Gentoo penguins call to each other so they can stick together and hone in on prey while foraging for krill in the sea, a study of more than 200 hours of penguincam footage reveals. It is one of the most comprehensive studies to use a penguin-borne camera to date.

The penguins have a special call that they use offshore compared with their land-based communications, finds the study, published in Scientific Reports. How penguins call to each other at sea has been a mystery for many years due to the difficulty of listening in when the penguins are off swimming and diving in the wild.

"When engaged in group behaviours, individuals use a diverse repertoire of calls. Calls may enable group-living birds to exchange information, gather group members, and coordinate group movements across various contexts," the researchers, led by Noori Choi of the Korea Polar Research Institute and the University of Nebraska, wrote in the study.

A total of 26 adult gentoo penguins were monitored for two breeding seasons between 2014 and 2016. The scientists captured them just after leaving their nests on the way to the ocean. They attached video cameras to the heads and bodies of each penguin, before releasing them. The cameras rolled for eight hours before running out of power.

Nearly 600 individual penguin calls were recorded. Almost half of these seemed to be regrouping calls, leading to penguins coming together within one minute. After a call the penguins spent less time diving and more time heading over to where the calling penguin was, the researchers found.

It's thought that grouping together while feeding could help the penguins feed. Their prey – 99% of which is Antarctic krill – move in swarms. When one penguin comes across a swarm, calling in the rest of the group could maximise their hunting ability.

Gentoo penguin
A gentoo penguin sporting a camera on its head. Won Young Lee

But the other half of calls didn't immediately result in penguins grouping. Exactly what the penguins were communicating with these calls is not yet known. Further study of penguins in the wild could shed more light on this and other kinds of penguin communication.

Next the researchers plan to put cameras on multiple penguins in a single group, to get a better view of dynamics in a single population.

"Information on their interactions may enable us to better understand penguin foraging behaviour and test our hypotheses regarding the evolutionary significance of group foraging in penguins," the authors conclude.

Gentoo penguin
An adult gentoo with its chick. Won Young Lee