That's pretty strange. I mean, an echo is merely sound reverberating off of distant surfaces, so why wouldn't a duck's quack echo? I'd assume it's loud enough. Maybe it's just because there aren't any ducks living in the mountains.
Maybe I'm giving more thought to this topic than is necessary.
my guess is it has something to do with the pitch involved in the quacking sound. as funny as that sounds...ya know i bet myriads duck of smugness knows. 😀