Technology & Science

Bald eagles soar back, but return may be fragile

Bald eagles have made a comeback in southern Ontario over the last decade after dying out because of the pesticide DDT, but the magnificent birds are not out of the woods when it comes to long-term survival.

Birds are breeding in southern Ontario, but their health depends on clean water and food

A bald eagle soars along the Squamish River in Brackendale, B.C. The bald eagle disappeared from southern Ontario in the 1980s, but now there are close to 100 nesting pairs. (Richard Lam/Canadian Press)

Bald eagles have made a comeback in southern Ontario over the last decade after dying out because of the pesticide DDT, but the magnificent birds are not out of the woods when it comes to long-term survival.

After years of effort to bring the birds back, there were 71 nesting pairs of bald eagles in southern Ontario in 2011, the last year they were intensively monitored.

There may be close to 100 nesting pairs now, says Jody Allair, a biologist with Bird Studies Canada who keeps an eye on bald eagle populations with the help of volunteer sights.

Bald eagles have been seen from Ottawa to Kingston to the Bruce Peninsula and along the shores of both Lake Ontario and Lake Erie.

If 200 eagles doesn't sound like many birds, it isn't. Although these birds are now reproducing, they are still susceptible to chemicals in the environment and the health of both the tree canopy and Ontario water systems.

"We don't want to take our eye off the ball with the bald eagle. We're no longer intensively monitoring eagles, but if we see anything wrong, we have to act because it could go bad in a hurry," Allair told CBC News.

The Ontario Ministry of Natural Resources, Canadian Wildlife Service and Bird Studies Canada monitored the birds intensively from 2004 to 2012.

Recovering across Canada

Bald eagles have become numerous and very visible inhabitants of the B.C. Lower Mainland. In Ontario, they've gone from threatened species to a species of "special concern."

Their numbers are now so numerous in Atlantic Canada that they're being sent to the U.S. to try to help along the recovery of their bald eagle populations.
Bald eagles like to nest by water, but that makes them to susceptible to any pollution in water systems. (Submitted by June Ryan )

But tests in southern Ontario show high concentrations of mercury, PCBs and flame retardant in the flesh of eagles.

"Blood and tissues test positive for flame retardant chemicals. There is also high quantities of lead in the birds. It only takes one lead shot to poison water," Allair says.

The Canadian Wildlife Health Co-operative, a research group that looks at the health of animal populations, found in 2015 that poisoning from insecticides or lead was the most common cause of death of eagles in the Prairie provinces. Lead shot is still used in hunting and eagles are scavengers.

Susceptible to chemical contaminants

Because they are the top predators in their ecosystem, bald eagles get a concentration of the chemicals absorbed in various ways by animals further down the food chain, mainly fish and waterfowl, their favourite food.

They like to nest by water — most are within one kilometre of a lake or river — so their health is dependent on clean and viable aquatic systems, Allair says.

While bald eagles have shown tolerance for city living in Vancouver, where they have access to the ocean, they generally avoid habitats with much human activity.

What they really like is a good strong high tree that can support their nests, which can weigh as much as a small car, says Allair.

In southern Ontario, they like cottonwoods or sycamore; in the north, white or red pine. One limiting factor in their recovery might be the health of southern Ontario's forest cover, which has been affected by climate change, as well as habitat destruction.

Legacy of DDT

The recovery of the bald eagle in southern Canada is a "good news story," Allair says.

But he worries that the story of how they were wiped out is being lost.

In 1980 there were only three nesting pairs in southern Ontario and no babies were born after DDT made their eggs too thin for them to survive. Then all the adults died.

"It took a lot of political pressure to get DDT banned," Allair says.

Bringing back the bald eagle involved years of intensive management, including building nesting platforms, working with landowners, cleaning up wetlands and bringing in eagles from elsewhere to boost the genetic diversity.

"The story is getting lost, people are forgetting how much damage we've done," Allair says.

Allair loves watching bald eagles, who mate for life and co-operate with their mate in building the nest and raising young — usually just one per season.

"I do love them. They're wonderful birds, very intrepid," he says.