Increased tropical cyclones due to global warming could lead to dramatic declines in seabird populations, according to a new study.
Scientists found that after Cyclone Ilsa – a category-5 tropical cyclone – Hit Bedout Island in Western Australia in April 2023, several seabird populations experienced an 80-90% collapse due to the storm at the internationally important breeding site.
The study – published in the journal Communications Earth & Environment – found this level of loss could be unsustainable for seabird populations as the frequency and intensity of cyclones increases due to global warming, with the extreme winds, heavy rain and large swells disrupt their breeding cycles.
Seabirds are crucial to the maintenance of tropical reefs, and the scientists warn that the loss of birds could put further pressure on ecosystems.
The study’s lead author, Dr Jennifer Lavers, a researcher at the Natural History Museum, said: “While Bedout may be one small island in a remote area of Australia, there is so much we can learn from what happened here.
“More than 20,000 animals were lost in the blink of an eye,” she said. “Surveys of the island over three months make it clear that recovery will be slow and likely to be interrupted by another cyclone event.”
Researchers used aerial and ground surveys to estimate the mortality of three species – the brown boobie (Sula leucogaster), the lesser frigatebird (Frigate Ariel), and an endemic subspecies of the masked boobie (Sula dactylatra bedouti) – in the months after the storm.
At least 20,000 birds were lost on the 17-hectare (42-acre) Bedout Island, which mostly breeds adults. The Bedout masked boobie is not found anywhere else. Lavers said Bedout’s example had broader implications for seabirds around the world.
Although it is normal for tropical cyclones to have dramatic impacts on wildlife populations, including seabirds, they are projected to more frequently and violently in a warming world, disrupting seabird populations’ ability to recover.
“The deaths we’ve seen are unprecedented,” said Dr Alex Bond, the chief curator of birds at the Natural History Museum. “The cyclone hit in April, which is quite a peak time when many seabirds were nesting.
“We were able to count the bodies and we estimated that basically all the brown boobies and practically all the masked boobies were killed by Cyclone Ilsa.”
Winds of at least 135mph (217km/h) were recorded in the storm before it made landfall on Western Australia and Bedout Island.
Bond said: “The important thing to remember is that these birds evolved in areas with cyclones. That is not the issue here.
“The problem is twofold: number one was just the intensity of the storm. It was the strongest cyclone to hit Australia, and we are going to see more of it as one of the consequences of the global climate collapse. The other issue is the recovery time.”
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