Incomprehensible Animal Behaviour

[Khandro]

I'm looking for an analogy in the animal kingdom for something I'm writing. An action an animal does and seems to be important them, but remains incomprehensible to us.
I thought of beavers building dams with such determination, but I think there might be an un understandable purpose i.e. to catch fish - is that so?
Eels to the Sargasso, salmon fighting their way upstream etc. any suggestions please?

[wildwood]

brinjal - A good observation, but Weaver finches build a lot of extra nests so they have more chance of a hen finch finding one that is attractive to her. It also serves to lower the chance of a predator hitting the nest with eggs/chicks.