In 2019, Emily Choy rappelled off the side of a guano-covered cliff almost 400 feet above Hudson Bay, and reached for a sleek black-and-white seabird. The laughing calls of more than 60,000 thick-billed murres surrounded her.
Choy, a postdoctoral researcher at McGill University, hoped to capture a live murre in order to take it back to a remote field lab and test its tolerance for heat. Researchers from Coats Island, near Nunavut, Canada, had reported finding dead murres still perched atop their nests after warmer temperatures in 2011 and before that, in the late 1990s. A combination of overheating, intense mosquito attacks and the murre’s dedication to protecting its sole egg of the year appeared to be to blame.
But Choy’s research focused on a different potential cause of the birds’ mortality: exceptionally low physiological tolerance for heat. Her research, which found experimental evidence of murres’ susceptibility to heat stress, appeared earlier this month in the Journal of Experimental Biology.
Choy’s study was part of a Canadian-based project called ArcticSCOPE, which is investigating the direct impacts of heat on two Arctic bird species, thick-billed murres and snow buntings, which are songbirds.
Heat stress is an emerging focus of Arctic research. As extreme heat waves become more frequent and rapid warming threatens northern latitudes, the same adaptations that have allowed animals to survive cold temperatures are the ones that may make them more susceptible to heat. Scientists want to know which species will be able to adapt to the hotter conditions of the High North, either through evolution or changed behavior, and which ones won’t.
“This is a big topic in the sciences. Can animals keep pace with climate change?” said Ryan O’Connor, a postdoctoral fellow at the Quebec Center for Biodiversity Science at the University of Quebec at Rimouski, who does research on snow buntings for the ArcticSCOPE project.
For murres and buntings, the answer to this question is tricky. “I mean the buntings can’t go any farther north,” O’Connor said.
Birds aren’t the only animals at risk for heat-related stress and death. Large mammals and cold-blooded species, like fish, may also be at risk, as temperatures rise to levels that exceed their ability to cope with heat. In the 2018 Arctic Report Card, the National Oceanic and Atmospheric Administration identified a more than 50 percent decline in the herd size of caribou, which to manage heat stress, in addition to panting, rely on dwindling patches of snow left over from winter. Scientists are concerned about what the resulting changes in behavior and physiology will mean for the long-term existence of Arctic species and what happens when those shifts interact with other factors, such as habitat loss.
“There has been very little work done on the direct effects of heat on Arctic species,” Choy said. “Our study is the first to look at heat stress in a large Arctic seabird [and shows] it might be a very important but underreported source of stress.”
‘Canaries in the Coal Mine’
Because of murres’ black backs, their body temperature can reach nearly 115 degrees Fahrenheit (46 degrees Celsius) in the sun, even on a 75 degree day. Choy researched how well these seabirds can cool down when temperatures rise.
In short, “very, very poorly,” Choy said. The Arctic, which is warming more than two times as fast as the rest of the world, is an early warning system for the effects of climate change, Choy said. “Arctic birds such as thick-billed murres could be canaries in the coal mine for the effects of climate change.”
Mass die-offs of the common murre, a closely related species, in which tens of thousands of the birds washed up dead on the shores of Alaska and the west coast of North America in 2015 and 2016, were attributed to a marine heat wave in the Pacific Ocean that sent negative effects cascading throughout the food web. Choy said her research differed from that of researchers who studied those mass die-offs. Rather than looking at indirect effects of warming on food supply, she and her collaborators wanted to learn how heat directly impacts the physiology of these birds.
Arctic animals, such as murres and buntings, have high metabolic rates, a great adaptation for generating heat in cold climates, Choy said, “but, of course, that’s a disadvantage when you’re in the heat.”
When birds overheat, they begin to pant to cool down. Yet at some point, their panting becomes insufficient to offset the heat generated by their high metabolic rates. At that point, internal overheating spikes, which can cause reproductive failures or worse.
It would be like working out in the peak of summer while wearing a jacket, O’Connor said. But cold-adapted animals can’t take off their metaphorical jacket of evolution to cool down.
