40 year survey sheds light on the future of loon populations in Canada

a adult loon with two loon chicks on its back swimming in a lake Photo by Mark Peck

There may be trouble brewing on the horizon for the common loon (Gavia immer). Birds Canada has released a summary report for its Canadian Lakes Loon Survey (CLLS) program, pulling together all of the data collected by over 4000 volunteer citizen scientists since the program began 40 years ago. The report shows a significant decrease in the number of loon chicks surviving to adulthood, giving researchers advance warning that the future of loon populations in Canada may be at risk. 

The CLLS tracks loon productivity by having volunteers monitor loon breeding pairs and count the number of offspring that survive to six weeks of age. An advantage of counting chicks rather than adults is that the data gives scientists a heads up to how the population may fare in the future. 

adult loon feeding a loon chick in the water
Photo by Mark Peck

“We hardly ever get information with such a high sample size on the number of chicks that a species produces like we get here with the loon survey,” says Doug Tozer, the Director of Waterbirds and Wetlands at Birds Canada. “We’re finding out about this problem with the declining productivity well before we’re going to see reductions in the number of adults.”

The report highlights climate change and its impact on lake chemistry as a possible driver for declining loon productivity. Loon productivity was found to be lower on acidic lakes; for example, CLLS data from acidic lakes in Sudbury, Ontario showed a 6.3 per cent per year decrease in loon productivity over the past forty years, versus Canada’s overall 1.4 per cent per year decline since the early 1990s. Lakes with high acidity are also more likely to have mercury present in the food chain, putting loons at risk of mercury poisoning. And then to add the final blow, rising water temperatures from climate change can also lead to increased mercury in loons. 

This pile-on of environmental effects has been dubbed the “acid-mercury-climate hypothesis.” 

Investigating the acid-mercury-climate hypothesis is a key focus for future research to understand why loon productivity is declining in Canada. Getting to the bottom of it will require researchers to take a close look at the relationship between mercury and loon productivity on the scale of individuals lakes, says Tozer.

“If we’re right, we really need to be more careful with what we pump out into the environment,” says Tozer. “Our industrial emissions over the years have caused problems due to acid rain and mercury contamination, both of which go up into the air in exhaust whenever we burn fuels, and then that pollution is out there, and we can’t get it back.” 

“Then along comes climate change and stirs it all up so-to-speak, and we get ourselves into trouble like may be the case here and now,” adds Tozer.

The report acknowledges that the success of the CLLS program and its findings are thanks to its dedicated volunteers. The program is ongoing, and Tozer says that it works really well as a family-friendly cottage activity. 

Canadian Lakes Loon Survey volunteer monitoring a loon from a kayak
Photo by David Gignac

“You can go for a ride in the boat and check on the local loon pair and see what’s up,” he says. “Include the grandkids and the teenagers if you can. Get them to help fill out the forms, look through the binoculars and count the chicks. I think kids can get really hooked on it.”

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