Lifestyle

Bald Eagle


A bald eagle perches in a tall white pine while using its binocular vision to spot fish in the river below.

 

Do you get excited when you see a bald eagle, our national symbol? You will find them in many locations in the Great Lakes Bay Region. In fact, the bald eagle population has recovered enough in our state that it was removed from the list of endangered species in Michigan.

Identifying an adult bird is easy since we often see pictures of bald eagles. Adults have a black body with white head and tail feathers. “Bald” refers to the white feathers. The hooked beak, feet, and eyes are yellow. Juveniles have dark eyes and dark brown body feathers with white mottling on the underwing and belly. After each molt, juveniles’ plumage becomes so variable that it is difficult to accurately age them in the field. They do not acquire adult feathers until they are 4-5 years old.

When flying, an eagle’s wings appear flat or horizontal from the body, as compared to a turkey vulture that carries its wings in a dihedral and seems to teeter on the wind like a kite.

In winter, bald eagles stay near open water areas where they can hunt for fish or waterfowl. Groups of adult and immature eagles may share tall trees for nightly roosting. Many migrate to the Atlantic Coast, the southern Mississippi River corridor, or to the Gulf of Mexico coastline.


An adult eagle is surprisingly camouflaged in its natural habitat.

 

By March or April, eagles migrate north, and you may observe breeding behaviors. Courtship includes spectacular cartwheel displays as a pair of bald eagles locks talons, careens while falling, and then separates at the last minute before reaching the ground. Considered monogamous, a bald eagle pair mates for life unless one dies, though this is not well documented from the study of banded birds.

Eagles choose a tall pine or deciduous tree near a river or lake to build a big platform nest, usually 20 or more feet high. The bulky stick nest may spread 5 feet across and be over 3 feet deep. If a mated pair successfully raises young, the two bald eagles will return in subsequent years to reuse the nest, adding more branches each spring.

With only one brood per year, both parents take turns incubating the two eggs for 34-36 days and then feeding the nestlings until they fledge 70-98 days after hatching. Though fish dominate the bald eagles’ diet, they also eat small mammals and ducks or scavenge on fresh carrion.

Thwarting Threats

 

The bald eagle population is steadily growing. Listed as an endangered species in 1978, the bald eagle population has slowly recovered due to several factors. Recovery is attributed to the stoppage of agricultural use of the persistent insecticide DDT, which caused reproductive failure due to eggshell thinning. The protection of the eagles’ nesting habitats, the reduction in persecution by hunters, and a healthy food supply also have been beneficial to increased population. In 2007, the U.S. government delisted bald eagles from the national endangered species list, and the state of Michigan followed in 2009.

The Bald and Golden Eagle Protection Act of 1940 still protects eagles by prohibiting anyone without a permit from taking an eagle, taking or disturbing its nest, or taking its eggs. During breeding season (April to July), people must stay 330 feet (100 meters) away from nests. This includes recreational pursuits such as hiking, biking, bird-watching, camping, hunting, canoeing, and off-road vehicle and motorized watercraft use. Disturbance leads to nest abandonment or egg-hatching failure.

Threats still exist. Vehicles injure eagles that are eating roadkill along highways. Eagles can suffer from lead poisoning, acquired from food sources that have picked up lead shot or fishing tackle lost in the water. Other environmental pesticides, oil spills, and collisions with towers affect eagles’ health and longevity as well.

There are a number of locations close to home for eagle-watching. Nearby places to see eagles include Whiting Overlook Park in Midland, Shiawassee NWR in Saginaw, and the Saginaw Bay Birding Trail sites in Bay and Tuscola counties.

By Jeanne Henderson, interpretive naturalist

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