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New study shows that seabirds chase away tropical cyclones

New study shows that seabirds chase away tropical cyclones

Graphic summary. Photo credit: Current Biology (2024). DOI: 10.1016/j.cub.2024.06.022

A new study published today Current Biology, “Oceanic Seabirds Prey on Tropical Cyclones” reveals that the rare desert petrels (Pterodroma deserta), a widespread seabird in the North Atlantic, exhibit unique foraging behaviors during hurricane season.

Unlike other pelagic seabirds, these petrels do not avoid intense tropical cyclones but use the dynamic conditions to their advantage, providing new insights into the impacts of cyclones on marine life in the open ocean.

“Initial studies suggested that seabirds either fly around cyclones or seek refuge in the calm eye of the storm. However, the desert petrels we tracked did neither; instead, a third of them followed the cyclone for days, traveling thousands of kilometers,” explained Francesco Ventura, lead author and postdoctoral researcher in biology at the Woods Hole Oceanographic Institution (WHOI). “When we saw the data, we almost fell off our chairs. This is the first time we have observed this behavior.”

“It is remarkable how well the birds can exploit the large-scale wind conditions over the North Atlantic for their travels,” said Caroline Ummenhofer, Associate Scientist for Physical Oceanography at WHOI. “If you overlay the foraging behavior of the petrels with the average winds, there is a very good correspondence.”

Desertas petrels nest on the Portuguese island of Bugio, off the west coast of North Africa. This island is home to the only known breeding colony of these pigeon-sized seabirds in the world. Fewer than 200 pairs live on a plateau surrounded by steep cliffs.

During their six-month breeding season, Desertas petrels engage in extraordinary foraging expeditions, often spending weeks at sea and flying up to 12,000 kilometers round trip across the Atlantic in search of food. They belong to the genus Pterodroma, which means “wings in flight.”

“We linked the birds’ locations to increasing storm conditions, including waves up to eight meters high and wind speeds of 100 kilometers per hour,” Ventura said.

“In strong winds, birds reduced their ground speed, probably because they spent less time in flight to avoid injury to their wings. In addition, the aftermath of the storms provided predictably favorable wind conditions with stronger tailwinds than alternative routes. Impressively, none of the birds we tracked were injured by the storms and there were no cases of nest abandonment.”

The petrels hunt small fish, squid and crustaceans that normally live at depths of 180 to 900 meters. Since they cannot dive to such depths, these seabirds must wait for their prey to rise closer to the surface at nightfall.

“As we have now discovered, desert petrels follow hurricanes where prey has accumulated closer to the surface in the wake of the storms,” ​​said Ummenhofer.

The study shows that cyclone wakes provided improved foraging conditions, with large decreases in sea surface temperature and a significant increase in surface chlorophyll. These changes indicate increased ocean mixing and productivity, likely increasing the abundance and accessibility of prey for surface-feeding petrels.

“One of the interesting aspects of the interaction between a tropical cyclone and the ocean is the intense vertical mixing in the upper ocean layers caused by very strong winds and huge surf waves,” said Philip Richardson, professor emeritus of physical oceanography at WHOI and co-author of the study.

“The cyclonic winds can cause a divergence in the upper layer, moving cooler, deeper water to the surface.”

“The cyclones provide an extremely valuable foraging opportunity for desert petrels because the storms stir up mesopelagic prey from deep in the vertical column, providing the seabirds with an easy meal at the surface,” Ventura explained.

“While storms are generally considered destructive, especially in coastal areas, our research shows that storm-induced dysfunction can create new opportunities. We expand our understanding of how petrels navigate the open ocean in search of food.”

“We now have a new perspective on the impacts of hurricanes on marine ecosystems from the perspective 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.”

Although cyclones are known to dramatically affect ocean and coastal ecosystems, their impacts on pelagic marine life are poorly understood. This research shows how higher predators such as desert petrels adapt their foraging strategies to the dynamic marine environment and use cyclone-induced oceanographic changes to their advantage.

More information:
Francesco Ventura et al, Oceanic seabirds prey on tropical cyclones, Current Biology (2024). DOI: 10.1016/j.cub.2024.06.022

Provided by Woods Hole Oceanographic Institution

Quote: New study shows seabirds hunt tropical cyclones (July 9, 2024), accessed July 10, 2024 from https://phys.org/news/2024-07-reveals-oceanic-seabirds-tropical-cyclones.html

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