Global warming: More hurricanes kill more seabirds

On April 13, 2023, Cyclone Ilsa, a Category 5 tropical cyclone, hit Bedout Island, which is just 17 hectares in size. The island off the coast of northwest Australia is remote and little explored. Tropical cyclones are not uncommon here – animals and people are prepared for the harsh nature and the harsh climate. But Storm Ilsa, which hammered northern Western Australia with winds of up to 260 kilometers per hour, hit the island’s populations of several seabird species particularly hard.

An Australian study published at the beginning of June in the specialist magazine »Communications Earth & Environment« was published, documented. The researchers, led by Jennifer Lavers, an associate research scientist at Australia’s Charles Sturt University, examined aerial photographs and soil samples taken between April 17 and July 21, a few days after the storm, and then over a period of three months, were collected. The researchers analyzed the percentage mortality of three species: the white-bellied booby (Sula leucogaster), the ariel frigatebird (Fregata ariel) and an endemic subspecies of the masked booby (Sula dactylatra bedouti).

At least 20,000 dead birds

The storm was an exceptional situation – for people and animals alike, as Lavers remembers. Her husband Andrew, who is a co-author of the article, was living in Port Hedland, a town in the Pilbara region of Western Australia, over 1,600 kilometers north of Perth, at the time of the cyclone. The city was closed and neither of them took their eyes off the weather forecast for a moment, said Lavers. They were aware that both places – the city and Bedout Island off the coast – would “suffer significant damage” from the cyclone.

In fact, the results of the subsequent analysis on the island should shock the researchers: Based on their observations, the study authors estimate that 80 to 90 percent of the bird populations examined – at least 20,000 birds – were killed during the storm. Adult breeding birds were obviously particularly affected. The latter perhaps also explains the high number of deaths. Normally, seabirds “can detect approaching storms due to the significant drop in pressure,” explained Lavers. But instead of fleeing, the birds stayed put. One reason for this may have been that they were in the middle of the peak breeding season and “therefore may have been reluctant to leave their eggs or their chicks behind.” However, to say this with absolute certainty, further studies would be needed, according to Lavers.

Coral reefs are also suffering

To date, Australia has an average of eleven tropical cyclones in its region every year. These have negative effects on a range of organisms – another example is the coral reefs off the coast of northwest and northeast Australia. However, there has been little research into the effects on seabird populations. The study by Lavers and her colleagues now makes it clear that such weather extremes can cause mass extinctions, but can also disrupt the birds’ nesting and breeding patterns as well as migration strategies.

Since it is now known that global warming is increasing both the intensity and the frequency of such tropical cyclones, the study authors explicitly warn about the dangers that seabirds are exposed to as a result. Since many seabirds normally live relatively old, have long generation times and only raise very few chicks per year, they cannot cope with significant population loss as well as some other species.

For example, while three months after the storm there were indications that vegetation on the island was beginning to recover, there were only minimal developments in seabird populations, Lavers reported. “That’s why the return interval of cyclones is so important.” More storms at shorter intervals would mean “that seabirds and other wild animals have less and less time to recover between big storms,” ​​explained the researcher. “These are not good news.”

According to the study, population losses in seabirds can also have direct consequences for an island’s ecosystem, as seabirds transport nutrients from the sea to land with their droppings.