Drone video of gray whales offers new insights into their diet

Drone videos of gray whales taken over seven years off Oregon have revealed new details about how the giant marine mammals find and eat food.

Among the findings, described in two studies published this summer, are that gray whales use different swimming techniques to gather food depending on their size and age, and that larger whales are more likely to emit “bubble bursts” to stay underwater.

“Before this study, we thought that every whale engaged in one of these behaviors,” said lead author of both studies, Clara Bird, a researcher at the Marine Mammal Institute at Oregon State University. “Nobody really thought there was a pattern to who did what behavior.”

Bird's research also found that whales use different feeding techniques depending on the depth of the water in which they forage and the habitats of their prey. Such information could aid future conservation efforts, she said, by providing insights into the types of habitats that may need to be protected to preserve whales' access to food.

“Although we're not actively trying to protect specific habitats right now, it's really important to know that whales of different ages may not all use the same habitat for future problems,” Bird said. “It will help us manage them in the future.”

A portion of the gray whale population is listed as endangered under the Endangered Species Act. The entire species was once threatened with extinction due to commercial hunting. Once common in the Northern Hemisphere, gray whales are now only regularly spotted in the North Pacific. Nearly 27,000 were estimated to be in the area in 2016, according to a 2020 report from the National Oceanic and Atmospheric Administration.

The whales eat amphipods such as tiny shrimp and worms, which they consume by sucking up water and sediment from the ocean floor where these animals live and then using their baleen to filter the food. Gray whales are typically observed alone or in small groups, although large groups can also be seen at feeding or breeding grounds.

Bird and her team conducted their research off Newport. On sailing trips over seven years, the group tracked and documented individual whales with drones. They identified specific whales based on distinguishing features such as scars, spots or tail shape.

The first study resulting from this work, published in July in the journal Animal Behavior, focused on differences in whale foraging behavior depending on size and habitat.

The team tracked 78 gray whales from 2016 to 2022, with a total of 160 sightings. In the drone video, they observed that younger, smaller whales often swam sideways or facing forward, opening and closing their mouths to find and consume food. Older, larger whales, on the other hand, tended to dive and then stay in place upside down, which the scientists called the “headstand technique.”

The likelihood of such a headstand increased as a whale grew larger, the study found, while the likelihood of the forward swimming tactic decreased. The depth of the water and the type of habitat – rocky, sandy or coral reef – also played a role in the whales' approaches.

Bird attributes the switching between techniques to the maturity of the whale's muscles as well as his level of strength and coordination.

Her team's second study, published in August in the journal Ecology and Evolution, described how older, larger whales release air from their blowholes to stay underwater while foraging.

The “bubble bursts” can help a whale sink by reducing its buoyancy. Larger whales have a greater need for it because their larger lungs hold more air and they have more blubber, making them more vulnerable to swimming.

The finding was based on observations of 75 whales. On average, bubble explosions occurred 27 seconds after a whale dived to feed, and most were observed while the whales were doing headstands. The older and larger a whale became, the greater the likelihood of such an explosion.

“This kind of pairing of size with behavior at the individual level is a really exciting part of this study,” Bird said.

Susan Parks, a biology professor at Syracuse University who has published studies on whale eating habits but was not involved in the new research, said documenting diversity within a whale species helps scientists avoid inaccurate generalizations.

“As we look to protect endangered species, it's really important to understand that there can be big differences in behavior,” Parks said. “So we can’t just stop at individual observations.”

Parks also highlighted the potential of drones for collecting detailed data on whales.

“There is so much unknown about their behavior,” she said, adding that the study shows how “using drone footage to essentially spy on what the whales are doing gives them a completely different perspective on the details of their livelihoods .”