Here’s what’s causing the decline of loon chicks in Ontario

Published: July 7, 2020

loon and chicks Photo by Jim Cumming/Shutterstock

It’s hard to imagine a canoe trip on a Canadian lake being complete without the eerie hoots and yodels of the iconic common loon. Unfortunately, data collected over the last 38 years by over 2,000 volunteers from the Birds Canada citizen science program called the Canadian Lakes Loon Survey has shown that loon reproductive success is on the decline in the province.

Now, researchers from Birds Canada, Acadia University, the Ontario Ministry of the Environment, and Ottawa, have published a study showing that declines of loon chicks are steeper on lakes with higher acidity and mercury levels.

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The findings suggest that changing lake conditions as a result of climate change may be threatening the future of common loon populations in Ontario. Kristin Bianchini, the study’s lead author and a postdoctoral researcher with Acadia University and Birds Canada, says that because loons are top predators on lakes, understanding how chicks are faring can reveal a great deal about the health of Ontario’s watersheds. “The lake where a chick hatches is its only source of food,” she explains. Any changes to the lake environment that upsets the food supply will impact a loon chick’s ability to survive. The researchers found that the decline in the production of common loon chicks was steepest on acidic lakes.

Acidic lakes are a lingering symptom from decades ago when sulphur dioxide emissions in North America caused acid rain. While we’ve reduced our acid emissions, it may take decades for many lakes to recover from the effects of acid rain, suggests Bianchini. And that’s bad news for hungry loon chicks because high acidity can reduce fish numbers.

Loon health is also impacted by the presence of pollutants in lakes. If there are toxins in the water being absorbed by organisms in lower levels of the food chain, those contaminants can end up concentrated in the bodies of top predators like loons.

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Researchers found mercury to be associated with loon chick declines. It is very persistent in the environment, Bianchini says. It can contaminate forest soils and sediments in lakes and wetlands. High precipitation events can also wash mercury-contaminated soils into waterways.

Mercury, a neurotoxin, turns loons into“bad parents”, she says. Affected parents incubate their eggs less and they don’t feed their chicks as often. In order to be absorbed into the bodies of living organisms, mercury must be chemically altered by a process called methylation, says Bianchini. This process is thought to occur more commonly in acidic lakes, and at a faster pace in warm water.

“Take lakes that are still acidic from acid rain a few decades ago, then add a touch of climate change in the form of increasing temperatures and extreme precipitation events, and you get a strong dose of mercury flowing up the food chain and into loons,” she says. “We think this might be a big part in explaining the declining trend in common loon productivity in Ontario.”

One surprising outcome of the research was that the study found no relationship between human disturbance and shoreline development, and loon productivity. “We measure productivity as the number of chicks produced when a nesting attempt was made,” she says.

“One explanation for this finding is that human disturbance and shoreline development are actually so important that when they reach high enough levels, the loons don’t attempt to nest at all.” With no nesting, there is no chance for these factors to influence productivity.

Cottagers can ensure a loon-friendly property by creating shelter for loon chicks, and letting native wetland plants grow along their shoreline. “It’s also really important to be careful while boating,” she says. Driving slowly, especially while approaching the shore, helps to prevent wakes from washing out loon nests and from separating small chicks from their parents.

If you regularly visit a lake in the summer, consider participating in the Canadian Lakes Loon Survey to help researchers keep an eye on this iconic species.

The longest-running citizen science program operated by Birds Canada, the Canadian Lakes Loon Survey, requires participants to spend at least three days visiting a lake: once in June, to see if any loons have paired up; once in July, to see if any chicks have hatched, and once in August, to see if the chicks have survived long enough to fledge.

“This study would not have been possible without the amazing work of these citizen scientists at Birds Canada, and I am hugely grateful to everyone who has participated in the Canadian Lakes Loon Survey,” she points out.

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