With heatwaves forecast to become increasingly intense and more frequent due to the continuing rise of anthropogenic greenhouse gas emissions, researchers at the University of Washington have said there will be “far-reaching consequences not just for humans, but for wildlife and ecosystems”.
A research team focussed on the impact of a January 2019 heatwave in Punta Tombo, on Argentina’s southern coast, when temperatures spiked to 44C (111F) in the shade.
The extreme heat wave killed at least 354 penguins in the days following the record high temperature.
“This extreme event fell near the tail end of the breeding season for Magellanic penguins, so it killed a large number of adults, as well as chicks,” said lead author Katie Holt, a UW doctoral student in biology.
“It’s the first time we’ve recorded a mass mortality event at Punta Tombo connected to extreme temperatures.”
The heat wave saw the highest temperature the researchers have ever recorded at Punta Tombo, where UW teams have been studying Magellanic penguins since 1982 under co-author P Dee Boersma, a UW professor of biology.
Temperatures at the site during the breeding season typically rise from around 10C (50F) to 37C (100F).
Researchers had previously only recorded a shade high of 43C once, but that record was not associated with a mass die-off of penguins.
The extreme heat in 2019 affected adults and chicks differently. Nearly three-quarters of the penguins that died – 264 – were adults, many of which likely died of dehydration, based on postmortem analyses conducted by the UW researchers.
They found 27 per cent of adult penguin corpses along paths heading out of the breeding colony to the ocean, where they could get a drink – penguins have glands that can filter salt out of the water.
A journey from the colony to the ocean can stretch up to one kilometre and, at its longest, might take an adult penguin 40 minutes to complete.
The researchers said the dead adult birds were often found on their stomachs with their feet and flippers extended and mouth open, a common panting and cooling pose for Magellanic penguins.
Some sections of Punta Tombo, where thousands of Magellanic penguins gather to breed each austral spring and summer, fared worse than others. In the central section of the colony, about 5 per cent of adults perished.
Research teams at the University of Washington have previously documented mass mortality events at Punta Tombo linked to severe rainstorms that primarily killed chicks, including one year where deluges killed 50 per cent of the colony’s recently-hatched offspring.
But the 2019 heat wave is a particular concern because it led to the loss of a large number of adults in a single event, Ms Holt said.
“Any mass die-off like this is a concern,” she said. “But what is most concerning about heat-death mortality is that it has the potential to kill a lot of adults.
“The population viability of long-lived seabirds like Magellanic penguins relies on long lifespans. Adult Magellanic penguins can live more than 30 years, so they typically have many opportunities to successfully raise chicks. If we’re losing large numbers of adults from a single event like this, that’s a major concern.”
The climate crisis is already causing more extreme weather events globally, though effects will continue to vary by locality. The researchers said the consequences of this heat wave, though grim, also show scientists the limits that some species can endure.
“Penguins could have the ability to cope, like moving breeding sites,” said Ms Holt. “But it will take time to investigate whether those adaptations are effective.”
The research is published in the journal Ornithological Applications.
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