Nice review / overview. Not my favorite Hitchcock, but it's characteristic of its era (which all of his films are).

Not many people know that Daphne du Maurier ripped off the concept from an early twentiteh century horror story by Arthur Machen, "The Terror," Unlike du Maurier's story (which I've read and enjoyed), "The Terror" does suggest an underlying cause for the revolt of nature: the brutality of humankind, specifically via World War I. The animals are essentially trying to correct the imbalance by eliminating the threat. Less horrific than the unexplained cause in the stories by Hitchcock / Hunter / du Maurier, but more devastating in its theme.