A Remarkable Migration

In late autumn, as temperatures drop and the leaves fall, a strange sound can be heard after dark in a few places around the Eastern Shore. It's a high-pitched, repeated "whoop" - the call of the Northern Saw-whet Owl (Aegolius acadicus). The sound is actually from a CD used as a lure to capture this tiny species. Generally, these owls don't make a sound outside of the breeding season. Each fall, thousands of the owls migrate down the coast to their wintering grounds.

So who would want to capture these owls, and why? Fletcher Smith, working for the College of William and Mary, is the bander in charge. The Cape Charles banding station is also part of a network of stations wound the United States participating in a program called Project Owlnet. Basically, their goal is to learn more about this secretive owl species.

The Northern Saw-whet Owl is named for the call given when it is alarmed. The "skiew" sound of the call bears resemblance to the sound of whetting a saw. The owls, hunt mainly at dawn and dusk, using low perches to drop down on unsuspecting prey. Prey species include mice, shrews, voles, small birds, frogs and insects. If prey is abundant, they may kill several prey items at once and cache extra prey in a safe place. When they are ready for the next meal, they will thaw out the prey by "brooding" the carcass. Like other owls, Saw-whets eject pellets composed of the fur, feathers and bores of prey species.

Northern Saw-whet Owls are found in coniferous and deciduous forests and prefer wet habitats. They are cavity nesters, often occupying cavities constructed by woodpeckers. These owls weigh about as much as a robin (around 3 ounces) and aren't much bigger than an average adult's clenched fist. Saw-whets are the smallest owls in the eastern U.S. The small size combined with their secretive nature makes them a difficult bird to observe. Many birders consider a glimpse at a Saw-whet a once in a lifetime opportunity. Fletcher Smith gets an up close look at several of these birds nearly every night.

Fletcher is following a netting protocol developed by Project Owlnet to coordinate the efforts of banding stations across the United States. Each night, before sunset he opens sets of mesh mist nets in several wooded habitats around the Eastern Shore. He starts an audio lure, which plays a series of Saw-whet calls. Fletcher makes his rounds to the different sets of nets all night long, extracting the birds from the net, banding them and taking a variety of measurements before they are released.

Age of the birds is determined by the stage of wing feather molt. The majority of birds captured are hatch-year birds, or those born that year. Sex of the birds is determined by differences in weight, wing and tail measurements. Females of this species are larger than males but are identical in appearance. This information is valuable for researchers to better understand Saw-whet Owls and their migration.

What have the researchers learned so far? Fletcher says, "We have learned that Saw-whet Owls are much more common in Virginia than previously thought." He averages about five owls each night, but overall numbers are lower this year. Banding stations across the U.S. are reporting a decrease in capture rates as well. The lower numbers are probably just part of the natural "boom and bust" cycle as the numbers reported vary every year. But continued monitoring is valuable to detect any major changes or possible problems with this species. If numbers would continue to decrease for several years, it could indicate a problem.

Another important aspect of this research, involves where these owls are going. In the east, the Saw-whets range is more northern, stretching into Canada. During migration, some owls move south but how far is not certain. "Some of the owls we capture winter here," says Fletcher. "Others may move south but there aren't many stations south of here. There is still a lot we don't know." Most of the birds recaptured at the local station are from Cape May and Assateague. Some birds banded here have been captured in North Carolina. When information from all the banding stations gets put together, a clearer picture begins to form. Researchers are continuing to discover more about these tiny owls, with the hope that a better understanding will lead to better conservation efforts for this species. If you would like to learn more about Project Owlnet, visit:

http://www.projectowlnet.org

Trina Morris
ESVNWR Intern