Birds have been referred to as “bellwethers of watershed health” because they respond to basic changes in landscape and habitat conditions.Roger Tory Peterson, an American naturalist who published many books about birds and garnered multiple awards in his field, once said, “Birds are an ecological litmus paper. Because of their rapid metabolism and wide geographic range, they reflect changes in the environment quickly, and they warn us of things out of balance, sending out signals whenever there is deterioration in the ecosystem.”
GLA’s Watershed Biologist Rob Karner, a former ornithology instructor, monitors the variety, patterns, and health of area birds as potential leading indicators of overall watershed health. The robust diversity and health of our year-round resident birds and migratory birds point to a healthy watershed, and we felt it was important to introduce you to some of them. We hope you have enjoyed our series — share it with friends and family so we can all be a little more connected to our beautiful watershed and the creatures that live in it.
The bald eagle has been the national emblem of the United States since 1782. These regal birds aren’t really bald, but their white-feathered heads gleam in contrast to their chocolate-brown body and wings. Once endangered by hunting and pesticides, bald eagles have flourished under protection. You may have seen bald eagles soaring along the south shore of Big Glen near Inspiration Point, on the north shore of Little Glen Lake, or along the Alligator Hill trail, among other local spots.
Fish of many kinds constitute the centerpiece of their diet – you may have been lucky enough to spot a bald eagle diving toward our lakes, only to pull up at the last second, grasping onto an unsuspecting trout with its razor-sharp talons. They eat a wide variety of other foods depending on what’s available, such as smaller birds, reptiles, amphibians, invertebrates such as crabs, and mammals including rabbits and muskrats. They take their prey live, fresh, or as carrion. Bald eagles sometimes gorge, ingesting a large amount of food and digesting it over several days. They can also survive fasting for many days, even weeks.
Bald eagles are powerful fliers—soaring, gliding, and flapping over long distances. In one of several spectacular courtship displays, a male and female fly high into the sky, lock talons, and cartwheel downward together, breaking off at the last instant to avoid crashing to earth. Bald eagles frequently harass birds including ospreys and other eagles to steal their food, and occasionally do the same to mammals such as river or sea otters. On the ground, bald eagles walk in an awkward, rocking gait. Capable of floating, a bald eagle may use its wings to “row” over water too deep for wading.
Bald eagles typically nest in trees and prefer tall, sturdy conifers that protrude above the forest canopy, providing easy flight access and good visibility. It’s unknown whether the male or the female takes the lead in selecting a nest site. Nests are typically built near the trunk, high up in the tree but below the crown. They build some of the largest of all bird nests—typically 5 to 6 feet in diameter and 2 to 4 feet tall and ranging in shape from cylindrical to conical to flat, depending on the supporting tree. Both sexes bring materials to the nest, but the female does most of the placement. They weave together sticks and fill in the cracks with softer material such as grass, moss, or cornstalks. The inside of the nest is lined first with lichen or other fine woody material, then with downy feathers and sometimes sprigs of greenery. Nests can take up to three months to build and may be reused (and added to) year after year.
Immature bald eagles spend the first four years of their lives in nomadic exploration of vast territories and can fly hundreds of miles per day. Some young birds from Florida have wandered north as far as Michigan, and birds from California have reached Alaska.