By Paul Rincon
BBC News Online science staff
Scientists have obtained amazing images of penguins interacting with each other underwater by strapping miniature cameras to the flightless birds' backs.
The penguin cameras weighed only about 73g (Image: Royal Society)
Observing genuine underwater behaviour in marine birds and mammals is tricky because the presence of a diver nearby can make the animals act unnaturally.
By attaching cameras to the penguins, the scientists could see that the birds kept together during dives for food.
Details of the work appear in the Royal Society journal Biology Letters.
"What's quite nice about the camera is that it's small enough that it has virtually no impact on the animals themselves," co-author Dr Phil Trathan, of the British Antarctic Survey (Bas), told BBC News Online.
"If you're photographing diving penguins using a diver or a remote camera or something, you often influence their behaviour yourself."
The birds may forage together to avoid predators (Image: Royal Society)
The researchers, from Bas and the National Institute of Polar Research, Tokyo, Japan, attached cameras to five chinstrap penguins (Pygoscelis antarctica) and five Adelie penguins (Pygoscelis adeliae) from colonies on Signy Island, Antarctica.
They found that the penguins swim closely with at least one other bird on about 24% of foraging dives, in which they target the tiny shrimp-like Antarctic krill (Euphausia superba) for food.
The researchers propose that because the cameras only look forward, it suggests the animals may swim in a group for about half of their foraging dives.
The scientists think the co-ordinated behaviour may be a strategy for avoiding predators rather than to corral the krill.
Birds may accompany each other for half their dives (Image: Royal Society)
"Everything we do with wild animals has an impact," said Dr Yves Cherel of the Centre d'Etudes Biologiques de Chize in Villiers en Bois, France.
"Even putting devices on the backs of penguins can change their hydrodynamic shape underwater. But about 15 years ago, we knew virtually nothing of the diving behaviour of marine mammals. It's always a trade off."
In future, the scientists hope to improve the resolution of the cameras and use the technique to observe how the penguins target the krill. This information could have conservation value for the penguins.
"We hope to look at the densities of the krill that the penguins are exploiting," Dr Trathan explained.
"That will give us information that we can then use in the management of fisheries to see where there is potential overlap in the sorts of densities that the fishermen go for compared with the densities the penguins go for."