How do beavers learn how to build dams?
Question summary: is dam building learned or instinctive in beavers?
A blog post from 2011 references an article in the Juneau Empire titled Running water is sound of spring for beavers.  This article is no longer hosted on the Juneau Empire website, but archived versions are available.
Here's an excerpt (emphasis mine) --

Swedish biologist Lars Wilsson spent years studying captive and wild beavers, and he gained remarkable insights into their behavior. He raised beavers in an outdoor enclosure and in a large indoor terrarium ...
Wilsson initially captured four adult beavers and later he raised a number of beavers from infancy, some in small colonies with their parents and some completely isolated from adult beavers. He isolated the young beavers to see what beavers learn from their parents and what behaviors are instinctive.
He found that young beavers - who had never even seen a beaver dam - were able to build almost-perfect dams at the first opportunity.
The foundation of sticks and logs anchored to the stream bottom, the interwoven lattice of trimmed branches, the mud chinking, every aspect of dam building was hard-wired. Beavers do get more skilled at dam building as they gain experience, but the building behavior is instinctive.
Wilsson learned that the sound of running water is the cue for dam building and dam repair. In one experiment, he played a recording of running water, and the young beavers built a dam in a tank of still water in the terrarium. In another peculiar experiment, his captive beavers built a &quot;dam&quot; on a concrete floor against a loudspeaker that played the sound of running water.