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Foraging habits of seabirds altered by turbulent tidal flows

Water currents caused by the tide have a major influence on the foraging behavior of seabirds, according to a study from the University of Plymouth. The researchers investigated how terns respond to turbulent tidal flows caused by natural coastal features and man-made structures.

The scientists used drones to experience what the terns see and how their behavior changes depending on the movement of tidal flows beneath them.

The study was focused on a turbulent tidal channel, Strangford Lough in Northern Ireland, which is known to be a foraging hotspot for terns.

The experts found that the terns were more likely to actively forage over swirling patches of water, or vortices. However, eruptions of upwelling water ahead of the terns’ flight path prompted them to stay on course as they approached.

The researchers said their findings offer a never-before-seen insight into how tidal turbulence can impact foraging behaviors. The experts noted that the study may ultimately help to predict how species will respond to environmental changes such as the increased future development of ocean renewable energy sites.

“Our research highlights the importance of identifying changes in local flow conditions due to ocean energy structures which can change the occurrence, scale and intensity of localized turbulence in the water,” said Dr. Lilian Lieber. 

“Through a fantastic interdisciplinary collaboration, we were able to track prevalent flow features and seabirds on thus far unobtainable scales, shedding new light on tern foraging associations with turbulence.” 

“We found that terns were more likely to actively forage over vortices, while conspicuous upwellings provided a strong physical cue even at some distance, leading them to investigate such features. This research can help us predict seabird responses to coastal change.”

“It is extremely exciting that we now have these incredibly detailed animal movement data, which allows us to investigate behavioral processes at effectively arbitrarily fine scales of animal decision-making,” said Professor Roland Langrock.

“While it presented some new statistical challenges, the interdisciplinary nature of our project presents a valuable contribution to the emerging field of high-throughput movement ecology.”

Dr. Alex Nimmo-Smith used machine learning and mapped the underlying turbulent features to track the terns.

“The drone provided a real bird’s eye view, allowing us to track the highly localized foraging behavior of the terns and the close association they have with particular flow features.”

“Upwelling boils and swirling vortices, characteristic of strong tidal flows, can bring potential prey items (such as small fish) to the water surface and trap them there. Therefore, these physical processes provide foraging opportunities for the terns.”

The study is published in the journal Royal Society Proceedings B.

By Chrissy Sexton, Staff Writer

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