Birds of a feather flock to bad weather: Study reveals how seabirds chase cyclones
Featured image caption: The Desertas Petrel, shown here, spends weeks at a time foraging for food on the open ocean. A recent study uncovers a never-before-seen behavior in these birds of chasing dangerous tropical storms to eat from the churning, turned-over ocean waters. (Image source: ‘Pterodroma feae’ by jsterling60, CC-BY-NC 4.0, via iNaturalist)
Source article: Ventura F, Sander N, Catry P, Wakefield E, De Pascalis F, Richardson P L, Granadeiro J P, Silva M C, Ummenhofer C C. Oceanic seabirds chase tropical cyclones. Current Biology (2024). DOI: 10.1016/j.cub.2024.06.022
For most birds, bad weather is just that: bad. But for the Desertas Petrel, it’s an opportunity that no one else is willing to take. Desertas Petrels are a relatively rare subspecies of seabird that nest on Bugio Island in Portugal off the coast of North Africa, where just under 200 pairs reside on rocky cliffs and plateaus during the breeding season. These birds often spend weeks at a time in flight over the north Atlantic ocean to forage for food, flying up to 7,500 miles round trip back to the nesting colony.
This region of the Atlantic ocean is not only home to these birds, but also to intense tropical storms in the summer and fall seasons. Cyclones cause major disturbances to both land and ocean habitats with strong winds and rainfall. For most seabirds, cyclones are particularly disruptive because they force birds to move inland or to less desirable habitats to avoid the worst effects of the storm. Some birds cope with this stress by staying close to coastal areas, moving around the cyclone’s edge, or even flying toward the eye of the storm where conditions are calmer. Researchers from the Woods Hole Oceanic Institute in Massachusetts and their collaborators explore how Desertas petrels respond to cyclone activity, and further investigate why these birds exhibit a strikingly different behavior than expected.
A taste for tempests: Petrels intentionally follow behind cyclones
To find out how cyclones impact open-ocean-feeding birds, the researchers compared historical cyclone movement with GPS tracking data from the Desertas petrel population. They mapped the paths and intensities of tropical storms in the northern Atlantic for four breeding seasons in 2015, 2016, 2017, and 2019. Petrel movement was tracked over the same four years using lightweight GPS devices attached to the birds, which revealed where they traveled from their nesting island in search of food.
While researchers expected these birds to avoid cyclones or seek calmer conditions when storms approached, overlaying the petrel’s flight paths with the trajectory of the storms revealed the opposite pattern. The petrels intentionally followed cyclones – sometimes for thousands of kilometers – and often remained within 200 kilometers behind the center of the storm, demonstrating a behavior never seen before in pelagic seabirds.
Overall, researchers analyzed 43 petrel flights from 33 individual birds starting from their nesting location on Bugio Island. For nearly half of those flights, birds flew within a 200 kilometer distance from the eye tropical cyclone where they encountered wind speeds up to 86 kilometers per hour (53 miles per hour) and choppy oceans with waves reaching over 6 feet.
Tropical storms are common in the north Atlantic ocean, particularly between June and November. Desertas petrels nest off the coast of north Africa and spend much of their time searching for food on the open ocean. Instead of avoiding high winds and choppy seas, the birds follow the wake of the storms, sometimes for thousands of kilometers. (Image source: “Tropical Storm Jose” by Rob Gutro, NASA Goddart Space Flight Center, CC-BY-2.0, via Flickr)
The GPS doesn’t lie: birds are seeking out these storms. But why would the petrels choose to follow such perilous weather conditions? One hypothesis posited that more intense winds following the storm could support the birds in flight and increase their energy efficiency for traveling long distances. Further analysis of the wind patterns alongside the petrels’ GPS tracks supported this idea, though the birds still preferred flight paths closer to the storms when the option was available. Another idea supposed that it’s not about how the birds handle bad weather conditions, but about how the storm disturbance is actually providing a beneficial service by stirring up the ocean – and the creatures that live within.
Gale force gourmet: Winds stir up a tasty sea creature buffet
The wake of a storm provides a buffet of options for the petrels. Cyclones alter the ocean surface by increasing mixing between the surface and deeper waters, bringing creatures like small fish, squid, and crustaceans that can live hundreds to thousands of feet below the surface. Investigating further, researchers also found changes to surface temperatures and chlorophyll concentrations in the wake of storms that could support abundant prey that are easily accessible to the petrels. While cyclones may seem destructive, they actually create a bountiful feast for seabirds that are willing to risk flying close to these storms. For petrels, the evidence suggests that the benefits are worth the cost.
Many seabirds may be able to sense weather cues like changes in temperature, pressure, wind direction, precipitation, and wave height to detect gathering or incoming storms. While some may use this information to avoid storms altogether, it seems that for the Desertas petrel, these are navigatory cues to follow towards food. These birds follow cyclones much more frequently and closely than researchers would expect by random chance. Contrary to expectation, these birds are not avoiding or fleeing storms, or even seeking shelter in the eye, but taking advantage of an opportunity to follow the wake of disturbed waters and upheaved prey creatures.
A Desertas petrel in flight. One proposed reason why these seabirds chase cyclones is to reap the benefit from the disturbed oceans. The storms churn ocean waters, bringing deeper-dwelling creatures such as small fish, squid, and crustaceans to the surface where they are easily available for petrels to eat. (Image source: “Desertas Petrel” by Christoph Moning, CC-BY 4.0, via iNaturalist)
Charting new courses: Future directions for behavioral and environmental research
This study inspires new directions for research for both this rare bird population, but also for investigating the impacts of tropical storms on the open ocean. For the Desertas petrel, understanding how and where these birds search for food is critical information to protect this vulnerable population and the food sources they use. While no other species of birds is known to demonstrate this storm-chasing behavior, the knowledge that this could be an effective strategy might lead to discovering other species that also engage in this type of behavior in marine or even terrestrial systems.
In addition to the new behavioral strategies uncovered here, more information is needed on environmental impacts of oceanic storms. The majority of cyclone research is centered around how they affect coastal systems in part because they have larger impacts on human settlements and critical natural habitats along coastlines. Less is known about how they impact open-ocean sea life. This work is important to understanding how apex predators like seabirds sustain themselves on a diet from open surface waters with seemingly limited food options. It also suggests that disturbances like cyclones are not always wholly negative – they can actually increase ocean productivity and sustain biodiverse networks of predators and prey.
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