Emperor penguin foraging behaviour under investigation

New Zealand marine ecologist Dr Kim Goetz and her collaborators at the National Institute of Water and Atmosphere (NIWA) have made some surprising discoveries about the previously unknown diving and long-distance swimming abilities of emperor penguins outside the breeding season.
Emperor penguins are found only in Antarctica and are the tallest and heaviest penguins growing up to 122cm high and weighing in at between 22 and 45kg.

Dr Goetz’s recent project tagged 20 emperor penguins in 2013 and analysed data on their movements transmitted via satellite. She discovered the penguins travelled between 273km and nearly 9000km and completed dives of between one and 32.2 mins exceeding their previous recorded dive record of 27.6 minutes.

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

To the researcher’s surprise some adult emperor penguins had stayed at Cape Colbeck after most had left and their transmitted data about their foraging behaviour revealed these penguins were not breeding birds.

“If they were breeders 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,” Dr Goetz said.

This gave Dr Goetz and her team the opportunity to gather a lot of information about a demographic group that they hadn’t intended to study.

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.
Initially the penguins, which are thought to be visual predators, travelled a short distance 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,” Dr 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. “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.

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

“The study showed the animals go far further than we thought and this has a number of implications for their survival. 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.