A groundbreaking study has revealed that Desertas petrels (Pterodroma deserta), a rare but wide-ranging seabird in the North Atlantic, actively seek out tropical cyclones to help them survive.
Researchers from the Woods Hole Oceanographic Institution (WHOI) say this unique behaviour, which is all to do with food, provides new insights into the impact of cyclones on open ocean marine life.
Desertas petrels nest on the steep cliffs of Bugio Island just off the western coast of North Africa. It's the only known nesting colony of these rare, crow-sized seabirds in the world.
Desertas petrels belong to the genus Pterodroma, which means "wings on the run." It's an appropriate name for the species, which often spends weeks on end at sea in search of food. Some individuals clock up a remarkable 7,500 miles on roundtrips across the Atlantic.
But distance isn't the only thing that makes these journeys impressive. Scientists now believe that Desertas petrels exploit tropical cyclones during hurricane season to enhance their catch.
"Initial studies suggested that seabirds either circumnavigate cyclones or seek refuge in the calm eye of the storm," said Francesco Ventura, lead author of the study published in Current Biology.
"However, the Desertas petrels we tracked did neither; instead, one-third of them followed the cyclone for days, covering thousands of kilometres.
"When we saw the data, we nearly fell off our chairs. This is the first time we have observed this behaviour."
"It's striking how well the birds know how to exploit the large-scale wind conditions over the North Atlantic for their travels," added Caroline Ummenhofer, Associate Scientist and Physical Oceanography at WHOI.
"When you overlay the petrels' foraging trips on top of average winds, it's a very close match."
"We correlated the birds' locations with intensifying storm conditions, including waves up to eight metres high and wind speeds of 100 kilometres per hour," said Ventura.
"Upon encountering strong winds, the birds reduced ground speed, likely by spending less time in flight to avoid injury to their wings. In addition, the wakes of the storms provided predictably favourable 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."
So, why do Desertas petrels chase cyclones?
The Desertas petrel's diet is made up of small fish, squid and crustaceans. Typically, these animals live between 600 to 3,000 feet beneath the surface of the water – too far down for the petrels to hunt. Instead, they wait until nightfall when their prey ascends to shallower depths.
"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 study shows that in the wake of a cyclone the surface temperature of the sea drops dramatically. There is also an increase in surface chlorophyll. As a result, there is more ocean mixing and productivity increases, attracting prey to the surface in easy reach of the petrels.
"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," said Philip Richardson, Physical Oceanography at WHOI and a co-author on the paper.
"The cyclonic winds can cause a divergence in the upper layer that moves cooler, deeper water toward the surface."
"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," explained Ventura.
"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."
Find out more about the study: Oceanic seabirds chase tropical cyclones
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