Unlocking animal behavior through motion

Please Note: The 2020 American Physical Society (APS) March Meeting that was to be held in Denver, Colorado from March 2 through March 6 has been canceled. The decision was made late Saturday (February 29), out of an abundance of caution and based on the latest scientific data available regarding the transmission of the coronavirus disease (COVID-19). See our official release on the cancelation for more details.

DENVER, COLO., FEBRUARY 28, 2020 -- Using physics to study different types of animal motion, such as burrowing worms or flying flocks, can reveal how animals behave in different settings. By using principles and technology from fields like fluid mechanics, scientists can track and measure animals in motion. At the 2020 American Physical Society March Meeting in Denver, researchers will present the various ways they quantify animal movement--and subsequently, better understand the animal world.

Social Behaviors in Flocks

Flocks seem to move as one unified organism, with each bird knowing its place and anticipating the group's future movements. Although indistinguishable to the human eye, birds actually modify their flying behaviors based on the type of flock they are flying in.

"You can take the same bird with the same social structure in the same part of the world, and put them into two different contexts. They behave collectively in both cases, but the way they do so is not at all the same," said Nicholas Ouellette, an environmental engineer at Stanford University.

He and his colleagues captured videos of jackdaws, a common species related to crows, flying in two types of flocks: transit flocks were when the birds all flew home to nest at night, while mobbing flocks were when the birds swarmed a predator.

The results indicate jackdaws in transit model their flight pattern after a set number of their neighbors--no matter how close or far those neighbors might be. However, mobbing jackdaws orient themselves by maintaining a set metric distance from surrounding birds. The birds' interactions change based on flock type, suggesting the motives for some types of collective behavior influence animal behavior on an individual level.

Multiple Animals, One Neural Network

It can be difficult to identify and quantify animal behavior in the wild. A neural network developed by Talmo Pereira and his colleagues helps scientists track multiple animals in social settings and monitor their movement.

"The reason why we like to think of behavior in terms of motion is because most of what the brain does is control the body so that it can interact with the world," said Pereira, part of a team in the Center for the Physics of Biological Function and the Neuroscience Institute at Princeton University. The imaging technique uses principles similar to those behind motion capture suits in Hollywood. But unlike actors, animals don't have to wear specialized harnesses. Recently, the team modified their previous tracking method so it can distinguish each animal in a group even during close interactions.

Having a richer representation of animals' movement adds to the quantitative understanding of behavior, according to Pereira.

A Photoelastic Stress Test for Worm Behavior

Deriving quantitative data from behavior requires flexible problem solving. Kelly Dorgan has been studying how marine worms burrow through muddy sediment and the forces they exert.

To replicate sea sediment's physical properties, Dorgan, an ecologist at the Dauphin Island Sea Lab, turned to an unusual substitute. Jell-O has a similar fracture behavior, as sediment. This means that forces exerted by worms burrowing in muds can be directly calculated from forces measured in Jell-O

"Because I could measure forces, I came up with the first realistic measure of the energetic cost of burrowing," said Dorgan. The results showed that despite the strength they use to burrow, worms actually expend very little energy in terms of increased metabolic rate because they move so slowly.