The Estrela Mountain Dog is a Livestock Guardian Dog with a rich history originating in the Estrela Mountains of Portugal.  They were bred for the purpose of livestock protection from predators.  Their guarding stems from their bonds with their humans or animals and is instinctual.   The mere presence of an Estrela is typically enough to ward off predators, but they will endeavor to intimidate a predator if necessary by barking and showing aggression.