In the 1960s, Swedish biologist Lars Wilsson wanted to know if this industrious behavior was learned or innate. He decided to capture four adult beavers with the intention of raising them in different habitats and chose a few of them to raise in isolation in order to study which of their behaviors were instinctual. When released into running water, the young beavers built near-perfect examples of dams on their first try. Instead, when placed in still or very slow-moving water they made no attempts to build. But when Wilsson played them the sounds of running water through a speaker, their instincts kicked in. Suddenly the beavers were compelled to start building over the speaker, convinced that it was the source of the leak.

Source: Mental Floss