Arden- Arden came to live at the ABEF in May of 2015 from Anchorage, Alaska. While her exact age is unknown, she is estimated to be six years old. Her name is Old English for “eagle valley” or “valley of the eagles”. When Arden first came to live at the ABEF, we thought she was a boy. We quickly realized our mistake when a blood test revealed that she was a girl! Arden enjoys target training, ripping open cardboard boxes, and sunbathing. While Arden enjoys most meals, her favorite days of the week are when she gets to eat salmon or quail.
Bald Eagle Natural History Information
Bald Eagles (Haliaeetus leucocephalus) are the only species of fishing eagle found in North America.
Identification: Bald eagles can be identified by their long wings and relatively large heads. While flying, their wings are often flat, or slightly drooped. Juvenile bald eagles tend to be blackish with white wing pits. As they age, the black begins to turn to brown and the birds appear two-toned. Between their first and sixth years, the birds will continue to molt until they have their full white head and tail and chocolate brown bodies. Juvenile bald eagles and golden eagles (Aquila chrysaetos) may look similar, but there are a few ways to tell them apart in areas where their populations overlap (such as Denali National Park). Juvenile bald eagles lack the golden feathers at the back of the neck that golden eagles are named for. Golden eagles have feathers all the way down to their feet while juvenile bald eagles’ feathers only go about half way down their legs. Finally, juvenile bald eagles tend to have more white and brown speckled plumage while juvenile golden eagles only have white at the base of the tail and underwings.
Hunting & Diet: Bald eagles acquire their food in a variety of ways. Their preferred method is to steal their food from other eagles, ospreys, mergansers, gulls and even river and sea otters. Bald eagles are also well known scavengers and will eat the carcasses of fish, moose, deer, ducks, geese and other small mammals. If a bald eagle cannot acquire food by these methods, they will hunt either by soaring over waterways or by perching in a tree and looking for prey. Although food preference varies by region and season, their primary source of food is fish. In Southeast Alaska, 80-90% of a bald eagle’s diet is fish. One study suggests that bald eagles in Alaska become more active hunters in the winter and half of their diet between November and April consists of waterfowl.
Size: Bald eagle size can vary greatly by region. The largest individuals are in Alaska while the smallest are in Florida. They can stand between 27-35 inches tall and weigh between 4.5-14 pounds with a wingspan varying between 71-89 inches.
Habitat: Because they are a fishing eagle, bald eagles are found along rivers, lakes and, coasts. Any location near a body of water with good foraging habitat is desirable for a bald eagle.
Nesting & breeding: Nest construction/reconstruction and courtship displays usually begin sometime in late March or early April (depending on region it may be earlier). The famous cartwheeling courtship displays can be seen around this time, which usually indicate the couple reuniting after a winter away (or breeding for the first time). The breeding couple builds large stick nests in the tops of trees (preferably old growth) or rocky outcroppings. One study found that 98% of bald eagles nests were within 600 feet of water. Biologists think this is so the parents can easily hunt for fish while staying close to the nest. Typically stick nests are re-used year after year by the same breeding couple and lined with mosses, lichens and grasses. One and three eggs are laid within a few days of each other. Eggs typically have a 36 day incubation period and once they have hatched, the mother does the majority of the feeding. In Alaska, bald eagle nestlings have a 40-50% survival rate. This is due to lack of food, nest predators, or sibilicide where one chick (usually the older one) may kill its nest mates either by physical harm or by depriving it of food. If they survive all of these factors, nestlings usually fledge between mid-August and mid-September.
Other facts: Bald eagles have the ability to soar between 200-300 miles per day, however they often perch in one spot. In Alaska, the bald eagle is the largest raptor, while in the rest of North America, the golden eagle is larger. This size difference is thought to be because of climatic and geographic effects in the state of Alaska as well as the large runs of salmon and other fish in the state. Estimations suggest there are about 100,000 bald eagles in North America with the highest concentration found in Alaska. It is estimated that at the time of fledgling (mid-September) the estimated count for the state is 30,000 individuals. Some of these birds will winter in Southeast Alaska while some individuals have been tracked migrating as far as Central-West Washington.
Most common problems in Alaska: With an increase of development, pesticides/herbicides in Alaska, biologists have seen an increase in the toxicity of fish. Because bald eagles rely so heavily on fish, they are at risk of consuming these deadly toxins that fish may have absorbed. This may not harm bald eagles directly, but it has been linked to their reproductive success. Trauma (collision with powerlines or hit by vehicle), electrocution, emaciation and gunshot accounted for 70% of eagle deaths in Alaska. Lead poisoning has also become a serious problem. It is becoming more common for bald eagles to ingest lead from the tissues of prey that have been shot (such as waterfowl). It is also common for eagles to ingest lead fishing gear picked up by prey items. Lead poisoning is a slow and painful death and we encourage all hunters and fishers to use copper ammunition and sinkers.