Blue whales are the largest animals in the world, with bodies that can weigh as much as 25 elephants and extend over the length of a basketball court. To support their hulking bodies, the whale use various acrobatic maneuvers to scoop up many individually tiny prey, filtering the water back out through massive baleen plates. In most cases, the whales roll to the right as they capture their prey, just as most people are right-handed. But, researchers reporting in Current Biology on November 20 now show that the whales shift directions and roll left when performing 360° barrel rolls in shallow water.

The findings offer the first evidence of "handedness" in blue whales, the researchers say. They also highlight the importance of studying animals in their natural three-dimensional environments for revealing phenomena that may be impossible to capture in a captive environment.

"We believe that this left-side bias is the result of the whales maintaining a visual connection with their prey with their right eye," says Ari Friedlaender at the University of California, Santa Cruz. "If the whales turned to the right on approach, they would lose sight of their prey and decrease the ability to forage successfully. By rolling to the left, the whales may be maintaining this visual connection to their prey."

"To the best of our knowledge, this is the first example where animals show different lateralized behaviors depending on the context of the task that is being performed," says study co-author James Herbert-Read from Stockholm University in Sweden.

Friedlaender and his colleagues have long studied blue whales' feeding behaviors in an attempt to understand how they can support their large bodies. In the new study, the researchers attached motion-sensing tags to 63 blue whales living off the coast of California to capture how the animals move as they engulf their prey.

In total, the researchers collected data on more than 2,800 rolling lunges for prey to find that the animals approach their prey using two different rolling behaviors. In some cases, they roll to the side and then back, turning 180° or less. In other cases, they go in for a complete barrel roll that takes them around full circle.

The evidence shows that individual whales have a preference as to whether they roll to the right or the left. The vast majority of the whales showed a preference for rolling to the right, much as more people show a preference for using their right hands. But, the whales also showed some flexibility in their approach. When the animals did a barrel roll in shallow water to attack a small patch of prey from below at a steep angle, they more often spun left, going against their general preference.

The findings are the first to demonstrate a left-side bias for a lateralized routine behavior, the researchers say. They also highlight blue whales' adaptability when it comes to feeding behaviors. The whales shift their foraging strategies depending on where they are feeding in the water column, how their prey are behaving, and how they need to maneuver to forage successfully.

"We were completely surprised by these findings, but when considering the means by which the whales attack smaller prey patches, the behavior really seems to be effective, efficient, and in line with the mechanisms that drive their routine foraging behaviors," Friedlaender says.

"While most other large baleen whales that lunge-feed can feed on both krill patches and small forage fish like anchovies and herring, blue whales feed almost exclusively on krill patches and seem to exhibit feeding strategies to maximize their intake of as many krill as possible with each energetically costly feeding event," adds co-author Dave Cade at Stanford University.

The researchers say the next step is to conduct similar studies on related species of whales to understand whether the behaviors seen in blue whales also exist in them. They're also developing new technologies to capture even finer details of the whales' underwater movements.