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Saw-Whet Owls: Iowa's Mysterious (and Tiny) Winter Visitor

  • 2/13/2015 5:29:00 AM
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Learn about Iowa's smallest owl, the saw-whet, from Iowa Outdoors magazine By Ty Smedes
From the January/February 2014 issue of Iowa Outdoors magazine

As a symbol of wisdom and mystery, many ancient cultures considered the owl ruler of the night and seeker of souls—guardian of the underworlds and protector of the dead. Regarded with great curiosity and fascination within our own culture, the mystique continues today.

Where do they come from? What migration routes do they follow? Why do individuals often choose new wintering sites from year to year—and often hundreds of miles apart? The secrets of northern saw whet owl migration are coming to light, and an Iowa research effort is contributing greatly to understanding this mysterious winter visitor.

It’s early November and I’m accompanying the trapping team, making our way along a ridge-top deer trail in the darkness. Headlamps illuminate the narrow pathway as we wind our way to where mist nets are strung between poles along the crest of a hill. We check the first side of the “L” shaped net configuration and—nothing. The second side of the net is a bit lengthier, and when it appears we will reach the end in disappointment, a tiny ball of brown and white feathers dangles within a fold of the nearly invisible netting. We’ve caught our first saw whet owl of the evening—a tiny migrant from the far north—weighing no more than about 4 to 5 ounces.

The location is Hitchcock Nature Center, nestled among the Loess Hills of southwest Iowa’s Pottawattamie County. Our team leader is Jerry Toll, master raptor trapper and research biologist. His assistant is Sandy Reinken, a vet tech. Both possess expert skills in handling birds of prey. It’s their fourth year trapping and banding saw whet owls, and Toll’s goal is to add to the body of knowledge from multiple trapping efforts across the country. He wants to determine the timing of the fall migration, and if a migration corridor exists along western Iowa’s forested Loess Hills.

According to the Cornell Lab of Ornithology, little data exist on population trends, and as Iowa’s first ongoing saw whet banding effort, all information recorded is pioneering science within our state. A cavity nester, this tiny owl likes to use old woodpecker holes, and favors forested areas where it hunts mice and some small birds. Heavy snow cover and extreme winter weather force northern saw whets to migrate southward from their primary habitat in Canada and northern tier states to a more favorable winter climate with increased availability of prey. Consequently, great numbers find Iowa’s milder winters with abundant prey to their liking. Our larger great-horned and barred owls are more conspicuous, but it takes a keen-eyed birder to find a tiny saw whet on its daytime roost, most often tucked close to the trunk of a cedar tree. As the smallest owl in eastern North America, it can be difficult to locate among the shadowy boughs of a conifer.

The Capture Method  
Toll begins trapping in mid-October, when migration is in full swing, and continues at the rate of four to five nights per week until mid-November. Nets are raised just after dark. Researchers often don’t quit until late evening. An audio device lures birds to the net, and although a springtime mating call is used, it draws curious birds in. The MP3 player is hung near the halfway point of the line of nets, and a recording is played at about 110 decibels, loud enough to be heard throughout the hilly area. The mist nets are constructed of very fine monofilament, which an owl can’t see in the darkness, and are stretched to within a foot of the ground to ensure even low-flying birds are caught. Although it can often take a few minutes to free an entangled bird, they are unhurt by the experience.

Processing the Captures
Toll and Reinken quickly free the tiny predator from the net, and transfer it to a cloth bag. They make their way back up the winding trail, to the park maintenance building, which serves as owl trapping headquarters each evening. Lining the workbench are a saw whet trapper’s tools. A caliper is used to take measurements of the beak and talons, and the wing cord and tail are carefully measured with a small ruler. A pair of specially designed banding pliers lay next to a wire loop containing scores of numbered leg-bands.Toll carefully inserts the owl into a small can (head first) for weighing. The snug confines of the can are a perfect size and ensure the bird’s wings stay secured along the body, preventing a struggle and chance of injury. The dark confines also quiet the bird. The can and bird are placed on a scale, and the pre-determined weight of the can is subtracted from the total weight to arrive at the bird’s weight. Weight is used as a factor in determining the sex. Females are substantially heavier than males. This bird’s weight (92 grams), along with a lengthy wing cord, indicate it is a female.

A distinction between hatch-year and adult birds is figured using ultraviolet light to age the wing feathers. Feathers of a hatch-year bird will fluoresce differently than those of an adult, since the age of replacement feathers is different. The room lights are turned out, and Toll holds the bird’s wing away from its body. The UV light indicates the tell-tale feather pattern of an adult. He then uses the banding pliers to carefully attach a numbered, aluminum band to the bird’s leg. Lastly, the bird’s wing-pit is carefully examined.

“Birds, including raptors, store fat, which they use for energy during migration and lean times. One place they store fat is in the wing pit. Since their skin is translucent one can see a fat deposits under the skin,” Toll explains. “Once fat deposits are used up, they begin to break down muscle tissue. We use a scale of zero to three to evaluate their present condition in conjunction with a measure of the amount of muscle mass on either side of the breastbone using a scale of zero to two. We use these measurements just to get a feel for a bird’s general health.”

At season’s end, all data will be passed to the U.S. Geological Survey’s Bird Banding Laboratory where it is processed along with information from other saw whet banding stations throughout the U.S. and Canada. Such data is used to determine population and migration trends, as well as adult to juvenile ratios and more.

When processing is completed, the diminutive owl is placed back into the cloth bag and taken outside. Left in total darkness for 10 minutes, her eyes will adjust back to the nighttime environment. Then the bag is opened, and the owl silently disappears into the night, none the worse for wear.

From Duluth to SW Iowa
During the fall 2012 trapping season, 69 saw whets were captured at Hitchcock and 13 more were banded at two other locations in the Loess Hills—Waubonsie State Park and the Loess Hills State Forest, placing the total for the southern Loess Hills corridor at 82 birds captured and banded during fall 2012. Three saw whets banded near Tofte, Minn. were recaptured at Hitchcock (nearly 600 miles to the southwest), along with two that were banded near Duluth. But the recapture that left everyone scratching their heads was the owl banded near Milwaukee, Wis. and recaptured at Hitchcock the next fall—spanning 500 miles across two states.

Looking To the Future
“Owl banding is a voluntary effort, although a small grant does pay for some equipment. Continuation of the project is dependent upon future funding and our findings,” explains Toll. “During the fall of 2011, a volunteer tried an evening of saw whet trapping in Ringgold County, with Reinken’s assistance. They caught four owls at the Mount Ayr Wildlife Management Area the first night of trapping. Following that successful effort, another trapping operation began during the fall of 2012.

“I would also like to initiate Stable Isotope Analysis of individual birds. Stable Isotope Analysis allows the researcher to examine a feather to determine the latitude of the bird’s natal area (where it fledged), based on what the bird ate as a hatch-year bird. When I ponder what we are doing, it becomes a humbling experience. We cannot help the individual raptor in their journey but perhaps what we are learning about them will help mitigate some of the conflicts of raptor-human interaction,” says Toll.

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