Bald Eagle

Bald Eagles

Bald Eagle

adult Bald Eagle

Text and photos by Dan Gleason, © 2009

From The Register Guard, March, 2009 Backyards Habitats

A Bald Eagle soaring overhead is an inspiring sight to birders and non-birders alike. It may always have been so, for this bird is revered in many Native American cultures and it inspired Congress to name it our nation’s national emblem in 1782. The Bald Eagle is a uniquely American bird, breeding only in North America. A few individuals may stray to Siberia during the winter but most spend their entire lives in Canada and the United States.

Of North American raptors, only the California Condor is larger than the Bald Eagle. There are larger raptors elsewhere in the world but none in North America. Bald Eagles can weigh from 6.5 to 13.5 pounds and have a wingspan of 5.5 to 7.5 feet. As with most raptors, females are larger, up to 25% larger in eagles. Size also differs with geographic latitude, and birds that breed in Alaska are larger than birds breeding in southern states. First-year birds also appear larger than adults because the flight feathers of the wings and tail are longer and more pointed, giving the illusion of greater size. The longer feathers help the young birds as they learn to fly and maneuver in the air, giving them more stability, an important consideration as they learn to hunt during their first year of life.

The solid white head and tail contrasting with the dark body, make the Bald Eagle easy to identify, but this color pattern is only found on adults that are at least 4-5 years of age. Younger birds are dark with varying amounts of white scattered over the wings and body. How much white and where it shows is a function of age, and immature Bald Eagles are often misidentified as Golden Eagles, which are rare west of the Cascades.

The Bald Eagle is certainly not a “backyard bird” in the same sense that a Black-capped Chickadee or House Finch is, but if you expand your definition, you won’t have far to travel to see one. Bald Eagles are found in Eugene and Springfield if you look for them along the river. Bald Eagles patrol the riverbanks from Mt. Pisgah to Delta Ponds and beyond in both directions. One pair has recently begun nesting in the Skinner Butte area. Fern Ridge Reservoir and agricultural fields north of town are also great places to look for eagles, especially in the winter when more of these birds can be found in the valley.

Bald Eagles are associated with water and are often thought of as fish-eating birds, and fish are an important part of their diet but their diet includes more than just fish. They are scavengers, feeding on dead fish, birds or mammals. During the winter, they often congregate in fields where sheep are being raised, and this larger number of eagles in the valley during the winter coincides with lambing season. Bald Eagles do not prey on live sheep but they are fond of sheep afterbirth and they will take any lambs that have died after being born. These are easy meals, requiring no hunting and are an easy size to feed on. Larger carcasses, such as deer or adult sheep, are difficult for eagles to open so they stand aside, letting Turkey Vultures make the first openings. Stealing food from others by harassment is also a common way for eagles to obtain their meals. Eagles will harass Osprey when both birds are in the same area. By chasing an Osprey that has caught a fish, the eagle hopes to get the Osprey to drop the fish, whereupon the eagle will swoop down to snatch the fish for itself. When these easier ways of obtaining food fail, eagles will hunt. They may swoop over a feeding flock of ducks or geese hoping to find a slow or weak individual that they can catch. They will also hunt small mammals and have been seen hunting rabbits cooperatively, where one bird drives the rabbit in the direction of another waiting eagle. But squabbling over food is more common than cooperation.

During the non-breeding season, Bald Eagles become very gregarious, especially if food is abundant, but they are much less social during the breeding season. It is often stated that eagles mate for life but there is little data to support this claim. In places where birds overwinter in their breeding area, such as here in Oregon, pairs do often stay together throughout the season and they likely form bonds that last several years. Eagles that wander long distances between breeding and winter grounds often don’t form long-lasting bonds.

Bald Eagles build the largest nests of any bird in the world. The large stick nests that you see prominently atop trees or light poles are the nests of Osprey, not eagles. An eagle’s nest is tucked down in the canopy of the trees, placed near the trunk on a sturdy supportive branch of a large tree, usually a conifer. Sticks and other material are added to the nest each year, often by successive generations of eagles, and the nest becomes very massive. The largest bird’s nest ever recorded was a Bald Eagle’s nest in Ohio which had been used for at least 50 years before it fell during a storm. It was estimated to contain nearly 2 tons of sticks!

Once young eagles have fully fledged and left the care of their parents, they begin to wander, often many hundreds of miles from where they were hatched. When it is time to breed, 4-5 years later, many of these birds will return to mate and breed not far from where they were raised. During the non-breeding season, many adults also wander, usually covering shorter distances than the younger birds. Our population of Bald Eagles greatly increases during the winter months, and in the Klamath Basin you can find the largest concentration of eagles anywhere outside of Alaska.

It is not safe to assume that all of the Bald Eagles that winter here are the ones that breed here or come from farther north. Young eagles raised in southern states frequently travel north to Canada and Alaska. Adults from these same areas don’t usually go as far but some may be found in northern California and Oregon. Birds that breed in northern California and Oregon generally tend to wander less and some of our winter eagles also remain to breed. Others may migrate only small distances. In fact, the shortest migration recorded for any bird was that of a Bald Eagle. It traveled only 268 miles from its winter grounds in Michigan to its breeding site in Ontario and it made this journey in less than one day.

The Bald Eagle’s return after severe population declines of the mid to late 20th Century due to pesticide use, is a much-publicized story and one I don’t have space to repeat here. Your opportunity to see these impressive birds is much greater now than it would have been 25 years ago. Take a stroll along one of the river bike paths and perhaps you will see a Bald Eagle sitting in an overhanging tree or flying over your head, giving you the same thrill that many others have felt.

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