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Bald eagles in Nova Scotia may be disrupting other bird populations

  • Mar 04, 2014
  • 613 words
  • 3 minutes
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A local birdwatcher believes a local farm’s practice of feeding chicken to bald eagles in Nova Scotia’s Annapolis Valley is causing a major disruption to avian ecology.

But without any kind of study being funded on bird populations, it’s difficult to be certain what’s happening.

Blake Mayfield, a member of the Nova Scotia Bird Society and a local avian expert, says winter is usually a tough time for eagles. But a sizeable gang are sticking around an area they didn’t always inhabit in Annapolis Valley.

“They’re smart birds — they figured out pickings are pretty good.”

Mayfield says this is good as it suggests eagle populations are recovering from the low numbers experienced in the latter part of the 1900s. But he believes that as the eagles make a comeback, other birds in the area are being negatively affected.

While the baldies don’t prey on birds like osprey directly, the large raptors could be bullying them out of their nests, resulting in the osprey’s reduced population. He also has a theory that avian populations nearby on the Bird Islands are being affected by gangs of bald eagles that prey on the young of great cormorants and several species of gulls.

He says that making a habit of feeding the birds could create a larger ecological problem.

However, some bird experts don’t agree that eagles are the root cause of avian population disturbances in the area, pointing to other things like climate change and broader regional ecological variation.

Michel Gosselin, an ornithologist at the Museum of Nature, says it’s too localized to tell whether the farm is having a larger effect on avian ecology. “These species have lived alongside each other for thousands and thousands of years,” he says.
But he concedes that the eagles may be causing a problem by hanging around uncharacteristic habitats due to the introduction of an artificial food source.

“Normally there’s a balance between the predators and the prey,” he says. But if for some reason the predators are fed artificially, he says their numbers will increase and disrupt birds lower on the food chain.

He says that nonetheless, it would be a localized problem that may be part of a bigger equation that includes climate change or the human disruption of habitat in general. The big change wasn’t feeding chicken to the eagles so much as building the chicken farm in the first place. “It’s only the drop in the bucket in an ocean of changes of what we do to the environment,” he says.

But it could also have to do with larger ecological patterns. “The ecology of a backyard is not the same as the ecology in the boreal forest,” Gosselin says, pointing to the example of northern birds like the pine grosbeak not making as many appearances in Ontario or Quebec this year because evergreens and spruce have produced a good crop of cones for them to feed on farther north.

“If you want to see why (the range of) eagles and cormorants are changing, it’s obviously not because of a single chicken farm,” he says.

Ian McLaren, a retired professor emeritus from Dalhousie University who researches birds, agrees. “On the face of it, there doesn’t seem to be an issue (with the chicken farm).” He points to things like the change in sea acidity or salinity as possibly affecting avian populations on the Bird Islands.

Nonetheless, Gosselin says there could be a problem if chicken farms are feeding eagles all over, and everyone agrees that more scientific attention needs to be focused on the situation.

“I think there’s a good argument to be made to launch a large scale bird project,” McLaren says.


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