While exploring the Falkland Islands, Darwin was interested to observe the behavior of the upland goose. Like birds on the Galápagos Islands, this goose had no instinctive fear of humans, and a hunter could kill "more of the upland geese in one day than he can carry home." On the mainland, however, where it had been hunted for generations, Darwin noted that the same species was wary of hunters and avoided people. Clearly, a species could change over time in response to its environment, at least in its instinctive behavior.
The most extreme example of specialization Darwin saw in the Falklands was the Falkland Island steamer duck. Its beak is powerful enough to crush shellfish, its primary food, and its wings are used only as paddles. Darwin wrote,
"Their wings are too small and weak to allow of flight, but by their aid, partly swimming and partly flapping the surface of the water, they move very quickly. The manner is something like that by which the common house-duck escapes when pursued by a dog."