The Crestone Eagle, December 2006:

The bald eagle

by Keno

The bald eagle is also known as the American eagle—Genus species: Haliaeetus (sea eagle) leucocephalus (white head). It is one of 59 species of eagles in the world, the only exclusively North American eagle, and is one of two eagles in North America, the other being the golden eagle.

The bald eagle is known as our nation’s bird, officially declared the national emblem of the United States by Congress in 1782. Its image and symbolism has played a significant role in American art, folklore, music and architecture.

This raptor is not really bald; it actually has white feathers on its head, neck, and tail.

The feathers of newly hatched bald eagles (called eaglets), are light grey, and turn dark brown at about 12 weeks of age. During their third and fourth years, bald eagles have mottled brown and white feathers under their wings and on their head, tail and breast. The distinctive white head and tail feathers do not appear until they are about 4-5 years old.

Bald eagles are about 29-42 inches long, weigh 7-15 pounds, and have a wing span of 6-8 feet. This makes them one of the largest birds in North America, and the largest of the raptors. Unlike most species, females are larger than males and the bald eagles that reside in the northern U.S. are larger than those that are found in the south. They have a life span of 20 -40 years in the wild, with reports of birds in captivity living to be 60 years old.

Historically, bald eagles were once very common throughout North America, from Alaska to Newfoundland, from Florida to California, and into northern Mexico. Their population numbers were estimated at 300,000-500,000 birds in the early 1700s. By the early 1960s their number fell to endangered levels of less than 500 pairs. This population decline was caused by humans, with such actions as the shooting of eagles, destruction of their habitat, contamination of waterways and food sources by pollutants, and use of pesticides on crops. For many years the use of DDT pesticide caused thinning of eagle egg shells, which often broke during incubation. This all played a role in harming our national bird and diminishing their numbers.

Strong endangered species and environmental protection laws, as well as active conservation efforts, have brought back the USA’s bald eagle population from the edge of extinction. The use of DDT pesticide was outlawed in the U.S. and this action has contributed greatly to the return of the bald eagle to our skies.

The number of bald eagles has increased so much that in June of 1994 the U.S. Fish and Wildlife Service proposed that they be downgraded from endangered status to the less urgent status of threatened, in all but three of the lower 48 states. There are now over 5,000 nesting pairs and 20,000 total birds in the lower 48 states. In Alaska there are over 35,000 bald eagles. Though still listed as a “threatened” species in the lower 48 states, but populations are healthy in Alaska, where half the bald eagles on earth live.

This species occurred as a vagrant once in Ireland. The poor exhausted bird was discovered by a national parks worker. Presumably, a storm blew it out to sea, and the eagle struggled across the Atlantic Ocean. The only bald eagle to be hatched outside North America was born on May 3, 2006 in a zoo in the German city of Magdeburg.

Bald eagles are seldom seen far from water—large rivers, lakes and seacoasts. They have a presence in every U.S. state except Hawaii. In Colorado they are often found near reservoirs, especially where there are abundant fish. Colorado had just one known nesting pair within the state in 1974; with 18 nesting pairs by 1993. This increased to 51 nesting pairs in 2001, and today there are between 60-80 nest sites and the increase appears to be continuing. Roughly one-third of the breeding sites are found east of the Continental Divide within the South Platte River watershed. Other breeding concentrations include the Yampa River upstream of Craig, the White River in the vicinity of Meeker, the Colorado River upstream of Kremmling, and the La Plata and Montezuma counties.

Bald eagles are monogamous and mate for life. They will only select another mate if their companion should die. They use a specific territory for nesting, winter feeding or a year-round residence. They build large nests, called eyries, at the top of sturdy tall trees. The nests become larger as the eagles return to breed and add new nesting materials year after year. Their new nests average 2 feet deep and 5 feet across. Eventually, some nests reach sizes of more than 10 feet wide and can weigh up to two tons. One nest was found that had been used for 34 years! The female lays 1-3 eggs annually in the springtime, which hatch after about 35 days of incubation. Hunting, egg incubation, nest watch, eaglet feeding and brooding duties are shared by both parents until the young are full size and strong enough to fly at about 12 weeks of age. Only about 50% of eaglets hatched survive the first year.

Eagles are carnivores and hunt during the day. They feed primarily on fish, but also eat small animals (ducks, turtles, rabbits, snakes, etc.) and carrion (dead animals). An eagle can spot prey from as far as a mile away, as they can see three or four times farther than people. They can carry their food off in flight, but can only lift about half their weight. They have been recorded at 44 miles per hour in normal flight, but their diving speed is estimated at 75-100 miles per hour. They can fly to altitudes of 10,000 feet or more, and can soar aloft for hours using natural wind currents and thermal updrafts. Plus, bald eagles can swim. They use an overhand movement of the wings that is very much like the butterfly stroke.

Bald eagles normally squeak and have a shrill cry, punctuated by grunts. They do not make the famous “eagle scream” which is often used and heard on television or in movies. What many recognize as the call of this species is actually the call of a red-tailed hawk.

Colorado is a very popular wintering area for bald eagles. In our area they are usually only around in the winter months—with about 100-200 bald eagles in the San Luis Valley on average each winter, depending on conditions both here and up north, where they spend their summers. The wintering ducks in the SLV are what brings them to this area.

Here in Crestone you are most likely to see them along Road T and Crestone Creek. According to Ron Garcia, manager of the Baca Wildlife Refuge, the best place and time of year to view bald eagles in the Valley is at the Alamosa Refuge, from mid-February until mid-March, where up to 150 bald eagles have been seen at one time.

Next month in the Eagle Part 2 will look at the golden eagle.