— Seabirds like these penguins at Cape Washington, Antarctica, flap their wings faster underwater than swimming birds that can also fly, like guillemots (Image: Katsufumi Sato)
Marine animals may trade off their swimming efficiency against flying ability, according to a novel study in which motion sensors were attached to wild seabirds, whales and penguins to reveal how they move underwater.
Biologists know that small animals move their legs, wings or fins faster than large animals when running, flying or swimming. For example, a bee flaps its wings faster than a seagull, at an impressive 230 times per second. See them both in action, here (1.7 MB, mov format requires the latest version of Quicktime).
Until recently, it has been difficult to find out if this rule applies in the ocean. Captive animals do not move in the same way as those in the wild, researchers have shown.
So Katsufumi Sato at the University of Tokyo, and colleagues, attached accelerometers to a variety of wild swimming animals, including penguins, flying seabirds and killer whales. See an accelerometer attached to a child in this movie (4.3 MB, mov format), which opens with waddling penguins.
Satos team found that the size-to-flap ratio does not apply to seabirds. Guillemots and razorbills use their wings for both flying and swimming, and underwater they stroke at a lower frequency than other seabirds of a similar size, such as penguins, suggesting inefficiency for their size.
Some biologists believe that all animals have evolved to move their legs, fins or wings using as little energy possible, but this study shows that some marine animals trade off their swimming efficiency against flying ability, the researchers say.
Journal reference: Proceedings of the Royal Society B (DOI: 10.1098/rspb.2006.0005)