The increasingly frequent weather extremes due to climate change include heat waves, which have hit many parts of the world in recent years. Just last summer, the Pacific Northwest and Canada experienced unprecedented high temperatures. Two and a half years earlier, a heat wave hit the Argentine coast. For hundreds of Magellanic penguins (Spheniscus magellanicus) at the large colony near Punta Tombo, temperatures as high as 44 degrees Celsius proved fatal, according to University of Washington researchers in their paper published in early January in the journal Ornithological Applications.
Until 1987, Punta Tombo was considered the largest Magellanic penguin colony in the world, with about 170,000 breeding pairs. Since then, it has shrunk by about 40 percent and currently still consists of around 100,000 breeding pairs. Factors responsible for the decline include food shortages, pollution, and extreme weather events such as the January 2019 heat wave. The heat wave, with temperatures exceeding 40 degrees Celsius in the shade, which killed many penguins, brought the highest temperature ever recorded by scientists in Punta Tombo. Normally, temperatures in the breeding season range from 12 to 38 degrees Celsius. University of Washington (UW) researchers counted 354 dead animals in the days following record temperatures.
“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 doctoral student in biology at the University of Washington. “It’s the first time we’ve recorded a mass mortality event at Punta Tombo connected to extreme temperatures.”
Professor Dee Boersma of the University of Washington began studies at the colony in 1982 and has led the research ever since. She also founded the UW-based Center for Ecosystem Sentinels, which studies Magellanic penguins and other species considered important indicators of ecosystem health.
Of the at least 354 animals that died, nearly three-quarters were adult penguins. Investigations revealed that many of them probably died of dehydration. The researchers found more than a quarter of the carcasses on paths leading from the colony to the sea, where they could have taken up water. Penguins cover their water needs in the sea, with the help of special glands they can excrete the salt. The walk to the ocean can be up to a kilometer, depending on the nest location, and take 40 minutes – apparently too long for many penguins at these temperatures. The researchers often found the dead animals lying on their stomachs with their feet and flippers extended and their beaks open – a common pose for Magellanic penguins to pant and cool.
However, the microclimate of Punta Tombo appears to have played a role in the severity of the impact for the penguins. While about five percent of the adults died in the central part of the colony, there were few or no deaths in other areas. Likewise, access to the sea and individual health and nutritional status may have played a role.
Previous mass mortalities at Punta Tombo observed by UW researchers occurred after heavy rains, with primarily chick deaths. In one year, 50 percent of newly hatched chicks were killed by flooding. However, events such as the 2019 heat wave, which killed large numbers of adult penguins, are of particular concern because the number of reproductive animals is then reduced.
“Any mass die-off like this is a concern”, Holt 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.”
In the colony of Punta Tombo, the sex ratio is clearly shifted towards the males. According to the authors, there are three males for every female, which most likely explains why eight out of ten of the dead adults were male. The gender imbalance has increased over time. As studies by Boersma’s research group show, adult females are less likely to return to Punta Tombo to breed. It is possible that they can no longer find enough food in the open ocean outside of the breeding season – another possible reason for the colony’s decline since the late 1980s.
The 90 chicks that did not survive the 2019 heat wave were well-fed and showed no signs of dehydration. Holt suspects they died because, with their full bellies and small bodies, they couldn’t regulate their body temperatures as well in the extreme heat.
Climate change will lead to more extreme weather events worldwide with severe consequences for people, wildlife, and ecosystems. “Penguins could have the ability to cope, like moving breeding sites”, Holt explains. “But it will take time to investigate whether those adaptations are effective.”
Julia Hager, PolarJournal
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