By Jon McCracken, Long Point Bird Observatory

At the turn of the century, Bald Eagles were common along the shore of the Great Lakes, including Long Point. Beginning in the late 1940's, however, along came the introduction of some really nasty and very persistent insecticides like DDT, into the aquatic food chain. Because the toxins are not excreted by animals, but rather stored in tissue, tiny concentrations of toxin in the water are "bio-magnified up the food chain. Eagles are at the top of the food chain, so they accumulate large amounts of the toxins. A couple of decades later, biologists were puzzled by alarming declines in the populations of eagles and other birds of prey. The birds were disappearing from the lower Great Lakes region in particular; and eagles had all but disappeared from Long Point It was discovered that the declines were mostly due to extremely poor reproductive success brought about by the toxins, which thinned the eggshells to the point where the incubating birds crushed the eggs in the nest. For those eggs that did hatch, the young often showed life threatening external deformities. If the toxins were having this kind of major impact on birds, what effects might they have on people'? Prompted by both environmental and health concerns, the pesticides were ultimately banned in both Canada and the U.S. (they are still widely used in Latin America). Before long, scientists reported that levels of the banned substances were slowly declining in the food chain. In fact, the tremendous flow out of the Great Lakes was flushing them out of the system faster than had been previously predicted. With this knowledge, hopeful biologists working for the Ontario Ministry of Natural Resources and the Canadian Wildlife Service began a program to release young Bald Eagles at Long Point over the course of several years in the 1980s. Combined with falling pesticide levels, the release program appears to have been a success. Though still not a common sight, up to 5 pairs of eagles now nest in the Long Point region. In a cooperative program with the Ontario Ministry of Natural Resources and the Canadian Wildlife Service, Long Point Bird Observatory biologists are monitoring the Long Point population of eagles, and indeed all of the eagle nests in southwestern Ontario. Each summer, all young are banded with special coloured bands, and blood and feather samples are taken to monitor contaminant exposure. Contaminant levels have come down a lot over the last few decades. However, the birds are still picking up some toxins locally, and even more on their wintering grounds. Reproduction, though still not great, is nevertheless improving all the time. The Bald Eagle is still considered endangered in Ontario, but its future is a lot rosier now than it was just a decade ago.

Bald Eagle Monitoring in Southern Ontario

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