The Audubon Society of Western Pennsylvania has kindly answered many questions from readers about the Pittsburgh eagle pair, and bald eagles in general. Watch the live cam and join the conversation at www.post-gazette.com/baldeagles.
THE BASICS: Eagles weigh between 8-12 lbs. with a body length of about 32 inches. Male eagles are slightly smaller than females -- adult females stand 35 to 37 inches tall, have a wingspan of 72 to 90 inches and can weigh 10 to 14 pounds; males weight about 20% less. • Bald eagles become mature in four years. • First-year birds have larger wingspans than older birds of the same sex because of their longer, “practice” feathers, which make learning to fly easier. • Eagle pairs typically mate for life and live for up to 30 years. • Bald eagles can fly as high as 10,000 feet. In level flight, they can reach speeds of 30 to 35 mph. •
HAYS PAIR: The Hays female is believed to be 5½ years old (as of spring 2014). • The Hays male is smaller and has a small white spot on his right side near the tail. • The eagles are in Pittsburgh because there's food here -- a sign that the town is cleaning up. In 1967, a Monongahela River study found only one bluegill. Today, the river holds 76 species of fish. • The current nest site is the eagles' second. Last year, during fledging, the previous nest partially collapsed from a smaller nearby tree.
CHOW DOWN: Eagles will mainly eat fish, but will also hunt for food such as rabbits, squirrels, snakes, frogs and other small creatures. Eagles are also excellent scavengers, eating any dead animal they can find. • Because much of their diet consists of fish, bald eagles are strong swimmers. In flight, they can lift as much as 4 pounds.
NESTS: Nests are refurbished each spring before the eggs are laid, but other material may be added after eggs are laid and even when the chicks are still in the nest. Nests therefore grow through the years. Most nests are about four feet wide and three feet or more deep. • Nests can get so large that they often bring down the tree they are built in -- a record nest made it to twelve feet wide and fifteen feet tall and weighed over 2000 pounds! • Unlikely many birds, eagle's nests are often flat at the top – not containing the typical "cup" shape.
EGGS: Bald eagles lay white, oval-shaped eggs weighing approximately 125 grams or 4.4 ounces, and are on average about 2.9 inches long and 2.2 inches wide -- just a tad smaller than a tennis ball. • Eagles will typically incubate eggs about 35 days after each egg has been laid. Eggs may be laid two days or more apart, resulting in one chick being the dominant chick of the hatch. KEEPING WARM: Research has shown that eggs are kept at a mean temperature of 101 degrees. The adult eagles turn their eggs regularly, which helps keep all the eggs at the same, even temperature. • The female typically does the majority of incubation, though the male also spends time incubating (some pairs equally share incubation). • Both birds develop brood patches (a bare part of the chest which makes contact with the eggs), but the female typically has a more extensive brood patch. Interestingly, some eagles do not develop a brood patch at all.
GROWING UP: Eaglets will be in the nest for several weeks after they are born. • Eaglets will grow rapidly over a short amount of time and soon be the same size as the parents. They will leave the nest typically during mid-summer and return to the nest until they finally are forced to move away from their parents. • Bald eagles become mature in four years.
WHERE'S THE OTHER ONE? When watching the eagle cam, you may notice only one eagle at the nest. This is very common. The other eagle is likely hunting for food, resting nearby, or “stretching its wings”. At night, the bird that is not incubating is probably very nearby. Bald eagles are very protective of their nest, eggs and young. While either bird is capable of defending the nest, the two work cooperatively to ensure success.
WHY ISN'T SOMEONE SITTING ON THE EGGS RIGHT NOW? Everyone knows that eggs shouldn't get too cold, but they also can't get too hot, or the embryos will die. The adults sit on the eggs when they need heat and get off them when they need to be cooled. In particular, eagles in Pennsylvania lay eggs and care for nestlings in late winter and early spring, so their challenges include snow storms, ice, and rain. These things can be frightening to us, but bald eagles have been coping with them for tens of thousands of years. It is okay for the adults to spend some time off their eggs.