History of the Bald Eagle in Southern Ontario

Background

The story of Bald Eagles along the lower Great Lakes includes a history of overcoming many challenges (habitat loss, contamination of their food and environment, and direct persecution) to come back from the very brink of extirpation in southern Ontario. Most importantly, the Bald Eagle story is one of partnerships between government and non-government organizations, landowners, and volunteers working together to restore a healthy population of Bald Eagles to southern Ontario.

Throughout their range, Bald Eagles have undergone dramatic fluctuations over the past two centuries. In Canada, Bald Eagles were once common throughout the Maritime provinces, along the Pacific coast, and around large inland water bodies in Saskatchewan, Manitoba, and Ontario. Whereas Bald Eagles in Ontario were once distributed throughout the province, from the lower Great Lakes north to the tree line, they are currently common only in northern Ontario, with highest nesting densities reached in the northwest. In southern Ontario, Bald Eagles have recovered from near-extirpation in the early 1980s to establish a small, slowly increasing population.

Prior to European settlement, Bald Eagles were abundant along the north shores of Lake Erie and Lake Ontario. An estimated 200 pairs nested from the Ottawa River to the lower Great Lakes, and nesting densities were as high as one nest per mile of shoreline along Lake Erie. Loss of nesting and foraging habitat, through the clearing of land for agriculture, along with direct human persecution, led to a marked decline in the Bald Eagle population in the southern Great Lakes.

Contaminants

The introduction of protective legislation, including the Ontario Ministry of Natural Resources Game and Fish Act in 1890 and the American Bald Eagle Act in 1940, helped the southern Ontario eagle population rebound to approximately 100 pairs by 1950. Unfortunately, this recovery was short-lived due to the introduction of synthetic chlorinated pesticides such as DDT and PCBs into the Great Lakes aquatic food chain.

From the 1940s-1960s, countless tons of an estimated 2000 chemical compounds were deposited into the Great Lakes, either by direct application or through transportation by air or water. These chemicals first entered the aquatic food web by settling into the sediment on lake bottoms, but through a process called bio-magnification or bio-accumulation large concentrations ultimately ended up in the organisms at the top of the aquatic food chain. If an animal cannot break down a chemical, it will build up in their tissues over time. As predators eat large numbers of smaller organisms, which themselves have been storing the toxins they have been eating, large concentrations can build up in those predators at the top of the food chain, such as Bald Eagles. These chemical loads will continue to build up in their bodies throughout their lives, generally with negative results.

This accumulation of chemicals in the eagles bodies caused severe eggshell thinning, which resulted in many eggs being crushed in the nest during incubation. For those eggs that did hatch, the young often had life-threatening deformities such as crossed bills, leading to premature death.

Although Canada and the United States severely restricted the use of DDT and PCBs, and tightened regulations for disposing of industrial chemicals in the early 1970s, the effects lingered on for many more years. The biggest shock came in 1980, when the Great Lakes Bald Eagle population experienced complete reproductive failure. There were only three active nests along the north shore of Lake Erie that year, and no young were produced. Since that time, however, the Bald Eagle population has made a remarkable recovery, with positive, though small, reproductive rates consistently observed. In addition to legislative control of contaminants, habitat conservation and captive breeding programs have assisted in supporting the population.

An indication of the successfulness of recovery efforts for this species came in 2009 when the status of the Bald Eagle in southern Ontario was changed from Endangered to Special Concern. This is a great victory for a bird that was nearly lost from southern Ontario, although monitoring remains an important task to ensure that this positive trend continues.