Bald Eagles in Northumberland County

Nature Notes for February 22, 2013

What better way to spend Family Day than birding? A friend told us about an adult Bald Eagle that had been seen regularly along the Rice Lake shore west of Roseneath. These huge birds are always a treat to see, so my husband and I went in search of it. Alas, we were unsuccessful in this location.

We decided to check at Hastings where eagles are often seen in winter. When we arrived, a sub-adult was circling over the river west of the dam over the Trent. At this age, Bald Eagles are mostly brown with varying patterns of white on the wing linings, belly and tail. Sometimes in this plumage, they are mistaken for Golden Eagles. The Bald Eagle has a much bigger head than the Golden. The white on an immature Golden is restricted to the base of the tail and and the base of the primaries. The white on a Bald Eagle is much more variable as to amount and location.

On a hike along the Trans-Canada Trail east of Hastings, we found two more, this time adults with complete white head and tail. They don’t attain this plumage until they are at least four years old. One adult was perched in the sun on one of islands in the river. While we were watching, this bird took flight. Later, we saw two adults flying together, in what was probably a mating display.

Bald Eagles primarily eat fish and carrion. They have been known to harass Osprey until they drop their fish, and then swoop in to catch the fish. The smaller Osprey can do little about this. They can hunt and kill water birds, rabbits and other small mammals. My brother-in-law, who lives in New York State, reported this winter of eagles on the Croton River feeding on American Coot that had become marooned in small areas of open water during a sudden freeze-up.

They build massive stick nests. One in Ohio was reported to weigh almost two metric tons. It was used for 34 years until the tree blew down.  In Ontario, eagles usually nest in trees, although where there are no suitable trees, they will nest on cliffs or even on the ground.

Bald Eagles are long lived birds. The longevity record (from the records of the Bird Banding Lab) is 32 years 10 months in the wild  and 36 years in captivity.

Bald Eagles populations declined dramatically in North America in the mid-twentieth century due to pesticides such as DDT. Eagles are at the top of the food chain, so the pesticides are concentrated in these birds. DDT and related chlorinated hydrocarbons alter the birds’ calcium metabolism in a way that results in thin eggshells. These thin-shelled eggs could not support the weight of the incubating birds and these eggs would break.

 Bald Eagles were listed as endangered by the Ontario Ministry of Natural Resources in 1973.       

Since the early 1970s, when DDT was banned in North America, eagles are making a slow recovery. Studies carried out by BirdStudies Canada on nesting eagles in Ontario indicate that, although Bald Eagles are recovering, they don’t seem live as long or raise as many chicks as was the case pre-DDT. This study is ongoing, so in time, it may determine the reasons for this.

At present, OMNR has downgraded the threat to Bald Eagles, although they still remain a species of “Special Concern” in the province.

If you travel to Hastings over the next few weeks, perhaps you will be lucky enough to spot one.