Penguins can fly? The title of this article is sure to elicit raised eyebrows and deep furrows of confusion, but it is true — penguins do, in fact, fly.

But, they fly underwater. Penguin flippers evolved in order to “fly” underwater, employing similar mechanisms of flight that birds use. Penguin wings are modified as paddles that can provide propulsion speeds of 30 kilometres per hour. They are effectively tapering wings (just like an airplane’s). Also, quite remarkably, penguin wings are able to generate forward thrust on both the up and down stroke cycles, by changing their orientation, in which case the pitch of the wing is raised on the upstroke but lowered on the downstroke. In addition to this hydrofoil-like feature, penguins also use their webbed feet, which are effectively rudders that trail behind in the water and steer in a directed fashion.

Here is a video, showing penguins swimming underwater. They are, technically, flying, but in a different medium.

The fact that the locomotion medium for penguin is primarily water required that penguins evolve several adaptations. Firstly, because water is denser and heavier than air, penguin bones are not hollow as they are in birds. They are solid and as such, they help penguins sink down more easily in water, which is more economical of energy. The bones of the wing are also fused together, giving rise to this rigidly strong paddle-like flipper which penguins possess, where the joints of the elbow and wrist are fixed. This means that penguin wings cannot fold and shoulders provide the only mobility. The bones that form the wing are also flat and narrow so as to adopt a paddle-like structure.

Penguins also possess a long streamlined, torpedo-shaped body, which provides less drag and ultimately economises on energy costs during locomotion since this reduces the power required for propulsion. Penguin bodies are therefore disproportionately bigger than their wings. Since flight feathers would become waterlogged in water, their functionality became very much reduced during the course of penguin evolution. Penguins, today, only possess mere vestigial scale-like feather structures, which serve only to reduce drag.

However, the evolution of the paddle-like stiff flippers in penguins also required increased muscle mass, especially since it provides froward thrust during both the up and down strokes. Accordingly, penguins have highly developed pectoral muscles. In particular, the pectoralis and the supracoracoideus power wing flight movements. The pectoralis muscle is the largest penguin muscle and it serves to depress wings and acts as the downstroke muscle. The supracoracoideus muscle is also massively developed in penguins. It elevates the wing and powers the upstroke.

So, the next time you want to win a bet. Yes, penguins do fly – albeit in a different medium, water. They adjusted the functionality of their wings in order to account for living in water.

Bibliography

Storer, R. W. 1960. Evolution in the diving birds. Proc. 12th Int. Ornithol. Congr.: 694-707.