It is autumn and hundreds of gulls are flocking to Active Pass, feeding off the annual flood of plankton. If you stand on the Miners Bay Dock and watch as they twist and turn and plunge into the water, you might notice two bald eagles swooping in amongst them, their seven-foot wingspans black against the sky.
These eagles are often seen in a tall stand of ‘perch trees’ – large Douglas fir at the south end of the bay – scanning the water for fish or carrion or, in this time of year, lifting off in pursuit of a gull.
Bald eagles often perch in close vicinity to their nest (eyrie), and as Pender Island ornithologist Dave Manning has observed, there are several eyries along that stretch of shoreline. Next time you go by on a ferry, keep an eye out and see if you can spot them. According to Manning, if you see a white head on a nest you’re looking at an eagle sitting on eggs, which would certainly be a welcome sight; out of the 25 nests that Manning observed on Pender this year, only one chick fledged successfully. “Some [of the eagles] didn’t even lay eggs,” he said. “They usually do every single year.”
This decrease was unanimous across the Lower Mainland up to Hope, where only a 20% success rate of nests was recorded. There is no data for Mayne Island fledgling success, but in Active Pass this year, the spotty brown feathers of a young eagle are not present.
The reason for this lack of reproduction is currently unknown, but there are a few possibilities that Manning lists off the top of his head: lack of fish (bald eagle’s number one food source on the coast), human development, climate change, and a decrease in Wildlife Trees.
Eagles are very particular about where they build their nests. On the Southern Gulf Islands, eyries are always within 200 metres of the shoreline and almost always in large Douglas firs with good visibility of the surrounding area. These ‘Wildlife Trees‘ need to be easily accessible in different wind directions and have branches suitable to support nests 2m wide by 1m deep. If nesting eagles make the wrong judgement on this, their eyrie won’t endure throughout the winter storms.
A tree with a nest already built on it is protected by provincial law and cannot be felled or tampered with, however, a concerted effort is also needed to preserve trees with nesting or perching potential. It takes years for a tree to grow large enough to support an eyrie or tall enough to survey from, and with the removal of old growth trees and an increase in urban development, these are becoming few and far between. A fruitless search for nesting trees could interrupt bald eagle breeding periods.
“Trees are going to be a major problem for eagles in the future,” Dave Manning states. “If an eagle can’t find a tree to build a nest in, they’ll leave.”
Do Not Disturb
Even if a pair of eagles do find a suitable nesting tree, there are other factors threatening their productivity. Eagles court, build nests, mate, lay eggs, and raise chicks between February and August, and all within an approximately 3 acre territory. If you are within 100 metres of an eagle’s nest, try your best to reduce development and noise disturbance during this time. Activities like tree removal, blasting, bulldozing, road building and operating heavier machinery can be very distressing to an eagle pair and delay or halt their breeding. If you fly a drone, private helicopter, or plane, your flight path should not be close to nesting eagles. Manning cites a situation on Pender Island where a helicopter began flying overtop two nesting sites a few years ago – neither site has produced fledglings since.
Because raptors utilize large areas for hunting, eat a variety of prey, and are at the top of their food chain, they are excellent indicators of environmental health in their ecosystems.
Toxins bioaccumulate in the food chain and ultimately cause negative effects in birds of prey such as bald eagles, osprey and owls. Humans can help minimize these effects by not using pesticides such as rodenticides or other chemicals. When rat poison is used to control an infestation for example, owls that eat those rats become unintended casualties, which, ironically enough, contributes to an increase in rodent population.
In the 1960s, an insecticide known as DDT drove bald eagles close to extinction in the United States. Used in agriculture, DDT washed into waterways, accumulated in raptor prey such as fish and waterfowl, and affected raptors through thinning of their eggshells, which then broke or didn’t hatch. DDT was banned in 1972 and bald eagle populations recovered and were taken off the endangered list in 2007. This is a great example of how reducing toxins in the environment can make a notable difference for these species, and in fact, make a positive difference for the entire ecosystem. Humans are also susceptible to bioaccumulation, so the less chemicals in the environment the better for everyone.
The Understory and the Wetland
Deer browsing on the islands continues to affect raptor prey populations such as songbirds, amphibians and rodents who live in the declining understory. As Mayne Island residents, where this issue is exacerbated by the invasive fallow deer species, it is important to do our best to rehabilitate and protect the understory on private and public property. Deer fencing and planting of native shrubs can help mitigate this issue, as well as advocating to our government representatives for immediate action on the deer overpopulation issue.
Wetland habitats are important areas to conserve for raptor health as well, as wetlands are critical hunting grounds for bald eagles and other birds of prey. After decades of development on Mayne Island, 90% of the wetland habitats are actually human-made ponds on private property. If your property includes a pond or wetland area, schedule a consultation with Conservancy biologist Rob Underhill to learn how to enhance it for amphibians and other wetland species.
Manning recorded Mayne Island locations of osprey, hawk and eagle nests through the Wildlife Tree Stewardship Atlas, which ran until funding tapered off in 2015. Manning has been busy this year observing nests on North and South Pender for the Islands Trust, but there is no funding for an official, expansive project in any of the Southern Gulf Islands.
With enough effort and action to care for the raptors who share our home, we can make a positive difference and ensure their success and survival. Perhaps next autumn when the gulls congregate once again, the eagles of Active Pass will proudly be joined by their fledglings in the thrill of the hunt.
Maureen Pearl · November 3, 2022 at 8:17 pm
So much enjoyed this months Oystercatcher. Very interesting. Thank you.