Like human beings, animals uses their senses to determine friend or foe and communicate using body language and verbal intonations. My Scottish Terrier, MacGregor is a good communicator with other animals and people. In a matter of minutes, he uses his eyes, ears and nose as his cue to engage in play or walk away from another dog. The alpha dog is dominant in short order, with body language of followers connotating submission, by avoiding eye contact, waiting on cues from the boss and rolling on their back. When MacGregor cued a neighbor's rescue pitbull he wanted to play, he waited for body language signals. If the pitbull approached in a playful manner, they joined in friendly interaction. When MacGregor felt threatened by over-exuberance, he stands like a statue, virtually shutting down the action without being aggressive. It is an interesting, telltale dance that illlustrates an instinctual language among canines.
When MacGregor interacts with me, it is a combination of instinct and learned adaptive behavior that speaks to me. He has learned my patterns and has devised a way of letting me know without making a sound that he needs to go outside. At precisely 4 p.m. his behavior reminds me it is his dinner time. He uses different vocalizations for different emotions or needs. He uses a high-pitched, clipped bark when one of his toys has escaped beneath the couch or a corner that he cannot access. Outside he barks and then waits for reciprocity from another, unseen, barking dog. If he sees someone from the apartment building that he recognizes, he wags his tail and trots up to them. If they do not acknowledge him, he barks in an excited, demanding way, usually with the neighbor turning around to pet him.
Last summer the credit union across the street was robbed and we were outside walking when the offender left the rear exit of the credit union on foot. Mac sensed something wrong and would not desist his animated barking and growling, until the man boarded a bus. I realized, after the fact, while watching the news and seeing a photo of the man that we had seen the bank robber. I would not have noticed him, but for MacGregor's strong reaction.
Animals have innate sensory abilities that give them advantages in communicating that are built-in to use for survival and protecting those they love.