Researchers from the University of Manitoba have shown that birds can either be very good at flying or swimming, but not both. And they’ve been studying a very awkward seabird to prove it.
Animals that can fly really have it good. Flight allows for quick getaways, aerial view hunting, expanded territorial ranges, and the ability to travel vast distances when making seasonal migrations.
So, for a species to give up flight, there better be a damned good reason.
And indeed, the penguin did exactly such a thing about 70 million years ago, foregoing flight in favor of swimming. Scientists aren’t really sure why penguins made the switch, but they suspect it had something to do with a lack of land-based predators.
The High Cost of Flying
But a new theory, the biomechanical hypothesis, suggests that nature cannot provide a seabird with a wing that is proficient at both flying and swimming. For penguins, selectional pressures eventually tipped over in the direction of swimming, resulting in a vestigial wing that could propel the bird not through air, but through water. As a consequence, flight had to be completely abandoned lest the species remain mediocre at both — a condition that nature, with its preference for fitness peaks, will not endure.
For the rest of the story: http://io9.com/why-did-penguins-stop-flying-509052952