That missing piece of information has now been found. Researchers with Japan's National Institute of Polar Research electronically tagged 175 penguins with Global Positioning System devices, accelerometers and video cameras across four seasons with different sea-ice conditions, allowing them to track penguins on their trips, categorize walking, swimming and resting behavior, and estimate the number of prey captured during dives.
Watanabe explained that in ice-free conditions, penguins are able travel more by swimming than by walking.
This higher foraging success led chicks to grow faster and higher body mass in adult males and females.
"This may seem counter-intuitive, but the underlying mechanism is actually quite simple", said Yuuki Watanabe, lead author of the study, in a news release.
The latest findings don't hold for all of Antarctica, and in future studies, researchers hope to explore the effects of sea ice extent on different penguin species living in different parts of the continent.
Researchers tracked penguins "in four seasons with contrasting sea-ice conditions".
"In the ice-covered seasons, penguins traveled slowly by walking and needed to find cracks in the ice, where they dived repeatedly", Watanabe said.
This contrasts with its polar twin, the Arctic, which has suffered through a marked decrease.
But this is not expected to last much longer as the climate changes, with Antarctica also projected to see a decline in its sea ice.
New research as found that Adelie Penguins greatly prefer reduced sea ice conditions, making it a rare victor from the effects of climatic warming in Antarctica.
Previous studies that made mention of the relationship between population growth and sea-ice have only ever established a correlation, not a cause.
To learn more, personnel at the National Institute of Polar Research set off to the Antarctic over the course of four breeding seasons during the past decade - 2010 to 2011, 2011 to 2012, 2012 to 2013 and 2016 to 2017.
The team electronically tagged 175 penguins with Global Positioning System devices, video cameras and accelerometers - which are used to measure acceleration.
During that winter, a large quantity of sea ice in the bay broke up and drifted away with currents, providing a natural experiment by which the scientists could observe penguins foraging in the absence of sea ice.
In seasons with heavy sea ice, the penguins have to walka long way to find cracks in the ice in order to access the waters where they hunt, taking sometimes quite lengthy rests along the way.
But when there is less sea ice, penguins can dive anywhere they want, often just entering the water right by their nests.
Not only is this fortunate arrangement more energy- and time-efficient for the penguins, but it expands their foraging range. Most importantly, this likely reduces competition with other penguins for prey and allows them to catch more krill-the penguin's main prey.
What's more, less ice means more sunlight reaches the water, leading to blooms of plankton that krill feed on, thus supplying penguins with more food.
That saved energy was put into growth and reproduction and ultimately provided a big boost to populations.
However, all this only happens for those penguins that live on the main, "continental" section of Antarctica.
The researchers have a few hypotheses as to why this might be the case, but further research is now required.