Emperor penguin behaviour not black and white

Niwa's Dr Kim Goetz with emperor penguins in Antarctica. Photo / Rod Dunbar

Scientists have made some unexpected discoveries about the frozen continent's best-known residents: the emperor penguin.

Found only in Antarctica, they're also the tallest and heaviest penguin species on Earth, growing up to 122cm high, and weighing between 22 and 45kg.

Five years ago, Niwa scientist Dr Kim Goetz's research tagged of them and remotely observed them travelling between 273km and nearly 9000km, while completing dives that ranged up to a record-breaking 32.2 minutes.

But it was finding the penguins in the first place that was most intriguing.

"Our original goal was to tag breeding penguins at Cape Colbeck after their annual moult at the end of January. But because the voyage was delayed we didn't get there until early March," Goetz said.

"We didn't expect penguins to still be there and thought we would have to locate them on the pack ice which was going to be more difficult."

To their surprise, some adult emperor penguins had stayed at Cape Colbeck, and were quickly tagged.

When they did eventually leave, the transmitted data revealed that these penguins were not breeding birds.

"If they were breeders, their tracks would have been a lot shorter and they would have returned to the breeding ground by early June but they didn't.

"They kept foraging because they had no reason to go back."

This gave Goetz and her team the opportunity to gather a lot of information about a demographic group that they hadn't intended to study, at a time when the birds experience the most severe environmental conditions of the annual life cycle.

"It's really cool information because it shows just how far-ranging they are."

Little is known about emperor penguin behaviour after adult birds leave the breeding colonies in mid-December to mid-January to prepare for the moult.

During the moult they must remain out of the water while they replace all their feathers.

As a result, the birds travel east where sea ice is more reliable, providing a secure resting platform.

Initially, the penguins, who are thought to be visual predators, travelled a short distance to the Bay of Whales, where researchers think they were feeding on Antarctic krill on the Ross Shelf.

Then they headed into deeper waters.

"What we found is that there were distinct differences in the way the penguins dive depending on the depth of the water they are foraging in," Goetz said.

On the Antarctic continental shelf, the dives were shorter and shallower, while further out to sea the penguins dove deeper and for longer periods of time.

Found only in Antarctica, emperors are the tallest and heaviest penguin species on Earth, growing up to 122cm high, and weighing between 22 and 45kg. Photo / Kim Goetz

"This is probably related to diet. On the shelf, the shorter dives suggest they are foraging for krill, while in the deeper ocean it is likely to be fish."

On average, penguins dove 90.2m but did occasionally dive as deep as 450m.

More than 96,000 dives were recorded and most tags remaining attached for at least six months.

Goetz said further research is needed to determine whether this behaviour is normal or a result of changing sea ice conditions.

In addition, future research should focus on linking prey species to emperor penguin behaviour.

"This study showed that animals go far further than we thought – this has a number of different implications for their survival," she said.

"That's why understanding their entire life cycle, especially when birds are not restrained by chick-rearing duties, is critical to predicting how emperor penguins might respond to environmental changes."

Goetz is due to return to the ice later this year as part of a multi-disciplinary project that includes tracking the movement of emperor penguins and Weddell seals.