Penguin wings help them turn underwater

Abstract

As one of the most charismatic birds around, penguins are famous for being unable to fly. But just because these birds can't fly, doesn't mean that they don't use their wings to move. Penguins swim by using their wings as if they were flying, flapping them to glide gracefully through the water in search of food. Perhaps even more importantly, penguins are able to make some remarkably acrobatic underwater manoeuvres in order to escape predators or catch particularly agile prey. However, not much is known about how penguins perform simple movements, such as turning, while they swim. This led Natsuki Harada and Hiroto Tanaka of the Tokyo Institute of Technology, Japan, to ask the question: what are the penguin's wings doing while they turn underwater? So Harada and Tanaka headed to the Nagasaki Penguin Aquarium in Nagasaki, Japan, in March 2018 and again in September 2019 to film some gentoo penguins (Pygoscelis papua) as they swam through the water of their enclosure. As the birds manoeuvred around, the duo was particularly interested in how they were using their wings to perform turns. When gentoo penguins turn, they do so with their belly facing the inside of the turn. This is different from flying birds and even airplanes, which turn with their bellies facing the outside of the turn. While swimming, the penguins also perform two different types of turns: gliding turns where the wings are held out to the side, but don't flap, and powered turns in which the wings do flap. Because the penguin's wings are acting not only as rudders, but also as a means of propelling themselves forwards, the researchers focused their attention on powered turns.During a powered turn, penguins use the upward flapping motion to help them turn while using their downward flap to move forwards. This is particularly surprising because when penguins swim straight forward, the upwards flap generates slightly more of the power to move forwards than the downwards flap. Not only are the penguins changing how they move forwards, but these aquatic birds are also changing the timing of their flaps. When swimming in a straight line, the left and right wing would be in sync. However, when the penguins turn, the wing on the inside of the turn flaps earlier than the wing on the outside of the turn. The videos also showed that the penguins are rotating their inside wing, which makes them turn. The combination of all these movements also makes the penguins generate centripetal force, helping to speed the animals through their turn.So just how manoeuvrable are the penguins? Harada and Tanaka noted that without motivation from a predator chasing them or food to catch, the penguins were able to complete a turn in less than 1 body length, about 0.5 m. When the researchers compared the penguin's turns with those of other marine animals, the birds fell right in the middle, neither extremely manoeuvrable nor unwieldy. Harada states, ‘our measurements captured gentler turns than the other studies', suggesting that adding an incentive such as food may increase their manoeuvrability. The duo is also quick to point out that the wings are not the only body part that the penguins use to help them turn; the feet, body, head and tail probably play a role in their manoeuvrability as well. So penguins are certainly using their wings to gracefully move about under the water while escaping dangerous leopard seals and catching delicious fish, even without the ability to take to the skies.