Though separated by millions of years of evolution, penguins and dolphins use the same spectacular swimming style when they most need it – porpoising. It’s a dramatic mode of travel that involves rhythmic, rapid jumps (their entire bodies becoming airborne) alternating with high-speed underwater swimming. It’s named after one of the dolphin’s closest relatives, the porpoise. It’s also used occasionally by orcas and seals.
Penguins porpoise when they’re fleeing from a predator. They also accelerate and porpoise just as they’re leaving their colonies on a feeding mission, and when they’re approaching their colonies on the return journey. These are the critical times when a hungry leopard seal is likely to be submerged in the shallows, waiting to ambush and eat the slowest swimmers.
In Antarctica I also saw gentoo penguins porpoising to keep-up with humpback whales that were manoeuvring between swarms of krill. The penguins were travelling fast to stay close to the whales so they could eat the leftover krill that escaped the humpbacks’ bubble-net feeding.
As I observed, penguins can swim amazingly fast underwater. So, what’s the reason for porpoising? Perhaps the moment when a penguin is airborne might give it a visual update on the location of a pursuing predator or the humpback it’s following.
But porpoising’s primary benefit appears to be the critical boost it gives to breathing. A resting penguin breathes through its nostrils with its mouth closed. The nostrils are tiny openings on each side of the upper beak, little more than 1mm in diameter.
Air enters through the nostrils then passes through a maze of convoluted passages and chambers in which its temperature and water content are regulated to suit the penguin’s bodily needs in the dynamic environment of Antarctica. The air then continues its passage into the lungs. Though tiny and complex, the nostrils and nasal passages provide sufficient airflow to the lungs during times of low metabolic need, such as when a penguin is standing on the ice or incubating an egg.
But a penguin’s need for sustained, fast swimming – such as when it’s fleeing from a predator – puts enormous demands on its metabolism. At these times those tiny nostrils and convoluted nasal passages become a hindrance – they can’t deliver the necessary volumes of oxygen quickly enough for the animal’s hard-working muscles.
So, rather than slowing down to take a deep breath – which would be too risky for a penguin desperately trying to escape a pursuing leopard seal or orca – the fleeing penguin accelerates, leaps clear of the water, and opens its mouth. Oxygen-rich air flows directly and quickly into the trachea, bypassing the restrictions imposed by the nostrils and nasal passages, and from there moves straight into the lungs. Re-entering the water at the end of its leap and staying just below the surface, the penguin continues its rapid swimming, typically around 3m per second.
A porpoising penguin needs to be swimming fast enough to break through the barrier of the water’s surface and launch itself into the air. Scientists working in Antarctica using tiny data loggers taped or temporarily glued to the backs of penguins (and removed at the end of the observations) clocked them accelerating to around 10m per second just prior to porpoising.
Penguins can reach the high speeds needed to porpoise because their flippers, powered by huge chest muscles, act like powerful paddles that also bend and twist in ways unique among birds to generate the necessary forward thrust. They’re also helped by having a streamlined body covered by a continuous smooth coat of tiny interlocking feathers that water can’t penetrate, even under the pressures generated by porpoising and diving. Their bodies look to be as smooth as glass as they emerge from the water to porpoise.
While I was in the water in Antarctica marvelling at the adaptability of a penguin’s behaviour in response to the pressures of survival that led to porpoising, I couldn’t help imagining that a porpoising penguin looked like it was ‘smiling’, even though I knew it was anatomically impossible. On the other hand, some scientists who observed penguins porpoising at times when there was no obvious need have suggested they did it for the simple reason that they enjoyed it.
William Gladstone is a marine biologist and Emeritus Professor at the University of Technology Sydney’s School of Life Sciences with research and teaching interests in marine conservation biology, fish behavioural ecology, and marine environmental management.