A bird and a puzzling sound lead to discovery

A bird and a puzzling sound lead to discovery

I walked around outside our Two Rivers home early one morning, as I sometimes do. It was mid-May and we - that's my wife, Julie, and me - were about ready to head to work.

The birds had recently returned. While waiting to get in the car, I heard American robins, black-capped chickadees, a ruby-crowned kinglet and a Swainson's thrush in our woods above Potlatch Creek. A raven flew over our sled dogs.

I know most of those bird songs, but I reached for my phone and its nifty bird-identification app anyway because it's fun.

Then came a song that surely was from a boreal owl.

Julie and I have heard it for several years. Everyone knows an owl sound. This one clearly qualified as hoot-ish.

The Cornell Lab's Merlin bird app disagreed with me that morning. It identified the sound as that of a Wilson's snipe, or Gallinago delicata by its scientific name. I tried the app again. Same result: a Wilson's snipe.

I ran to the house. "Hey, we have a new bird! Remember that sound we've long thought was a boreal owl? It isn't."

There was a bit of excitement.

Wilson's snipe are shorebirds. Ours must be enjoying the marshes of Potlatch Creek below us in a super shallow valley.

A little bit of research quickly informed us that the sound isn't a birdsong at all. It's the sound of some serious tailfeather action known as winnowing. It occurs in flight during high-speed courting or territorial displays and is mostly a feature of snipe.

"The Wilson snipe's outer tail feathers are the part that makes the winnowing sound as it vibrates," said Jack Withrow, bird collections manager at the University of Alaska Museum of the North. He's been the manager for about 20 years.

I had turned to Jack for some answers.

Jack took me down to "The Range," the museum's collections area housing banks of tall, wheeled cabinets, each holding numerous specimen trays. We stood in front of a cabinet he had just opened in one rolling wall. It included several meticulously placed and labeled birds of the genus Gallinago, which consists of 18 living species.

Jack carefully brought out and held two bird specimens, a Wilson's snipe and a common snipe, to show the stiff and sturdy outer tail feathers. Both species make the winnowing sound, but the Wilson's pitch is higher due to the feathers' narrower width.

Wilson's snipe breed across all of Alaska and nearly all of Canada. Common snipe only breed in some western regions of Alaska and the Aleutian Islands. The two were considered the same species until 2003.

"It's narrower on this bird," Jack said of the Wilson's outer tail feathers. "It's subtle, but you can see the common snipe as opposed to the Wilson's snipe has a broader outer tail feather."

It's so subtle that you'd need some calipers to discern the difference.

But what actually happens to make the winnowing sound?

Wind rushes over a diving snipe's outer tail feathers, vibrating them rapidly like the reed of a musical instrument. Those vibrations push and pull the surrounding air, creating pressure waves that we interpret as sound - the haunting winnowing.

Adam van Casteren of the University of Manchester detailed the aerodynamics of the common snipe's outer tail feathers in a 2010 research paper in the Journal of Experimental Biology. He wrote that the outer feathers can withstand great wind speeds.

George Sutton, a leading ornithologist of the early to late 20th century, described hearing the sound while in a boggy Pennsylvania woodland in April 1922.

"The hooting sounded like the rapid beating of wings," he wrote in a 1981 article in The Wilson Bulletin, a quarterly ornithology magazine. "At times it was so sudden and loud that it was almost frightening."

"For years I have pondered this remarkable hooting or bleating, wondering whether it has ever been explained fully and correctly," he wrote.

So Sutton went to work. He reviewed several studies and observations from the mid- to late 1800s, along with related drawings of snipe behavior and sounds. The earlier research offered ideas.

The tail feathers began to draw interest from those early bird experts. Sutton became convinced.

"Display flights are accompanied by hooting, bleating, neighing, or whinnying sounds that are widely believed to be nonvocal and that almost certainly are produced by vibration of some or all of the tail feathers," Sutton wrote nearly 60 years after his visit to the Pennsylvania marsh.

Let's get back to Julie's and my house and "our" Wilson's snipe.

I saw one zipping around above a snowmelt pond by our driveway recently and first thought it was a swallow. Its wings appeared sharp and angled in its zippy flight, similar to those of a swallow, but then I saw it land by the pond. It waded in a few steps and took some sips through its long, needle-like bill.

That, its coloring and its matchstick legs gave it away.

We learned a lot thanks to this tiny bird's owl-like sounds that rose from a nearby creek and traveled through the woods to our ears.

Ain't that a hoot?

Since the late 1970s, the University of Alaska Fairbanks' Geophysical Institute has provided the Alaska Science Forum column free in cooperation with the UAF research community.