mackentley, owl banders at Michigan’s Whitefish Point Bird Observatory (WPBO).

More than 330 species — Spruce Grouse, Rough-legged Hawk, Boreal Chickadee, Black-backed Woodpecker, Great Gray Owl, Northern Hawk Owl, and others — have been recorded at Whitefish Point. Jutting from the Upper Peninsula of Michigan into the extreme southeastern end of Lake Superior, the promontory acts as a natural funnel, concentrating birds that fly along it into an ever-smaller area.

Each year, researchers at WPBO, an affiliate of Michigan Audubon located at the peninsula’s tip, monitor the migrations, tallying tens of thousands of birds. They have found something surprising about the movements of the nocturnal saw-whets — that the best time to record them is spring, not fall.

To learn more, Neri and Mackentley trudge through Whitefish Point’s snow banks, which often last into May. In March 2013, Neri arrived for his 24th saw-whet-banding season, Mackentley for her 18th.

“As always,” said Neri on opening night, March 15, “we’re thrilled to be starting another season at WPBO. But there are usually several feet of snow on the ground, making it difficult just to walk, let alone trap and band tiny raptors like saw-whets.”

Opening night the previous year (2012), he said, saw rivers of snowmelt, bare ground, and 95 owls banded. “But it’s not like that this year.” Neri and Mackentley would be cooling their heels for some time before the first owl of the season. “With this cold weather, we may be paying some dues before migration kicks in,” said Neri.

From 1988 to 2006, spring owl banding ran from April 1 through May 31. In 2007, the start date changed to March 15; researchers found that saw-whets had started migrating north from wintering to breeding grounds by mid-March.

It was a harbinger of results to come. WPBO scientist Josh Van Buskirk, now at the University of Zurich, discovered that changes in the timing of spring migration are happening in many raptors that pass through Whitefish Point. He published the results in a 2012 paper in The Auk, the journal of the American Ornithologists’ Union.

“Spring migration in the Northern Hemisphere is occurring nearly a week earlier than it was 30 years ago,” said Van Buskirk. Birds overall are spending more time in northern climes — by up to 30 days — than they were in the early 1970s. Birds of prey are arriving earlier and leaving later.

March 25, 2013. Nature is nothing if not unpredictable. The first owl of the spring season is finally caught. “We weren’t expecting it to be a Boreal Owl, a close relative of the saw-whet,” yelled Neri into wintry winds that howled across the point. “But a Boreal it was.” On May 6, 1966, a Boreal Owl unexpectedly captured at Whitefish Point led to the owl research WPBO now conducts.

March 27, 2013. Several feet of snow still blanket the ground. “It will likely be a few weeks before it truly feels like spring,” said Neri, “but with a forecast high of 46 degrees [Fahrenheit] today, that’s a welcome start.”

He and Mackentley, however, still hadn’t caught a saw-whet. But the next night, the picture would change. “As of 2 a.m.,” said Neri, “there was still no sign that the owl migration would pick up. But half an hour later, we caught our first saw-whet of the season.”

Method to the madness

Is there a method to the madness of braving icy winds and blowing snows? How does one catch a Northern Saw-whet Owl in spring — or any time of year?

Neri and Mackentley and hundreds of other saw-whet banders across the U.S. and Canada hang 36-foot-long fine-mesh mist nets between two steel poles hammered into the ground. Owl calls — recordings of saw-whet hoots broadcast from speakers in covered plastic buckets beneath the nets — beckon like potential mates. Even sharp owl eyes don’t see the nets until it’s too late. Nets are checked four or five times each night.

Owls caught are carefully removed from the mesh and banded on one leg with a numbered metal ring from the U.S. Fish & Wildlife Service. Later, if a bird is re-trapped or otherwise found, the band will tell scientists something of where the owl has been. Each owl — and other raptor — species needs a band that fits its leg size. For saw-whets, which are only about eight inches long (18-21.5 cm) and weigh about as much as a robin, that’s a very small band, indeed.

