Unlike ducks and swans, which take their young to the water and show them how to forage, penguin parents simply abandon their chicks when they are about five months old. The fledglings become very hungry and eventually leave the colony to find open water. When they do, they have to learn quickly what and how to hunt.
For many years researchers have wondered where juvenile emperor penguins go once they reach the ocean. Do they stay near the colonies, or do they find a good foraging area and stay there? Now that instruments, such as satellite trackers, are small enough to be deployed on young penguins, we can follow them on their first trip to sea and find answers to these questions.
In December 2006 we deployed 10 satellite trackers on fledgling emperor penguins at the colony at Auster, about 54km east of Mawson station. The colony, which comprises around 11–12,000 breeding pairs, had split into six different ‘suburbs’ that were up to 1.5km apart.
When choosing our ‘volunteers’ we wanted the fattest ones because they had the best chance of survival. We also needed fledglings with proper adult feathers, not down, so that the satellite trackers would remain in place once glued to their back.
Before deploying the satellite trackers we weighed each fledgling to ensure it was fat enough. On average, our volunteers weighed nearly 16kg; the satellite trackers only weighed 92g and were powered by two AA batteries. To conserve power the trackers were programmed to transmit data only four hours in 48.
Upon departing the colony the fledglings had to cross nearly 50km of fast-ice and could not feed for several days until they reached open water. Ten youngsters stayed in the colony for three to eight days after we left. Most of them then started to head north towards the ice edge. One of the young birds walked towards the continent for nearly two days before it realized that it was going the wrong way. It turned around, went back to the colony and then followed the others.
Once they reached the edge of the fast-ice the young emperor penguins had 200–300 km of pack-ice in front of them. It was remarkable to see how they moved through it, heading directly north for the deep oceanic waters of the Southern Ocean. Some of them spent a considerable time north of 60°S. For example, Fledgling 2 was tracked for 166 days and spent 76 of those north of 60°S.
The fledglings dispersed over nearly a quarter of the Southern Ocean in their first six months at sea. The eastern-most position was at 93°E and the most westerly position reached was at 7°E – over 2300km from their birth colony! The total distance traveled by one individual was nearly 7000km.
But the story doesn’t end here. Emperor penguins are three years of age, or older, when they first return to their colony to breed. Our research has given us a glimpse into their whereabouts for the first six months after leaving the colony. We still need to find out where they spend the other two and a half years. To do that we need to repeat the tracking studies at Auster and adjust the transmission time of the satellite trackers so that we will be able to follow the young penguins for much longer than six months. Over the coming years we also plan to go to other colonies and examine what young emperor penguins do in other parts of Antarctica.
Southern Ocean Ecosystems program, AAD