Thursday, November 26, 2020

Magnificent eagles, magnificent comeback

By Larry Cornelis – President, Sydenham Field Naturalists

People are in awe of seeing a Bald Eagle.

This is our largest raptor, having a wingspan of 75 – 85” and weighing in at 10 – 15 pounds.

Submitted photo

Females are generally larger than males and northern eagles are larger than eagles from the south (Florida).

Their distinctive dark brown/blackish body with white head and tail is easily recognizable.

They are not bald though.

They are long-lived birds living up to 25 years in the wild (although many perish as adolescents) and up to 50 years in captivity.

They prefer to feed on fish but will eat other creatures and scavenge or steal food.

I saw two on Kimball Road this week feeding on a roadkill raccoon.

A few hours later there was one flying near Reid Conservation Area.

Seeing three eagles in one day without trying to find them is becoming a common occurrence.

But just a few decades ago they were rare and seeing one was a great surprise.

In a sense, eagles (and other raptors) were our canary in the coal mine.

Bald eagle populations plummeted to approximately 1,000 individuals in all the lower 48 states in the 1950s.

It is estimated that in the 18th century, there were from 300,000 to 500,000 bald eagles in North America.

Research found that the use of the pesticide DDT was the cause of the decline.

Because of the affects of DDT, eagles were unable to metabolize calcium properly and the eggshells were thin and weak and broke under the weight of the adult birds incubating the eggs.

So, there was no successful breeding and after a couple decades we almost lost the species (along with other raptors).

Thankfully, DDT was banned, and all raptors slowly recovered.

Today there are approximately 150,000 bald eagles in North America.

Locally, we can see a bald eagle on almost any day.

I have seen 30+ in one day along the St. Clair River in early February.

Bald eagles congregate on the St. Clair and Detroit Rivers, when the great lakes partially (or totally) freeze over, taking advantage of these rivers fast flowing open waters.

Christmas bird counts 30 or 40 years ago may not have tallied a bald eagle but today counts often have 20 or more.

One recent count south of Detroit reported over 200 bald eagles.

Submitted photo

There are numerous nests locally, including in Pinery and Rondeau Provincial Parks, along the Lake Erie shoreline, and in the Sydenham, Thames, Ausable and Grand River valleys.

Bald eagles usually nest near rivers and lakes in large, tall trees.

The nest locations are kept hush as the adults do not like human disturbance or harassment and may abandon the nest if disturbed.

The nests are the largest of any bird species and for that matter, any animal.

The nest can be up to 8’ in diameter and 12’ deep and weigh over a ton.

Typically, two eggs are laid and both adults take turns incubating the eggs for about 35 days.

After hatching, the young take up to 10 weeks to fledge the nest.

Then it takes five years to mature and develop their distinctive white head and tail.

They can be aged by their plumage up to five years old.

People love to see bald eagles and today, thanks to humanity’s efforts, that is easily done.

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