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07-09-2024

Riders on the storm: Why some seabirds chase cyclones

A recent study reveals that while some seabirds are scrambling to avoid tropical cyclones, others are actually chasing these storms for days at a time. 

Desertas petrels, scientifically known as Pterodroma deserta, are seabirds found primarily in the North Atlantic. According to the researchers, these birds engage in unique foraging behaviors during the hurricane season. 

The experts discovered that Desertas petrels exploit the dynamic conditions of intense tropical cyclones for their benefit.

Riding the wind 

Study lead author Francesco Ventura is a postdoc investigator in biology at the Woods Hole Oceanographic Institution (WHOI). 

“Initial studies suggested that seabirds either circumnavigate cyclones or seek refuge in the calm eye of the storm. However, the Desertas petrels we tracked did neither; instead, one-third of them followed the cyclone for days, covering thousands of kilometers,” said Ventura.

“When we saw the data, we nearly fell off our chairs. This is the first time we have observed this behavior.”

“It’s striking how well the birds know how to exploit the large-scale wind conditions over the North Atlantic for their travels,” said Caroline Ummenhofer, associate scientist at WHOI. “When you overlay the petrels’ foraging trips on top of average winds, it’s a very close match.”

Wings on the run

Desertas petrels make their nests on Bugio Island in Portugal, just off the western coast of North Africa. This island is special because it’s the only place in the world where these pigeon-sized seabirds are known to nest. There are fewer than 200 pairs, and they live on a plateau surrounded by steep cliffs.

During their six-month breeding season, Desertas petrels embark on incredible foraging trips. They can spend weeks at sea, flying up to 7,500 miles across the Atlantic to find food. These birds belong to the genus Pterodroma, which fittingly translates to “wings on the run.”

Seabirds chasing cyclones

Ventura said the team correlated the birds’ locations with intensifying storm conditions, including waves up to 8 meters high and wind speeds of 100 kilometers per hour.

“Upon encountering strong winds, the birds reduced ground speed, likely by spending less time in flight to avoid injury to their wings,” noted Ventura.

“In addition, the wakes of the storms provided predictably favorable wind conditions with higher tailwind support than alternative routes. Impressively, none of the birds we tracked were harmed by the storms and there was no incidence of nest desertion.”

Cyclone wakes improve foraging conditions 

The diet of the Desertas petrel consists mainly of squid, fish, and crustaceans, which they catch by surface seizing. Because the birds cannot dive to great depths, they hunt at nightfall when their prey moves within reach. 

“As we’ve now discovered, Desertas Petrels follow hurricanes where prey have accumulated closer to the surface in the wakes of the storms,” said Ummenhofer.

The experts found that cyclone wakes improve foraging conditions for the petrels. Enhanced ocean mixing and productivity seem to boost prey abundance and accessibility.

“One of the interesting aspects of the interaction of a tropical cyclone and the ocean is the intense vertical mixing in the upper ocean layers caused by very strong winds and huge breaking seas,” noted study co-author Philip Richardson, an expert in physical oceanography at WHOI.

“The cyclonic winds can cause a divergence in the upper layer that moves cooler, deeper water toward the surface.”

A fresh perspective on seabirds and cyclones

Ventura explained that the cyclones present a highly valuable foraging opportunity for Desertas petrels because the storms churn up mesopelagic prey from deep within the vertical column, giving the seabirds an easy meal at the surface. 

“While storms are typically seen as destructive, particularly in coastal areas, our research reveals that functional perturbance driven by storms can create new opportunities. We’re advancing our understanding of how petrels navigate the open ocean to find food.”

“We now have a fresh perspective on hurricanes’ impact on marine ecosystems through the eyes of an apex predator,” said Ummenhofer. “This study provides valuable insights into the resilience and foraging strategies of pelagic seabirds in the face of extreme weather events.”

The research is providing new insights into the impact of cyclones on open ocean marine life.

Despite their destructive nature onshore, cyclones may have positive net effects on the demography of many mid-latitude pelagic seabirds and, likely, other marine top-predators, concluded the researchers.

The study is published in the journal Current Biology

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