Like most birders we could probably count on one hand the number of northern saw-whet owls we have seen in the wild. Sure, we’ve heard quite a number of them giving their repeated “toot-toot-toot” whistles that sound remarkably similar to the sound we now come to think of as the warning that a truck is backing up.

Saw-whet owls are tiny—small enough to just about hold in one hand, and they are active almost exclusively at night. They tend to roost in thick, dark coniferous trees or tree cavities. So, good luck seeing one, right? Indeed, all of this makes saw-whet owls unlikely to be seen by the average bird enthusiast on an average birding outing. In fact, these habits have resulted in ornithologists knowing little about their biology, distribution, and movements.

Back in 1994, some owl researchers decided to try to do something about this lack of knowledge about saw-whet owls and started a collaborative owl banding project called Project Owlnet. Earlier bird banders had figured out that by putting out mistnets (those fine-threaded nets that look like extra-wide volleyball nets) at night they could catch migrating saw-whet owls. Even better, they found that if they played a tape of a calling saw-whet owl they could catch even more! Since that time, the Project Owlnet collaboration has grown to include 100 banding stations across the U.S. and Canada. Together, they have banded tens of thousands of saw-whet owls!

What is particularly amazing about these saw-whet owl banding stations is that in most places no (or very, very few) of the owls are ever detected by any other means, visually or by sound. Despite the fact that the little owls are attracted to the sound of a calling saw-whet, they never make a sound themselves during migration. Essentially, you have a bird that is invisible to humans unless you start banding them at night.

All of this is even more amazing when you find that in many places where no saw-whets had been detected previously, banding station researchers may catch dozens of them in a single night. Here in Maine there are or have been a number of saw-whet owl banding stations including one that was run for many years at the Wells Reserve at Laudholm Farms by our dear friend, the amazing bird bander June Ficker, who passed away last year. The Biodiversity Research Institute, based in Portland, has banded saw-whet owls at a number of locations along the Maine coast. Judy Camuso, a biologist with the Maine Department of Inland Fisheries and Wildlife, has banded saw-whet owls for many years in southern Maine. Another banding station, at Petit Manan National Wildlife Refuge in Steuben in eastern Maine, once caught 63 birds in a night! In Maine, the birds move through in largest numbers in September and October.

All of this northern saw-whet owl research has shown some interesting results. We now know that saw-whet owl populations, at least in the eastern U.S., exhibit a cycle in which numbers generally peak every four years, though that peak may be higher or lower at some times than others. We know that these birds truly are migrating southward in autumn rather than just dispersing in all directions as had sometimes been suggested. We know this now because we see birds banded in one location being recaptured farther south that same fall. Birds banded in Maine have been recaptured in New England, New York, even as far away as Virginia and Indiana. Some of the owls banded in Quebec have been recaptured in Maine on their way south.

With the onset of cooler weather, it’s probably a good bet that thousands of saw-whet owls will be migrating through Maine while we sleep—invisible except to all but a few researchers standing beside their nets in woods echoing with tooting whistles.

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology. Dr. Wells is one of the nation's leading bird experts and conservation biologists and author of the “Birder’s Conservation Handbook.” His grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, formerly of the Cornell Lab of Ornithology, is a senior director at the Natural Resources Council of Maine, a nonprofit membership organization working statewide to protect the nature of Maine. Both are widely published natural history writers and are the authors of the book, “Maine’s Favorite Birds” and the just-released “Birds of Aruba, Bonaire, and Curaçao.”