There is something wonderful about an autumn night; the sharp bite to the air, the rustle of a north wind in the last leaves clinging to the tops of the oaks, Orion shining in a moonless sky over the central Appalachian ridges of Pennsylvania—and echoing over it all, a repetitive, mechanical beep that reminds most people of the warning alarm when a garbage truck is backing up.
That sound—in this case, an audio recording played through a pair of bullhorn speakers—isn’t automotive. Instead, it’s the toot-toot-toot call of a Northern Saw-whet Owl, the male’s breeding song that’s used by scientists to lure migrating saw-whets out of the star-shot sky and into mist nets. I’ve spent close to a thousand autumn nights like this over the past two decades, in my work as a researcher capturing and studying this mysterious little bundle of feathers. Yet as I climb the lower slope of the ridge that leads to our nets, I’m still as excited as I was back in the 1990s, embarking on our studies of the unseen evening migrations of these most enigmatic raptors in North America.
One thing’s for sure, the hill hasn’t gotten any less steep in the past 23 years. But my companions and I don’t wait to catch our breath; shining our headlamps down along the line of nets, I can see three—no, four—small, gray-brown bodies cradled and wriggling in the mesh, and likely more around the corner where the remaining array forms an L shape. Someone flips a switch to turn off the audio playback, and the night goes silent as I reach carefully into the net and grasp the small, fully feathered feet of the owl to keep its needlelike talons out of my fingers. In a few moments I have slipped the owl free from the mesh.
Only the size of a soda can, a saw-whet is a diminutive raptor, but don’t mistake its wee size for a lack of moxie. This bird has fluffed out its feathers in a bid to intimidate the giant primate holding it, and is rapidly clacking its bill in a dead-serious threat as I slip the little owl into a lightweight cotton bag and cinch the drawstring tight. The owl snaps its beak once again and I glance down to see the tips of eight sharp, shiny black talons poking through the cloth as I move to the next bird.
By the time we head back down the hill to a little cabin, we have nine freshly caught saw-whets in cloth bags. The birds must be weighed, measured, sampled for blood and feather analysis, and outfitted with tiny metal leg bands—the latest additions to a continental monitoring effort that has solved some (but by no means all) of the mysteries surrounding this tiny bird of prey.
A Mysterious Little Owl Brought to Light
My first encounter with saw-whets in the hand came in 1996. The previous autumn Eric Atkinson—at the time a biologist at Hawk Mountain Sanctuary near my home in eastern Pennsylvania—had banded a stunning 80 saw-whets in his rural backyard with the help of his wife Melonie. They were trying what was then a fairly new approach using an audiolure recording, and their 80 owls in a single season astounded anyone who considered saw-whets incredibly rare—which was almost everyone.
In the mid-1990s, saw-whets were listed as a candidate species for state protection in Pennsylvania, a bird so infrequently seen that even the most avid birders I knew might go a lifetime without spotting one. So I was both shocked and very intrigued by the Atkinsons’ results. At the time, my consuming passion was banding hawks, falcons, and eagles on migration through the Appalachians—raptors that were trapped during the day. But I’d felt the first, seductive tug from the Dark Side with the Atkinsons on those autumn nights at Hawk Mountain, and after catching several saw-whets myself, I was hooked. By the next year, with some seed money from a small state grant, we had recruited a loose network of banding stations across Pennsylvania to target saw-whets.
I oversaw one of those first stations for the Ned Smith Center for Nature and Art, and that effort, now in its 23rd year of netting these little nighttime owls in central Pennsylvania, has become one of the largest saw-whet research programs in North America. With a team of 20 federally licensed banders and a total crew of nearly 100 people—all of us volunteers—working at three research sites, the Ned Smith Center stations have banded more than 12,000 owls and pioneered the use of a number of new technologies, including geolocators and nanotags, to study owl migration. Every rainless night from the beginning of October until after Thanksgiving we’re in the woods, stretching our nets into the midnight hours and playing that repetitive, garbage-truck call.
The bird at the heart of all this effort is still enthralling, but less of a cipher than it was two decades ago (and no longer listed as a candidate species in Pennsylvania, in part because of our work documenting it).
The Northern Saw-whet Owl is the smallest raptor in eastern North America. In our studies, larger females averaged about 96 grams, a little more than half the weight of an Eastern Screech-Owl and a bit less than an American Kestrel. Male saw-whets only averaged about 78 grams, but we don’t see many males.
One of the abiding puzzles about these birds is the dramatically skewed sex ratio at banding stations across their range, where females outnumber males three or four to one. Almost all of the males that are caught are juveniles making their first migration. Out of 12,000 or so saw-whets we’ve banded in Pennsylvania, only about a dozen—literally one in a thousand—have been fully adult males.
Where are the grown-up guys? There’s no doubt that our sample is biased to some degree because our audiolure is a male courtship call, which should be more attractive to females. (Though why female owls are attracted to a breeding call in autumn remains a puzzle.) Recent work by our colleagues Chris Neri and Nova Mackentley at Whitefish Point Bird Observatory in Michigan found that playing a female vocalization at one set of nets increased the male capture rate there; but they also found that females still dominate the sampled saw-whet migration overall.
A female bias in saw-whet migration could be explained by looking to Scandinavia. There, studies of the saw-whet’s closest relative, the Boreal Owl (or Tengmalm’s Owl, as it’s known in Europe), have documented adult males remaining in their northern breeding range through the winter. Perhaps (as with Boreal Owls) male saw-whet owls move widely and somewhat nomadically to find areas with high rodent populations, so they can establish territories and be ready when the females come back north. But so far this behavior remains a hypothesis awaiting confirmation.