October 2017

Vol. 45, No. 5

Nonbreeding Vocal Repertoire of Northern Saw-whet Owls

Tim Spahr

Northern Saw-whet Owl. Photograph by Kristina Servant (CC BY 2.0).

General Information

Northern Saw-whet Owls are common across a large portion of North America. In the breeding season, they range from southeastern Alaska down through the mountainous terrain of the western United States, including southeastern Arizona. There are even resident populations in the mountains of Mexico. They also breed across much of the boreal forest in Canada, and down into the states adjacent to the Great Lakes and into the higher peaks of the Appalachians. In the interior west, they breed commonly in the Rockies. Saw-whet owls preferred breeding habitat is coniferous forests, but they also breed near bogs, forest clearings, and in deciduous forests.

In the nonbreeding season, Northern Saw-whet Owls will often retreat from the coldest climates, working their way south—and lower in elevation—into the mid-southern states such as North Carolina, Tennessee, Missouri, and Kansas. They can be surprisingly common south of the breeding range after a highly successful breeding season, and will often show up in a variety of habitats from swamps and field edges in the east, to riparian corridors and dry canyons in the west.

Among our smallest owls, Saw-whets are slightly longer and a bit more massive than American Robins. They prey almost entirely on small rodents, but will occasionally eat insects, small birds, and amphibians. Strictly nocturnal, they can be extremely hard to find in daytime roosts, or at night unless vocalizing frequently. Separating them on sight from other owls is straightforward generally due to size, although they can be confused with Boreal and Elf owls. Boreal Owls are slightly larger and have a prominent black outline around the face; this is brownish in the Saw-whet. Boreal Owls also show spots on the forehead and crown, while the Saw-whet will show streaking. Elf Owls are considerably smaller than Saw-whets and generally show a darker face with white concentrated above the bill and in the lores and eyebrows. Lack of ear tufts will allow easy separation from screech-owls (Canning, Rasmussen, and Sealey 2008).

During the winter of 2016–2017, large numbers of Northern Saw-whet Owls were observed in east-central Massachusetts. In particular, the areas near Lincoln, Sudbury, and Marlborough had high numbers of wintering birds. Banding results from peak migration in October and November at nearby areas—including Mass Audubon’s Drumlin Farm Wildlife Sanctuary in Lincoln—also showed large numbers of these owls. With so many birds at local hot spots, this proved an exceptional year for studying the extensive vocal array displayed by Northern Saw-whet Owls on their wintering grounds.

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