Schiess: Rough-legged Hawks migrate to Southeastern Idaho

The migration of the winter hawks across the high desert between Mud Lake and Mountain Home were evident as my wife and I traveled to Boise last week. The Swainson’s hawks that dominate the raptor population during the summer have moved on to Central America while the Red-tailed and the Rough-legged hawks have taken the Swainson’s perching spots.

One of the largest hawks, Rough-legged hawks are named because of the feathers on the legs to their toes. This is believed to protect the legs from the bitter cold temperatures. With their highly developed eyesight, they can see long distances. They have the ability to hover over an area like a kestrel, allowing them to hunt from a perch or while hovering.

Often these royal hunters are forced to feed on dead animals or road kills where they compete with eagles and ravens. Rodents are their preferred targets. On the snow, rabbits, mice, voles and other rodents are prime targets for these effective hunters.

One of my favorite winter activities is to travel the roads looking for divots in the snow where a Rough-legged had heard and successfully harvested a rodent. Their skill at hearing, hovering and then harvesting is unequaled.

Even with the mild weather, the Red-tails have migrated from the area forests and mountains where most of them nest, to hunt in the grassland, hay fields and low sage in the valleys of Central Idaho. Within the next three weeks, the Arctic-nesting Rough-legged hawks will show up with dozens perched on irrigation wheel lines, power poles and fence posts. Traditionally, Rough-legs are the most abundant winter raptor on the Idaho National Laboratory with over 100 of them spending the winter hunting the desert and surrounding agriculture fields.

Rough-legged hawks spend the summer nesting and raising their young above the Arctic Circle where they feed mostly on voles and lemmings. Often, caribou bones can be found as material used to build their nests. The number of eggs and chicks produced are in direct proportion to the abundance of prey available during the summer.

In September of each year, Rough-leggeds will start appearing in the open country on and around the INL. As winter sets in, the more abundant summer Red-tailed hawks are replaced by the arctic invaders.

Raptors are not designed for long migrations because of their broad tails and wide wings. For this reason they migrate by soaring along mountain ridgelines where updrafts keep them aloft. With several large mountain ranges ending at the Arco desert, this area is a perfect place for these Rough-leggeds to migrate to.

Raptors are near the top of the food chain and watching them can indicate problems within an ecosystem. Since 1983 the INL has been conducting mid winter surveys of raptors. In 2006 during the count 288 Rough-leggeds were counted compared 28 other raptors. While the 2007 survey showed only 36 Rough-leggeds with 16 other raptors. Yearly fluctuations usually vary with a high count usually followed by a low count year.

In recent years a western states counting study, the East Cascades Audubon Society Winter Raptor Survey Project, of all raptors have been conducted in Oregon, California, Washington and Idaho. For three years I was part of that study where volunteers are assigned areas to count all raptors once each month from November to March. The Rough-leggeds continue to be one of the top three raptors in Idaho during the winter months.