Drone footage provides new insight into gray whales' acrobatic feeding behavior

The whales' movements, including forward and side-swimming, headstands and the use of "bubble blasts" change as the whales grow, said Clara Bird, a researcher in the Marine Mammal Institute's Geospatial Ecology of Marine Megafauna Laboratory.

Using drone footage captured over seven years, Bird quantified the gray whales' behavior and their individual size and body condition. She found that the probability of whales using these behaviors changes with age.

Younger, smaller whales are more apt to use forward swimming behaviors while foraging. Older, larger whales are more likely to headstand, a head-down position where the whale is pushing its mouth into the ocean floor. The probability of whales using these behaviors changes with age.

"Our findings suggest that this headstanding behavior requires strength and coordination. For example, we often see whales sculling much like synchronized swimmers do while they are headstanding. It is likely this behavior is learned by the whales as they mature," said Bird, who led the research as part of her doctoral dissertation. "We have footage of whale calves trying to copy this behavior and they're not able to do it successfully."

The findings were just published in two new papers authored by Bird and co-authored by Associate Professor Leigh Torres, who leads the GEMM Lab at Hatfield Marine Science Center in Newport.

Since 2015, Torres and her research team have been studying the health and habits of the Pacific Coast Feeding Group, a roughly 200-member subgroup of whales who spend their summers feeding off the coast 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 Eastern North Pacific population do. These whales face elevated exposure to human activities in some locations, including boat traffic, noise and pollution, while they feed in the shallow waters along the Pacific Northwest Coast.

"It's been an amazing journey of discovery over the last 10 years learning about how cool these gray whales are. They are underwater acrobats, doing tight turns, upside-down swimming and headstands," Torres said. "We have now connected these behaviors with the habitat, size and age of the whale, which allows us to understand much more about why they go where they go and do what they do. This will help us protect them in the long run."

The new study shows that whales are changing foraging tactics depending on the habitat and depth of the water they are in. For example, they are more likely to use headstanding when they are on a reef, because their primary prey, mysid shrimp, tend to aggregate on reefs with kelp, Bird said.

The researchers also investigated why the gray whales perform "bubble blasts" -- a single big exhale while they're underwater that produces a large circle pattern at the surface.

"While it was thought that bubble blasts helped gray whales aggregate or capture prey, our study shows that bubble blasts are a behavioral adaptation used by the whales to regulate their buoyancy while feeding in very shallow water," Torres explained.

Larger, fatter whales were more likely to bubble blast, especially while performing headstands. The bubble blasts also were associated with longer dives, supporting the hypothesis that the behavior helps whales feed for a longer period of time underwater.

"It is just like when we dive underwater, if we release air from our lungs, then we can stay underwater more easily without fighting the buoyancy forces that push us back toward the surface," Bird said.

Together, the two papers provide new insight into how whales' size affects their behavior and the role social learning may play in whales' adoption of these behaviors, she said.

"Because these whales are feeding close to shore, where the water is shallow and we can capture their behavior on video, we're able to really see what is happening," Bird said. "To be able to study the whales, in our backyard, and fill in some answers to questions about their behavior, feels very special."