by Donna Hill B.Sc. B.Ed. 2000
The Bald Eagle is a magestic bird of prey that breeds and winters in British Columbia. This year, the number of wintering eagles counted at Brackendale Eagle Reserve near Squamish, BC is the world's highest at over 3700 birds. Until then, the Chilkoot River in Alaska held the world record at 3500.
Each winter near Harrison Lake, between 500 to 1100 eagles winter on the Harrison Lake and Chehalis River, arriving in Mid-November and leaving by late Feb. The Boundary Bay is another great place to watch them- about 200 spend the winter in the area.
Biologists believe their is an exchange between the populations of these birds, but no conclusive studies have been done yet. They have also recently found pesticide residues in liver samples taken a few years ago in Delta. They believe this is a residue of some pesticides which were used a few years ago to kill wireworm larvae which eat roots of spring crops. This chemical has since been banned.
Bald Eagles are members of the family Accipitridae, which includes Eagles, Hawks, Harriers and Kites. Adult birds get their white head by about 5 years of age. Their eyes and beak change from brown to yellow. Until they make these physical changes, they are often confused for Golden Eagles. They can be told apart by looking for a golden sheen on the head in sunlight (difficult to see) or by looking at the legs. Golden Eagle feathers go right down to the toes where the Bald Eagle feathers stop at the knees. This bare skin allows them to wade in water to scavenge fish-hence their family name of fish eagles. Young bald eagles also have splotches of white on their armpits, young Golden eagles have a white spot on the outer portion of their underwingers and a white band on their tail. Golden Eagles tend to prefer mountainous areas. Bald Eagles are always near water.
Bald Eagles start their migration early-in August. Most birds from Western Canada, Washington and Oregon fly NORTHward to Alaska. Yes, they head NORTH! Why? To feed on the first of the salmon runs. Most Bald Eagles are primarily scavengers and prefer to feed on dead fish. Second choice is live waterfowl, third is mammals. They will also steal food from Osprey.
Once those salmon runs are finished and eaten, they move southward, feeding on each run until it is depleted, moving as far south as Washington, Oregon and Idaho. By February, most coastal dwelling birds head towards their nesting territory. Inland birds wait longer to head to their nests.
Bald Eagle numbers are increasing in British Columbia after many years of decline in North America generally. The first major impact on them, as many other raptors, was use of DDT in the 1960's. This chemical was passed up the food chain and concentrated in predators at the top. DDT accumulates in the fat tissues and cannot be passed from the body. This caused the eagle to lay thin egg shells that were crushed when parents attempted to incubate. It has never been on the endangered list in any Canadian province.
In the Greater Vancouver and Fraser Valley, areas, Bald Eagle numbers are limited by to lack of habitat-huge trees near water due to clearing of forests and development. Many adults are of breeding age, but do not breed.
Nests are placed in large cottonwood or douglas fir trees within 400 meters of water and are used over and over again. These trees must be large enough to hold the 2 tons weight (the size of a VW car) they can grow to over 25 years of use. In the arctic, they nest on cliffs as their are no trees. Nest sites may be protected with a yellow "Wildlife Habitat" sign. This means it is illegal to cut or remove this particular tree. In some areas such as along the coast, a buffer area of several meters is left to protect the habitat around the nest. The BC Ministry of Environment, Fish and Wildlife Dept. maintains a list of nest sites so they can monitor the nests and eagle numbers province-wide.
Two eggs are laid in the south, 3 in the north part of their range. Eggs hatch after 35 days and both parents incubate, then feed the growing chicks. By 8 weeks, they are almost ready to fly and build up their muscles by flapping their wings at the edge of the nest. The young are usually bigger than the adults and lose that weight during the process of learning to hunt for themselves. Young birds head north later than the adults.
Wingspan reaches 2.25 to 2.5 meters (7 to 8 feet) and weight for males is 4.1 Kg (9 pounds) with females reaching 5.5 Kg (12 pounds). Wild adults may reach 25 years of age, more in captivity.
It is best to use a spotting scope to watch these birds as they get disturbed when humans move into their personal space, which varies from 200 to 400 meters, depending on the individual bird. Flying off a roosting perch or feeding area burns energy that they need to survive a long cold winter.