Canada jay numbers in southern Ontario decreasing because of climate change, study suggests
Researchers found food supply changes having impact on birds' reproduction
The number of Canada jays in southern Ontario is decreasing because of more frequent freeze-thaw days due to climate change, according to recently published research.
The birds' winter food stock was compromised when fall temperatures fluctuated. The food would defrost, grow bacteria and in some cases become inedible.
And that had an effect on the birds' reproduction and population numbers, University of Guelph researchers found in a study recently published in the scientific journal Global Change Biology.
"If your food is being spoiled, you have less food that you can devote to survival and reproduction," said Alex Sutton, who was a PhD student at the University of Guelph when he co-led the study with Ryan Norris, an associate professor in the university's department of integrative biology.
"What seems to be happening is that they need to decide either to survive or to reproduce," said Sutton, now a post-doctoral fellow at Kansas State University.
If the warming pattern in the fall continues to affect reproduction and food supply, the birds could become locally extinct from Algonquin Provincial Park and other southern Ontario ranges, said Sutton, who is based in Manhattan, Kansas, about 94 kilometres west of the capital Topeka.
Number of nestlings declined
Canada jays are known for storing their food — which can be anything from berries to roadkill meat — in nearby trees for the winter.
However, when their food supply degraded with the freeze-thaw weather, the non-migratory birds produced fewer young or hatchlings in poorer condition, Sutton said.
"On average, the number of nestlings has declined over time, or at least in years where there's unfavourable fall conditions," he said.
And that has long-term implications, according to the study with data spanning almost 40 years.
The study looked at the birds in a small part of the park, about 280 kilometres northeast of Toronto. However, the Canada jay population that has been studied in the park has ranged from a high of 85 to now between 40 and 50 depending on the year, Sutton said.
"Reproduction was really the key thing that was promoting this decline in Algonquin," he said.
The study used bird population numbers from 1980 to 2018, as well as environment data recorded in Algonquin Provincial Park since 1977 to look at the effects of the fluctuations in temperatures on the bird population and their food supply.
Between 1980 and 1996, which had 10 years of above-average freeze-thaw cycles, the researchers found that the birds' numbers dropped significantly.
Although there were fewer above-average number of freeze-thaw cycles and more breeding success in later years, the birds' numbers never rebounded from "a period of poor environmental conditions that occurred several decades prior," according to the study.
David Bird, a retired professor of wildlife biology at Montreal's McGill University, said the amount of detailed data included in the study is impressive but the results are troubling.
"There's still lots of challenges out there," he said. "Climate change is very worrisome."
Birds could go north
Sutton and Bird believe the effects of climate change on the birds' food supply could eventually push the species further north.
The Canada jay can be found in every province and territory, but little is known about the effects of climate change on northern populations.
The study said citizen science databases, like Christmas bird counts, "help to fill this gap in our knowledge and be used to estimate population trends at more northern latitudes." The bird is important to many Canadians, so much so there's a campaign led by Bird and others, like Norris, to name the Canada jay the country's national bird.
Sutton said it's important that we find out more about the Canada jay.
"I think it's really important that we try to understand how this species is actually responding to climate change throughout its entire range," Sutton said.
"This could be a really key point to understanding how future population declines or even changes might occur with changing climate."