Thick-billed murres have the poorest ability to dissipate heat ever reported in birds, Choy said. “Not only that, they actually became worse at higher temperatures,” she added.
O’Connor has found that snow buntings, songbirds whose summer breeding ground is in the Canadian High Arctic, have, like thick-billed murres, a low capacity for beating the heat. “This animal has become an expert in the cold but at the potential cost of being very poor in the heat,” said O’Connor.
A Likely Decline
Even when murres and buntings survive a heat wave, they’re susceptible to subtler but still detrimental effects of warmer temperatures.
As murres and buntings begin to focus more on cooling down to avoid heat stress, it could come at the cost of neglecting their young, said O’Connor. Murres may make more trips to cool down in the water, leaving their nests open for predation from glaucous gulls and Arctic foxes, as one study found in a different Arctic seabird, the skau. Buntings, on the other hand, may not spend as much time feeding themselves or their hatchlings in the heat, O’Connor said, based on the findings of his study, published earlier this year in the journal Ecology and Evolution. In both species, the trade-off between coping with heat and caring for their young is likely to result in lower survival rates among the birds’ offspring.
“It’s going to be a slow-moving, gradual problem,” O’Connor said. “I would say it’s a pretty strong likelihood that we would see a population decline in buntings in the future if the Arctic continues to warm at the rate that it’s warming.”
Though the thick-billed murre population on Coats Island is currently stable, Choy said, warmer temperatures in the future could push the birds—an important food source for Inuit communities in Greenland and off the coast of Newfoundland—over the edge.
While other animals like Atlantic cod and herring are extending their ranges northward to escape the warmer waters, murres are extremely loyal to their breeding sites, even nesting in the same area of their home cliff decade after decade. Choy said neither she nor other scientists have found evidence of murres moving farther north to breed and it’s unlikely they will in the future.
O’Connor said it’s unlikely that buntings and murres could evolve to adapt to warmer temperatures. “It’s not like an insect that just reproduces in millions. [These birds] have a slow reproductive cycle and therefore slow adaptive rate,” he said. “It’s tough to match the rate of climate change.”
Locally Adapted or Locally Extinct?
While snow buntings and murres might be some of the most poorly adapted birds at coping with heat, they are not the only animals of concern. Heidi Golden, research associate at the University of Connecticut and science consultant at Golden Ecology LLC, studies the role that warmer temperatures in Alaska and Canada might have on the future of the Arctic grayling. The fish is an important food source for local residents, including Alaska Natives and First Nations people in Canada.
Arctic grayling could be another “canary in the coal mine” for how animals will fare in a hotter world, Golden said.
Her findings have connected differences in the heat responses of two distinct populations of grayling—one adapted to warmer streams, the other to colder water—to differences in their genome.
She and her collaborators, Mark Urban and Jill Wegrzyn, at the University of Connecticut, and Linda Deegan, at Woodwell Climate Research Center, found that graylings that live in slightly colder streams may be less likely to survive in a warmer world. As in the murres and snow buntings, Golden said, this is due to a “ramped up” and overstressed metabolic response. Preliminary data suggests it’s correlated with differences in regions of the genome that code for heat shock proteins and other traits related to metabolism and stress, Golden added.
“Some populations are locally adapted to warmer temperatures and what we would expect is that those populations will probably be the ones that will survive in climate change conditions,” she said.
Golden said changes in habitat driven either by precipitation or human activities also threaten Arctic graylings. If cold-adapted populations go locally extinct in certain streams, she said, warm-adapted fish could repopulate those areas.
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The ability of grayling populations to move through and across watersheds, she said, is also decreasing as humans expand infrastructure in their habitat. “The First Nations in Canada are losing their Arctic grayling populations,” Golden said. “Part of that is due to roads that have poor culverts. The fish can’t get into habitat where they would normally go to spawn.”
But Choy said that despite the threats to Arctic animals, she does not believe their survival is hopeless.
“With climate change it’s the impact of multiple stressors that hurt species,” she said. “If we can understand what some of the stressors are, like temperature, maybe there are others, such as [habitat disturbance] that we can control.”