brown booby

 

Increased tropical cyclones due to global warming could lead to dramatic declines in seabird populations, a new study warns.

Scientists observed that after Cyclone Ilsa, a category-5 storm, struck Bedout Island in Western Australia in April 2023, seabird populations at this critical breeding site collapsed by 80-90%.

Published in the journal Communications Earth & Environment, the study highlights that such losses could be unsustainable for seabird populations as cyclones become more frequent and intense due to global heating. The extreme winds, heavy rains, and massive swells from these storms disrupt seabird breeding cycles.

Seabirds play a vital role in maintaining tropical reef ecosystems, and their loss could add further stress to these environments.

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’s 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 recovery will be slow and likely interrupted by another cyclone event.”

Researchers conducted aerial and ground surveys to estimate the mortality rates of three seabird species—the brown booby (Sula leucogaster), the lesser frigatebird (Fregata ariel), and an endemic subspecies of the masked booby (Sula dactylatra bedouti)—in the months following the cyclone.

The surveys revealed that at least 20,000 birds, primarily breeding adults, were lost on the 17-hectare (42-acre) Bedout Island. The Bedout masked booby, which is unique to this island, was particularly affected.

Researcher Jennifer Lavers emphasised that Bedout’s situation has broader implications for seabirds worldwide.

While it is normal for tropical cyclones to impact wildlife, including seabirds, the increasing frequency and severity of these storms in a warming world could hinder seabird populations’ ability to recover.

“The mortality that we’ve seen is unprecedented,” said Dr Alex Bond, the principal curator of birds at the Natural History Museum. “The cyclone hit in April, which is a reasonably peak time when lots of seabirds were nesting.

“We were able to do counts of the bodies and we estimated that basically all the brown boobies and practically all the masked boobies had been killed by Cyclone Ilsa.”

Cyclone Ilsa recorded winds of at least 135 mph (217 km/h) before making landfall on Western Australia and Bedout Island.

Bond said: “The important thing to remember is that these birds have evolved in areas with cyclones. That’s not the issue here.

“The problem is twofold: number one was just the intensity of the storm. This was the strongest cyclone to hit Australia, and we’re going to see more of that as one of the consequences of the global climate breakdown. The other issue is the recovery time.”

 

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