Drone footage offers new insight into acrobatic feeding behavior of gray whales

Drone footage captured by researchers at Oregon State University’s Marine Mammal Institute offers new insight into the acrobatics of gray whales as they forage for food in waters off the coast of Oregon.

Whale movements, including forward and sideways swimming, headstands and use of “bubble jets,” change as the whales grow, said Clara Bird, a researcher in the Marine Mammal Institute’s Marine Megafauna Geospatial Ecology Lab.

Using drone footage taken over seven years, Bird quantified gray whale behavior, individual size and fitness. She found that the likelihood of whales engaging in these behaviors changed with age.

Younger, smaller whales are more likely to swim forward when searching for food. Older, larger whales are more likely to perform headstands, a position where the whale presses its mouth into the ocean floor. The likelihood of whales using these behaviors changes with age.

“Our results suggest that this head-down behavior requires strength and coordination. For example, we often see whales rowing like synchronized swimmers do when they stand on their heads. It is likely that this behavior is learned by the whales as they grow,” said Bird, who led the research as part of his doctoral thesis.

“We have images of calves trying to copy this behaviour but they can’t do it.”

The findings have just been published in two new papers authored by Bird and co-authored by Associate Professor Leigh Torres, who heads the GEMM lab at the Hatfield Marine Science Centre in Newport. The paper on the behaviour of the bursting bubbles was published in Ecology and evolution.

Since 2015, Torres and his research team have been studying the health and habits of the Pacific Coast Feeding Group, a subgroup of about 200 members that spends their summers feeding off the coasts of Oregon, Washington, northern California and southern Canada, rather than traveling north to the Arctic as most of the 19,000 gray whales in the Northeast Pacific population do. These whales are exposed to high levels of human activity in some locations, including ship traffic, noise and pollution, as they feed in shallow waters along the Pacific Northwest.

“It’s been an incredible journey of discovery over the last 10 years, where we’ve learned just how awesome these gray whales are. They’re underwater acrobats, doing tight turns, swimming upside down and doing handstands,” Torres said.

“We have now linked these behaviours to the habitat, size and age of the whale, which gives us a better understanding of why they go where they go and do what they do. This will help us protect them in the long term.”

The new study shows that whales change their foraging tactics depending on the habitat and depth of water they’re in. For example, they’re more likely to use the standing position when on a reef because their primary prey, mysis shrimp, tends to congregate on reefs with kelp, Bird said.

The researchers also studied why gray whales perform “bubble bursts”: a single large exhalation while underwater that produces a large circular pattern on the surface.

“While bubble bursts were previously thought to help gray whales group together or capture prey, our study shows that bubble bursts are a behavioral adaptation used by whales to regulate their buoyancy when feeding in very shallow waters,” Torres said.

Larger, fatter whales were more likely to blow bubbles, especially when doing handstands. Bubbles were also associated with longer dives, supporting the hypothesis that this behavior helps whales feed longer underwater.

“It’s like when we dive underwater, if we release air from our lungs, we can stay underwater more easily without fighting the buoyancy forces pushing us back up to the surface,” Bird said.

Together, the two papers shed new light on how whale size affects their behavior and the role that social learning may play in whales adopting these behaviors, she said.

“Because these whales feed close to shore, where the water is shallow and we can film their behavior, we can really see what’s going on,” Bird said. “Being able to study the whales, in our backyard, and answer some questions about their behavior is pretty special.”

The article on gray whale foraging tactics was published in the journal Animal behavior. Co-authors of this paper are KC Bierlich, Marc Donnelly, Lisa Hildebrand, and Alejandro Fernandez Ajó of the GEMM lab at the Marine Mammal Institute; Enrico Pirotta of the University of St. Andrews; and Leslie New of Ursinus College in Pennsylvania. Other co-authors are Bierlich, Hildebrand, Fernandez Ajó, Pirotta, and New.