Learning to live in Antarctica
Tagging study reveals Emperor penguins’ first encounters with sea ice. Nick Carne reports.
New research shows just how well young Emperor penguins (Aptenodytes forsteri) cope when their parents quite literally throw them out into the cold at barely five months old.
They first – quite sensibly – head a fair way north of Antarctica to find some warmer open water in which to learn vital water skills. Only when they have deep-sea swimming and diving under control do they go back south to spend the winter making deeper dives within sea ice.
A paper published in the journal Marine Ecology Progress Series by US and French researchers also highlights the connection between juvenile diving behaviours and a layer of the ocean known as the thermocline, where warmer surface waters meet cooler deep waters below and where their prey likely gather in groups.
The findings provide insights into an important but poorly understood part of the penguin’s life cycle, which is “essential to being able to better predict the species' response to future climate change”, says lead author Sara Labrousse, from the Woods Hole Oceanographic Institution (WHOI) in the US.
Researchers from Centre d'Etudes Biologiques de Chize in France tagged 15 juvenile penguins just before they left their colony in Terre Adélie at the end of the year, when the weather usually starts to warm and the ice begins to break up, creating open waters near the nesting site.
The tags transmitted diving and location data via satellite. Three stopped working inside a month, for reasons that aren’t clear, but the remaining 12 continued, recording trips lasting from 86 to 344 days and more than 62,000 dives – the deepest to 264 metres.
Labrousse says the deeper dives likely were related to the depth of the thermocline and the seasonal change in the distribution of their prey, krill and other fish from the surface to the depths.
She and her colleagues discovered that, contrary to the belief that young penguins would avoid sea ice, they spend a great deal of their time there and dive in areas of high sea ice concentration, despite being inexperienced in these environments.
“The first trip at sea is critical for penguins, since food has to be acquired at a high rate to ensure that body condition and insulation are sufficient to allow survival and increased diving capabilities,” they write.
“Here we found that juvenile emperor penguins spent a significant amount of time foraging within sea ice, and exhibited seasonal differences in diving behaviour, likely in response to changes in prey distribution.”
Emperor penguins are the largest species of penguins. They are particularly vulnerable to climate change because their life cycles are so dependent on sea ice. Their breeding cycle begins in March (autumn in Antarctica) when the sea ice is thick enough to support their colony.
After laying a single egg each, the females leave the colony to catch fish and fatten up so they can feed their chicks. The males stay behind and cradle the egg on the tops of their feet, tucked under their brooding pouch for warmth and protection.
Too little sea ice during this time can reduce the availability of breeding sites and prey; too much means longer hunting trips for adults, which in turn means lower feeding rates for chicks.
"Juveniles stay at sea for five or six years before they return to the colony to mate," says Stephanie Jenouvrier, from WHOI. "We need to better understand the dynamics of what happens during the time the juveniles are away from the colony.
“Understanding how they will respond to the changing landscape in terms of breeding and other life history stages is key to predict population responses and species persistence to future climate change."