how seabirds catch food | 177‘exploding’ out of the sea to jump a metre or more onto the security of
ice beyond the jaws of a Leopard Seal. To facilitate a clear run at an
isolated exit hole through ice, Emperor Penguins that have been feeding
at the undersurface of ice descend to depth before returning to the exit
hole.^30 Of course, sometimes the Penguins are embarrassed by a failure
to achieve the necessary height and, amid whirring flippers, splash back
shamefacedly into the water. In a study of nine instrumented penguins,
the maximum swim speed in the second before exit correlated with the
above- water height of the ice surface, indicating that the penguins an-
ticipated the ice height. Nevertheless there were 37 failures among 386
leaps. Those failing penguins did not seek out lower holes after failing
to exit through the higher holes. Rather, swim speed, typically around
3 metres a second, was increased for subsequent attempts. And the re-
searchers, watching their subjects from a sub- ice observation chamber,
could see that some exits were achieved with little or no flipper beating;
the positive buoyancy generated adequate speed.^31
As a submerged penguin approaches the surface, air trapped within its
plumage and lungs expands, increasing the bird’s buoyancy and rate of ascent.
This impetus helps Gentoo Penguins, and other species, leap onto ice.