Intensifying Tropical Storms Threaten Seabirds, New Research Shows

More intense and frequent tropical cyclones and hurricanes are threatening some seabird populations more than previously thought, scientists said this week as they released a new study showing how a 2023 tropical cyclone wiped out 80 to 90 percent of the populations of three species of birds on Bedout Island off Western Australia’s Pilbara Coast.

A large body of research shows that seabirds sense strong storms in advance, allowing them to fly away from the tempest or into its calm eye, but the new findings suggest they aren’t invincible, said Jennifer Lavers, lead author of the new paper published in Communications Earth & Environment.

“I’m not calling into question any of that literature,” said Lavers, who coordinates Adrift Lab, an international research group focused on seabirds and marine plastics research, and is also an adjunct researcher at Charles Sturt University in Australia. 

“But I wonder if maybe it’s giving us this false sense of comfort that, when a major storm approaches a seabird breeding island, we say, ‘Don’t worry about it, the birds have got this, they’ll probably flee and go out to the ocean, or they’ll fly directly into the storm.’”

“But it’s not always true,” she said. “There are environmental events that result in very significant mortality,” including the mass seabird deaths documented by her team, which counted brown boobies, lesser frigate birds and an endemic subspecies of the masked booby, and estimated that at least 20,000 individual birds, mostly breeding adults, were killed during the storm.

“What we found on Bedout Island was that the seabirds basically died where they sat,” she said. “There was really no evidence that they attempted to flee. And I don’t have an explanation for that. That’s a hard thing for me.”

When Cyclone Ilsa hit Bedout Island last year after intensifying from category 1 to category 5 strength in less than two days, its 136 mph sustained winds were the strongest on record for Australia.

“I don’t know if that means the storm was too ferocious for the birds,” she said. “It had all the signs of a major storm … but did it just come upon them too quickly? I find that hard to believe.”

When Lavers and her team surveyed the island, they found utter devastation. Nearly every bird on the island died where it was sitting, and in many cases the chicks and eggs were buried by sediment and sand. 

“I don’t really have an answer,” she said. “Maybe for some species, some locations and some storms, wildlife does not have the capacity to respond.”

If tropical storm intensity and frequency increase as projected with global warming, and as recent studies show is already happening, there is cause for concern, she added.

In addition to fueling stronger tropical storms, global warming has also caused extreme marine heatwaves and toxic algae blooms, leading scientists to warn that oceans are facing mass die-offs on a scale that hasn’t happened for millions of years.

Many Impacts Are Undocumented

Seabirds have evolved with disturbances like cyclones, and healthy species can bounce back from mass mortalities But the very high death rate reported by Lavers and her team is concerning, said Ryan Huang, who was not involved in the new study, but researches tropical conservation ecology at the University of Pretoria, and co-authored a 2017 paper on how hurricanes affect migrating seabirds. 

When 90 percent of a local population dies, “it becomes vulnerable to random events like imbalanced sex ratios, illness, or even another disturbance,” he said. “Sometimes it takes just a couple of bad years in a row for a local population to go extinct. The authors are right to highlight concerns about how quickly these birds will recover.”

“Pulse disturbances” like cyclones, droughts and fires can greatly affect population numbers, particularly when species are in a vulnerable part of their life cycle, such as breeding or migrating, he added. In a natural system, species can survive local extinction events like these as long as that habitat can be re-colonized from somewhere else. 

“Unfortunately, if all the other populations are also suffering from climate change effects, or human disturbance makes it harder to disperse, then you have a real problem,” he said. 

“In our work, we found that hurricanes in the Caribbean were the main driver of sooty tern deaths during migration,” he said. Category 5 Hurricane Allen, in 1980, hit during peak migration and may have killed up to half of the population, he added.

“Not all storms have the same consequences; they need to be at the right time and place for mass mortalities,” he said. “Unfortunately, as the climate changes and the frequency of storms increases, you’re rolling the dice more often.”

The impacts of hurricanes and other tropical weather systems in the Caribbean may not even be documented, said Natalia Collier, a seabird ecologist with EPIC, a nonprofit environmental group in the area, who was not involved in the new study.

“There is such a lack of research and monitoring in the region that we often don’t even know if colonies are lost,” Collier said. “Hurricanes have been increasing in intensity in the Caribbean as well.”

Powerful category 5 Hurricane Irma in 2017 may have wiped out a colony of brown pelicans on Saint Martin. Seabirds, she said, “of course, face multiple threats, including development, disturbance and disease, but those are compounded by climate change impacts, which can also result in flooding of low-lying colonies as sea level rises.”

No Time to Recover

Lavers said the potential impact of more frequent severe storms became clear as two other tropical cyclones loomed while she was writing the paper.

“My anxiety level was extremely high. I was like, you’ve got to be kidding me,” she said. “It’s been less than a year since I started writing this paper about Cyclone Ilsa and already, another major cyclone developed off the Pilbara coast, headed toward Bedout Island.”

After weeks of reflection, she realized that seabirds are facing an uncertain future in the “new normal.”

“I thought, if the return interval is so high, it doesn’t even give the scientists studying it ample time to write one paper about one island and make that known to the world before the next cyclone comes through,” she said. “This is the reality, and we’re not only talking about Bedout Island, but so many other seabird hotspots and sea turtle nesting areas.”

Coral researchers have expressed similar concerns that reefs simply are not able to recover because coral bleaching and die-offs are also becoming more frequent, while on land, scientists say that the shorter interval between wildfires poses serious threats to the survival of some forest ecosystems.

Lavers said her study is a warning to prepare for the worst.

“In my 20 years as a seabird ecologist, I have never witnessed anything even remotely comparable to the level of mortality on Bedout Island,” she said. “We lost somewhere between 20,000 and 30,000, breeding-age seabirds in what is essentially the blink of an eye.”

She said that, when her husband returned from aerial surveys, he didn’t want to show her the images at first. 

“He said, ‘You don’t want to see these. I can’t show you these,’ And I was just devastated,” she said. “But I think that scale of mortality is what we’re staring at. We need to be real about that.”