Before they left, the researchers tagged four birds with satellite tags and “water switches” that allowed them to track how far the animals traveled and how often they entered the sea. The data confirmed that the penguins continued to take moonlight swims throughout the breeding season. The researchers believe the males ceased their hunting activity once the females laid their eggs.
The findings, published in the Journal of Experimental Biology, suggest that previous research on emperor penguins was focused on too small a population to be taken as representative for the entire species, Dr. Kooyman said.
“Almost all the studies about winter breeding have been conducted from the research station Dumont D’Urville, which is about 100 meters away from a colony,” he said. That colony, which was prominently featured in “March of the Penguins,” is also 100 kilometers from the ice edge, making it impossible for penguins that breed there to take breaks for fishing.
The colony that Dr. Kooyman observed was farther south than Dumont D’Urville, and was located only about 10 kilometers from the ice edge. Thus the authors suggest that the length of a fast depends largely on the breeding colony’s proximity to water. The male emperor penguins in Cape Washington probably fast for about 65 days, they estimated.
Additionally, the discovery that penguins — who are believed to be visual hunters — can successfully hunt in the dark may be good news for a species that is contending with loss of habitat because of a warming planet. Researchers have expressed concern that the loss of stable ice in Antarctica could make it difficult for the animal to perform their breeding ritual.
“If there’s global warming, the bird has the resilience to go south, where they will continue to have stable sea ice for breeding that they would not have in the northern colonies,” said Dr. Kooyman.
As for why the researchers waited 20 years to publish their findings, Dr. Kooyman said he had hoped to return to Cape Washington to conduct a more detailed study.
“I think that emphasizes the difficulty of observing what we did,” he said. “But after 20 years I said, ‘Well, I think it’s time to write something about it.’”