Even birds living in protected Ontario reserve can’t escape climate change, new study finds

Long Point Bird Observatory is a protected area full of wildlife that is located on a 40-kilometre sandspit — designated a UNESCO Biosphere Reserve — near Lake Erie in southwestern Ontario. It’s also the oldest continuously operating bird sanctuary in North America.

But it appears that climate change is upsetting the natural course of life for its inhabitants.

New research published in the Proceedings of the National Academy of Sciences in the U.S. on June 24 found that tree swallows at Long Point have been producing fewer eggs and are shrinking in body size since researchers started keeping track in 1969.

The research also found that since that time, aerial insectivores, such as tree swallows, have declined by 43 per cent, while the number of insects has dropped by more than 60 per cent since 1977.

The study was carried out by researchers at the University of Michigan and Birds Canada, with historical data from Long Point Bird Observatory.

“Tree swallows are a model organism,” said the study’s lead author, Charlotte Probst, who is a PhD student at the University of Michigan’s School for Environment and Sustainability.

“They’re a species that’s really easy to study because you can just set out these rows and rows of nest boxes — which are essentially like birdhouses in an open field — and the tree swallows are cavity nesters, and so they’ll come to those boxes and breed in them.”

Unlike some other birds, Probst said, tree swallows don’t abandon their nests, which allows researchers to open up the nest boxes and weigh the chicks and count the eggs without being invasive.

A timing mismatch

The study found that insects, including mosquitoes, mayflies and dragonflies, are emerging sooner because climate change is causing warmer temperatures earlier in the year.

But the swallows aren’t keeping up, which creates a disconnect between when the birds migrate and breed, and when the peak availability of food occurs.

Researchers call this a phenological mismatch, one of the major outcomes of climate change.

“Tree swallows used to start laying eggs in approximately the third week of May, and they are now laying eggs in the second week of May,” Probst said. “Peak insect availability also used to be around the third week of May, and now it tends to be in early May or even occasionally late April.”

Matthew Fuirst, a research ecologist at Birds Canada and the study’s co-author, said researchers found that “when there’s years with low insect abundance, which is the food that these aerial insectivores rely on, the birds were of poor condition.”

He found that both the nestlings and adult swallows were smaller in body size when the study ended in 2024 than in previous years. They were also laying fewer eggs in years with lower insect abundance. And this gap appears to be widening.

Thanks to historical data from the observatory, the study found that this mismatch in timing has been increasing by more than three days per decade since 1977.

“All it takes is a tiny skew in timing for it to have a consequence,” Fuirst said.

Declining insect populations play a part

Hadil Elsayed, a PhD candidate at Toronto’s York University who measures insect biomass at Long Point, has also found the temperature is rising faster and that insects are coming out sooner.

Elsayed, who did not work on the study, said the number of “growing degree days” — used to measure heat accumulation and estimate the growth of insects and crops — is similar to the 1990s but occurring two weeks earlier.

This mismatch of insects coming out before the arrival of tree swallows is just one piece of the puzzle, as insect populations are also waning.

“I’m seeing that it’s not really specific to one singular insect group, it’s across the board,” said Elsayed, who is comparing insects at Long Point in the 1990s to the early 2020s.

She measures the biomass through traps that look like tents. They catch flying insects that can then be weighed.

“We’re seeing losses in both terrestrial and aquatic insects, and the variables that seem to be really driving this are changes in vegetation landscape and climate change,” Elsayed said.

What can be done locally?

The University of Michigan’s Probst said although climate change is something the entire global community needs to come together to solve, insect declines are something that can be addressed at a local level in the meantime.

Probst, Fuirst and Elsayed all recommend planting native wildflowers and reducing pesticide and herbicide use so that vegetation can grow and harmful chemicals don’t leach into the environment.

Not removing wood and leaves can also help create habitat for insects, which in turn helps the birds.

“Everything is connected,” Elsayed said. “One change in a specific group really does impact the rest of the food chain.”