02. Chickadee Notes

Bald Eagle in New Brunswick

EagleGenerally, Bald Eagle, Haliaeetus leucocephalus, populations in Canada have not shown the marked declines that have been observed at their scattered breeding locations in the lower 48 states of the United States. Although the Bald Eagle is still a fairly common nesting bird in western Canada and Alaska, it has never bred commonly in New Brunswick. Since 1976 the Bald Eagle has been protected in New Brunswick under the provincial Endangered Species Act. It is very encouraging that over the last two decades numbers of eagles nesting annually in New Brunswick have increased from about 15 nesting pairs to more than 30. Most of the breeding population is found in the southwest, where nesting occurs near freshwater lakes, rivers, estuaries, and on marine islands. Historical records suggest that there are now fewer Bald Eagles nesting in northern New Brunswick, including the large Miramichi drainage, than in the past. Since 1950 there has also been a decline in the numbers of immature Bald Eagles summering in New Brunswick. Prior to 1950, it was estimated that at least 100 eagles summered in the lower Saint John River basin. At that time the area was considered one of the most important summer habitats for this bird in the northeast maritime region of the continent. As many as 18 birds could be observed in the air at one time at French Lake, York County, and it was not uncommon to see 20 to 30 eagles in a day on the extensive wetlands of central New Brunswick. Surveys in the mid- 1970s revealed but a single pair in the region. Earlier banding studies had shown that some of the immature Bald Eagles that summer in New Brunswick were fledged from nests in the southeastern United States, where frequent nest failures had been reported for several decades.

Natural History

The Bald Eagle is Canada's largest bird. An adult may have a wingspan in excess of 2 m and may weigh more than 7 kg. Adult birds are unmistakable, with their dark brown plumage and striking white head and tail. Juvenile Bald Eagles are entirely brown, although frequently mottled with white on the belly, back or tail. Only when they reach maturity at the age of four or five years do they acquire the distinctive white head and tail and vivid yellow feet and bill. Toes are equipped with strong, sharp talons, ideally suited for grasping prey.

Scavenging and stealing prey from other predators play an important role in the hunting strategy of the Bald Eagle.

Although eagles hunt most commonly from perches close to water, they will also hunt on the wing and even on the ground. Not surprisingly, fish are the staple of the Bald Eagle diet, but aquatic birds and moderate sized mammals are also important. Scavenging and stealing prey from other predators are important in the hunting strategy of the Bald Eagle, particularly among juvenile birds. It is not unusual for startled duck hunters to watch their fresh kill disappear in the talons of a Bald Eagle before it can be retrieved from the water.

The Bald Eagle is noted for a spectacular courtship ritual, a portion of which includes a manoeuvre known as the "cartwheel display". The behaviour involves the male and female swooping alternately at each other, while carefully avoiding contact through side slips and steep, rapid climbs into the air. Turning on its back, one bird will grasp the outstretched talons of its oncoming potential mate. The pair then tumble earthwards in a spinning cartwheel, releasing their hold on each other only metres above the surface.

The species favours areas where fish are plentiful...

No other North American bird constructs a nest as large as that of the Bald Eagle. Nests average l.5 to 2 m across and 1 m in height. Bald Eagles may return to the same nest year after year, adding new material and rearranging old. The result can be an enormous nest. One such older nest measured 3 m across and was 6 m high. Nests are constructed of tremendous masses of sticks, with nest cups lined with grasses and various small plants. Nest building is largely the work of the female, although the male will assist when materials are first brought to the nest.

Clutches usually include two large, dull white eggs, although on occasion there may be as many as three. Both male and female share incubation duties. The eggs hatch two or three days apart after being incubated for about 35 days. The hatchlings, covered with a gray down, receive constant attention from both parents for the first three to four weeks of their life. The largest eaglet is the first to receive food and will on occasion kill a smaller sibling. It is about six or seven weeks before the young eaglets are able to feed themselves. After 10 or 11 weeks gray down has been replaced by flight feathers. At this stage the eaglets begin to make short excursions, hopping up and down and flapping to perches around and above the nest. First flight occurs after about 78 days. Although the eaglets then leave the nest they will return to roost and feed there for the next couple of months. The early years present many hazards and in some populations less than half of all young produced may reach adulthood. In New Brunswick, Bald Eagles breed in April and May. At this time the male and female defend a 1 to 2 km2 nesting territory against other eagles. The species favours areas where fish are plentiful and shorelines are lengthy. In this respect New Brunswick coastal areas and larger inland lakes are ideal.

Bald Eagles prefer to build their nests in tall trees that provide an unobstructed view, as well as easy access. When trees are scarce or absent, Bald Eagles will build their nests on cliff ledges or even on the ground, although in New Brunswick trees are the only nest sites that have been recorded.

Bald Eagles are not territorial on their winter ranges, where they may roost and feed communally, sometimes in large numbers. They winter regularly along the Bay of Fundy coastline, particularly among the islands of Passamaquoddy Bay and the lower St. John River. Winter weather, ice conditions and food availability all affect the movements of these birds.

... more than half of all reported Bald Eagle deaths are due to shooting and incidental trapping.

Bald Eagles first experienced a significant decline in numbers in the late 1880s, primarily in the United States. Like many predators, they were considered a threat to human interests and were trapped and shot at every opportunity. Although attitudes generally have since changed, even today more than half of all reported Bald Eagle deaths are due to shooting and incidental trapping. The first conviction under the New Brunswick Endangered Species Act occurred in 1985 when two men were fined for shooting and clubbing a juvenile Bald Eagle to death.

The introduction of the pesticide DDT in the late 1940s led to a further decline in some populations of Bald Eagle. As with other predatory birds, DDT became concentrated in the tissues of adults, with disastrous consequences. Females produced thin-shelled eggs that broke or were crushed before they could hatch. The use of DDT and related compounds has now been discontinued in North America, with the result that eagles are now nesting more successfully.

Helping Out

Canadian Bald Eagle populations are generally stable or increasing slightly. In New Brunswick this magnificent bird is doing well, but is not out of danger. The New Brunswick Department of Natural Resources and Energy surveys and monitors eagle nests in the province each year. We can all help by ensuring that nesting birds are not disturbed, and that trees used for nesting or regular perching are not cut down. The acidification of lakes can reduce the quality and number of fish available for eagles. It is important that we urge politicians to press for international co-operation and tougher legislation to control air contaminants which lead to acid rain. Bald Eagles can be poisoned by lead ingested with waterfowl that have been pirated or scavenged. If you are a duck hunter ensure that all birds are retrieved.

Further Reading

Bent, A.C., 1937. Life histories of North American birds of prey. Part 1. Reprinted in 1961 by Dover Press, New York. 409 pp.

Brownell, V. R. and M.J. Oldham, 1984, 1990. Status report on the Bald Eagle, Haliaeetus leucocephalus in Canada. Committee on the Status of Endangered Wildlife in Canada, Ottawa. 45 pp.

Erskine, A. J., 1992. Atlas of breeding birds of the Maritime Provinces. Nimbus Publishing Ltd. and the Nova Scotia Museum. 270 pp.

Gerrard, J. M. and G.R. Bortolotti, 1988. The Bald Eagle. Western Producer Praire Books, Saskatoon. 177 pp.

Stocek, R. F., 1979. Decline of summering Bald Eagles in central New Brunswick. Canadian Field-Naturalist. 93: 443-445.

Stocek, R. F. and P.A. Pearce, 1981. Status and breeding success of New Brunswick Bald Eagles. Canadian Field-Naturalist 95: 428-433.