Bald eagles are America’s pride

Bald eagles (Haliaeetus leucocephalus) in our area are becoming more common, especially near rivers, lakes and wetlands where these large birds find their favorite diet of fish.

Bald eagles mate for life, building nests near the tops of large trees. In this area, nests are found to be nearly 100 feet above ground. The mated pair typically returns to the same nest each year, adding to the nest, which often reaches 10 feet across and can weigh 1,000 pounds. New nests may be started when the nests grow very large, sustaining storm damage or breaking the supporting tree branches.

Females weigh to about 14 pounds and an 8-foot wingspan. Male bald eagles are smaller, weighing to about 10 pounds, with a 6-foot wingspan. Up to about age 3 or 4, the young are dark brown. When bald eagles reach maturity, at about age 4 or 5, the characteristic white head, mane and tail feathers appear. Both sexes have the same coloring, including yellow beaks, eyes and feet. It is considered the largest true raptor in the U.S. (the California condor, a larger, raptor like bird, is considered a vulture). The bald eagle is also unique to North America. They vary in size, with southern birds being smaller than birds living farther north. The bald eagle's life span in the wild is about 15 to 25 years.

These birds are early breeders, laying eggs from around the end of February to mid-March, with eaglets hatching after 35 days. Clutches of one to three eggs are typical, with an over 50 percent survival rate for young eaglets through the first year. Good survival rates for young and the long adult life span have resulted in the bald eagle increasing in numbers from past decline. The largest sibling has the best survival rate. Although females mainly incubate the eggs, males also incubate to allow the female to take time away from the nest. Both parents share in feeding and guarding the young and hunting for food. The preferred diet for eagles is fish, but they will eat other prey or carrion. Flying speed for a bald eagle is roughly 40 mph; about 30 mph when carrying a captured fish. In dives, bald eagles can approach speeds of nearly 100 mph.

The bald eagle was adopted as our national symbol in 1782, when it is estimated that approximately 250,000 to 500,000 nesting bald eagles existed. Hunting was indiscriminate, as they were considered predators of chickens, lambs and other livestock. Recognizing that bald eagles were declining toward extinction, Congress in 1940 passed the Bald Eagle Protection Act to help assure preservation. However, at about the same time, in 1939, the potent insecticide DDT (dichloro-diphenyl-trichloroethane) was discovered, achieving widespread use by the late 1940s. In 1948, the inventor, chemist Paul Mueller, received the Nobel Peace Prize, as DDT was considered a great boon to mankind in reducing diseases caused by mosquitoes and crop damage by other insects.

Also in the late 1940s, limited indicators started to emerge about terrible effects of DDT on wildlife, especially predatory birds that feed on animals which have taken in DDT from water supplies. A persistent chemical in the environment, one effect of DDT in birds is thinning of the eggshells, reducing the survival of the embryos. Since DDT traveled into surface waters, those birds with diets of fish and aquatic animals were the hardest-hit.

The U.S. Fish and Wildlife Service estimated in the early 1960s that less than 500 nesting pairs of bald eagles existed in the U.S. Rachel Carson's book "Silent Spring," published in 1962, galvanized public opinion toward correcting the decline of hard-hit native species. The first endangered species act passed in 1966, followed by listing of bald eagles as endangered in 1967. Recovery of the bald eagle population has been good, with the birds removed from the endangered and threatened wildlife listing in the lower 48 states in 2007. Current estimates are that over 100,000 bald eagles are now in existence.

Article by FCFCDB

Nature Notes for 4/7/2013