Among the smallest owls in North America, saw-whets eat primarily deer mice, voles, and other rodents, but birds, taken mostly during migration, make up a small part of their diet.

In spring and summer, the owls breed in the coniferous forests of southern Canada and the northern U.S., nesting in tree cavities, especially abandoned woodpecker holes. In late fall, saw-whets fly south along two major corridors, the Atlantic coastline and the Ohio River valley, to the mid-latitudes of North America. The exact limits of their winter range are not well known.

The farther north an owl summers, the sooner it lights out for points south come fall. In eastern Canada, for example, saw-whets are moving by early to mid-September, reaching northern Pennsylvania in late September, central and southern Pennsylvania the first week of October, then making their way onward.

In spring, the owls head back north in a less concentrated, more fanned-out manner. One of the few places they’re seen in large numbers is at Whitefish Point.

Migration documented

The first owl bander to document the spring migration of Northern Saw-whet Owls was Canadian plant taxonomist Paul Catling, who described a March and April flight near Toronto in a 1971 paper published in the journal Bird-Banding.

“Spring [owl] migration at Toronto begins in late March, reaches a peak in mid-April and ends by late April,” Catling wrote. “The spring concentration of saw-whet owls along the north shore of Lake Ontario can be explained by a more or less direct crossing of the lake,” he believed. “A major influx occurs on clear nights when there are light winds. The period of spring migration may be related to the abundance of small passerine birds also migrating at that time.”

Before Catling’s research, few references to a spring saw-whet migration could be found. In 1914, New York state ornithologist Elon Howard Eaton wrote that he had seen evidence of an April owl migration along the Great Lakes. In 1952, Tom Barry stated: “Name your woodlot along the lakeshore [the south shore of Lake Ontario] and chances are that, during the first week of April, saw-whet owls can be found there.” In 1965, Clark Beardslee and Harold Mitchell discovered that at “the height of spring it is possible to find a number of saw-whet owls by checking woods and thickets along the south shore of Lake Ontario.”

To find out how extensive the migration was, Catling searched daily for saw-whets in Fallingbrook Woods near Toronto. At that time, in the late 1960s, Fallingbrook was a 10-square-acre forest of red oaks and hemlocks. The Lake Ontario shoreline formed its southern boundary. Catling combed the woods each day in March and April of 1968, 1969, and 1970 and found owls only in late March and during the first three weeks of April. Seven were banded in 1968, 16 in 1969, and 12 in 1970.

In March and April, Catling stated, many small passerines are also on the move. “Especially notable is the abundance of Black-capped Chickadees, Winter Wrens, Brown Creepers, Golden-crowned Kinglets, Ruby-crowned Kinglets and Hermit Thrushes.” Several of the owls banded at Fallingbrook grasped such prey when they were caught. Songbird remains were also in the owls’ pellets.

Catling compared his data with banding records from 1964 to 1969 from the Island Natural Science School on Toronto Island. “The results are strikingly similar,” he wrote. “The spring concentrations on the south shore of Lake Ontario are probably due to a build-up of owls awaiting suitable weather and sufficient energy to cross over the lake.”

More than 40 years later, scientists agree. “In fall,” says Bryan Watts, director of the Center for Conservation Biology of the College of William and Mary in Williamsburg, “Virginia’s Eastern Shore acts as the same kind of funnel, concentrating southbound Northern Saw-whet Owls and other birds.” Coastal forests just inland are a favorite saw-whet haunt. The owls stop by the piney woods, sometimes for as long as 10 days, before crossing the open waters of Chesapeake Bay. The behavior is not so different from how they use land’s end at Whitefish Point in spring.

Funnels for owls

Saw-whet migration — in spring and fall — is accepted knowledge now. But it wasn’t always so. Until the early 1900s, it was believed that the owls remained in their northern territories year-round. Then came October 1906.

