Rusty and I were coming in from an evening bathroom break when a dog in our building started barking. Immediately, Rusty stopped and turned his head to listen in...I wondered what they were talking about or what Rusty was hearing. 

Dogs have evolved a complex set of vocalizations, body language, and chemical signals to convey different messages to other dogs. Here are some of the main ways dogs communicate with each other:

Barking - Different barks can mean different things. Short sharp barks are often used as alarms or warnings, while a string of solitary barks is usually an indication of loneliness or boredom. Howling is a long, mournful sound dogs make to communicate over longer distances.

Body language - Dogs rely heavily on body language to express emotions and intentions. Raised hackles, tense posture, growling with bared teeth are signs of aggression, while a relaxed open mouth and wagging tail are friendly gestures. Submissive signs include crouching low, rolling on the back, and tucking the tail.

Scent marking - Dogs have a powerful sense of smell and leave urine and feces in strategic locations to relay information. They can detect scents that reveal identity, sex, and even health status of other dogs.

Vocal tones - Dogs don't just rely on the meanings of different barks, but also vocal tones. A high-pitched yip is usually an expression of happiness and excitement. Low-pitched growls are warnings. Whines can indicate anxiety or distress.

Facial expressions - Dogs communicate a lot through their facial expressions. Ears pricked forward or relaxed, tension or looseness around eyes and muzzle, reveal how they are feeling. A dog will avert its gaze in submission.

Tail wagging - How fast a dog wags its tail and the height reveal its emotional state. Broad vigorous wagging is friendly, while a low tentative wag can mean uncertainty. No tail wag at all indicates aggression.

Dogs are highly adept at understanding messages from other dogs using this complex interplay of vocal, visual and chemical signals. From puppyhood, they learn the nuances of canine communication which forms the basis for developing relationships in their pack. While humans use words, dogs use a sophisticated system of non-verbal communication. Paying attention to how our dogs communicate gives us insights into their emotions and state of mind.