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Researchers found food supply changes having impact on birds’ reproduction

The number of Canadian jays in southern Ontario is decreasing because of the more frequent freezing and thawing days due to climate change, according to a recently published survey.

The poultry’s winter food supply was depleted when autumn temperatures fluctuated. Food thaws, creates bacteria and, in some cases, becomes unpalatable.

And that had an effect on bird reproduction and population numbers, researchers at the University of Guelph found in a study recently published in the scientific journal Global Change Biology.

“If your food is spoiling, you have less food to dedicate to survival and reproduction,” said Alex Sutton, who was a doctoral student at the University of Guelph when he co-led the study with Ryan Norris, an associate professor in the department of integrative biology of the university.

“What seems to be happening is that they have to decide whether to survive or reproduce,” said Sutton, now a postdoctoral fellow at Kansas State University.

If the warming pattern in the fall continues to affect reproduction and food supply, birds could become locally extinct in Algonquin Provincial Park and other areas in southern Ontario, said Sutton, who lives in Manhattan, Kansas, about 94 kilometers west of the capital Topeka.

Number of nestlings declined

Canada’s jays are known to store their food – which can be anything from wild fruits to dead meat – on nearby trees for the winter.

However, when their food supply deteriorated with freezing and thawing time, non-migratory birds produced fewer young or young in poor conditions, Sutton said.

“On average, the number of pups has decreased over time, or at least in the years when there are unfavorable falling conditions,” he said.

And that has long-term implications, according to the study with data spanning almost 40 years.

The study looked at birds in a small part of the park, about 280 kilometers northeast of Toronto. However, Canada’s jay population that has been studied in the park has ranged from 85 so far between 40 and 50, depending on the year, Sutton said.

“Reproduction was really the key factor that was driving this decline in Algonquin,” he said.

The study used bird population numbers from 1980 to 2018, as well as environmental data recorded at Algonquin Provincial Park since 1977 to observe the effects of temperature fluctuations on the bird population and its food supply.

Between 1980 and 1996, which had 10 years of above-average freeze-thaw cycles, the researchers found that the number of birds dropped significantly.

Although there were fewer above-average freeze-thaw cycles and more reproductive success in later years, the number of birds never recovered from “a period of poor environmental conditions that occurred several decades earlier,” according to the study.

David Bird, a retired professor of wildlife biology at McGill University in Montreal, said the amount of detailed data included in the study is impressive, but the results are worrisome.

“There are still a lot of challenges out there,” he said. “Climate change is very worrying.”

Birds could go north

Sutton and Bird believe that the effects of climate change on the birds’ food supply could push species further north.

The Canadian jay can be found in all provinces and territories, but little is known about the effects of climate change on northern populations.

The study said that citizens’ scientific databases, such as bird counting at Christmas, “help fill this gap in our knowledge and are used to estimate population trends in more northern latitudes.” The bird is important to many Canadians, so much so that there is a campaign led by Bird and others, like Norris, to name Canada’s jay as the country’s national bird.

Sutton said it is important to find out more about Canada jay.

“I think it’s really important that we try to understand how this species is really responding to climate change to its full extent,” said Sutton.

“This can be a really key point in understanding how the future population declines or even changes can occur with climate change.”

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