Where in world did you come up with duck? One doesn't
tape ducks; one tapes ducts. Except it isn't very good for that...

So why the latter?

It might originally have been called duck tape. See the Etymology section of
the Wikipedia article.

http://en.wikipedia.org/wiki/Duct_tape

The issue is confusing, because it wasn't used for ducts until long after it
was invented.