Bald Eagles in Southern Ontario

Index

The Bald Eagle in
Southern Ontario

The story of Bald Eagles in the lower Great Lakes is a very interesting history. It is a story of overcoming many challenges, such as loss of habitat, contamination of their food and environment, and direct persecution. It is also a story of coming back from the very brink of extirpation in Ontario. Most importantly, the Bald Eagle story is about partnerships; about government and non-government organizations, landowners, and volunteer nest-monitors working together towards a common goal of restoring 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, the Pacific coast, and around large inland water bodies in Saskatchewan, Manitoba, and Ontario. In Ontario, Bald Eagles were once distributed throughout the province, from the lower Great Lakes north to the tree line. Today, Bald Eagles are common only in northern Ontario, and reach their highest nesting densities 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.

In the 1940s through the 1960s, countless tons of an estimated 2,000 chemical compounds were deposited into the Great Lakes, either by direct application or through transportation by air or water. Chemicals that were released into the Great Lakes first entered the aquatic food web by settling into the sediment of lake bottoms. From there, the contaminants spread to the tiny aquatic plants and organisms and then into the bodies of fish and fish-eating birds through a process that is termed "bio-magnification" or "bio-accumulation". Because animals do not excrete toxins, but store them in their tissues, tiny concentrations in the water are bio-magnified up the food chain. Bald Eagles, like humans, are at the top of the food chain. When they consume fish or fish-eating birds such as gulls or ducks, large concentrations of chemicals accumulate in their tissues. This chemical load builds up in their bodies throughout their lives.

This accumulation of chemicals in the eagles’ bodies caused severe eggshell thinning. Eggshells were so thin that the incubating birds often crushed the eggs in the nest. For those eggs that did hatch, the young often had life threatening deformities such as crossed bills. Bald Eagles were not the only species impacted by these toxins in the environment. Other fish-eating birds such as Double-crested Cormorant and Herring Gull also suffered from egg-shell thinning, and other toxic effects.

Although Canada and the United States severely restricted the use of DDT and tightened regulations for disposing of industrial chemicals in the early 1970s, the effects lingered on for many more years. In 1980, the Great Lakes Bald Eagle population experienced complete reproductive failure. There were only three active nests along the north shore of Lake Erie in that year, and no young were produced. The Bald Eagle was declared a provincially Endangered species in Ontario in 1973 and remains listed as such.

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The Bald Eagle in Southern Ontario

The Bald Eagle in
Southern Ontario