The first days of the month were warm and damp, recalled naturalist W. E. Saunders of London, Ontario, reporting in The Auk. But on the sixth night, a north wind sent the temperature down to freezing, where “it stayed with little variation until the 10th. On the 10th the wind brought snow through the western part of Ontario.” Toward Lake Huron, snowfall reached 18 inches, and the temperature dropped well below freezing. “There must have been a heavy migration of birds across Lake Huron,” Saunders believed, “and the cold and snow combined overcame many of them, so that they fell in the lake and were drowned.”

A Mr. Newton Tripp of Forest, Ontario, spent the day of October 18, 1906, walking along the lakeshore. He found hundreds of dead birds cast up by the waves. Tripp calculated 5,000 birds per mile. Upon hearing of the tragedy, Saunders took the first train to the scene. He walked the beach for miles, finally coming upon what he called “the region of death.”

“At first the birds were not very close together,” he related, “but eventually became so plentiful that in one place I put my foot on four, and saw as many as a dozen in four or five feet.” Among the 1,845 birds Saunders counted were 24 that left him in disbelief: Northern Saw-whet Owls.

“The saw-whets were a surprise,” he wrote in The Auk. “Evidently they migrate in considerable numbers.” Saunders’s unfortunate find was the first scientific evidence of migrating Northern Saw-whet Owls.

During the following decades, new discoveries, such as Catling’s, were made about saw-whet migration. But understanding of the owls’ activities didn’t deepen until 1994, when raptor biologist David Brinker of the Maryland Department of Natural Resources founded Project Owlnet (www.projectowlnet.org). Since then, the project has grown from five banding stations in Maryland to a network of more than 50 from Maine to Alabama and as many again in Canada. Together, they catch and band 8,000-15,000 migrating owls each year, most in autumn but many in spring.

Project Owlnet’s goals are to support expansion of the network in North America; advocate the use of comparable netting protocols so results may be compared; and increase coordination of banding stations to help scientists uncover the intricacies of owl migration.

WPBO is a member of Project Owlnet and, according to Brinker, one of the best places to learn about Northern Saw-whet Owls’ spring migration.

Yellow eyes in flight

April 9, 2013. “We have seen the light at the end of the tunnel, and it has yellow eyes,” said Neri. He and Mackentley had a banner night. They banded 16 saw-whets and caught one that had been banded in Wisconsin in the fall of 2011. “We had just nine owls during the first three weeks of the season,” Neri said, “so we were happy to see the first real sign that owls were starting to head north.”

April 16, 2013. Saw-whet migration burst open. “The saw-whets gave us a run for our money,” said Mackentley. “We banded 99 and had four more that were previously banded.” One of the night’s owls had retained its juvenal plumage into spring. WPBO banders had seen this in only one previous spring.

May 4, 2013. “It finally feels like spring on Whitefish Point,” said Neri. He and Mackentley banded 105 owls over a two-night period.

May 16, 2013. High winds, blinding snow, and driving rain — a second winter — kept WPBO closed for three of the last six nights.

May 20, 2013. Neri and Mackentley had banded more than 700 Northern Saw-whet Owls, but the season was winding down. The forecasts now called for rain, not snow. “My winter hat and heavy fleece finally came off,” Mackentley said. “With the last of the migrating owls, spring may be here to stay.”

Postscript: July 20, 2013. Summer saw-whet monitoring, in its eighth season at WPBO, is underway. Summer owl monitoring? Neri and Mackentley had just banded the 2,000th juvenile Northern Saw-whet Owl as part of a research project to determine when young owls molt into adult plumage. That date may be much later than researchers thought.

“Discovering something new about saw-whet biology is a rare experience,” said Neri. “We didn’t know what to expect when we first opened the nets in the summer of 2006, but we didn’t think it would result in banding 2,000 juvenile saw-whets in this short time period.”

Northern Saw-whet Owls may zero in on the point as much in summer nesting season as they do in spring migration. “We’ve learned never to underestimate Whitefish Point,” said Neri, “or Northern Saw-whet Owls.”

 

Originally Published April 1, 2014