The social system within the pack is based on the respect of rank. Largely due to the system of hierarchy within the pack, dogs are able to communicate effectively with each other by the use of three principal means of communication: voice, body and olfactory.
Barking: This characteristic sound produced by dogs is used both as a warning of danger and as an attention getter when the dog wants to express things like: happiness, frustration, anger, hunger etc…
Howling: Though most domestic dogs rarely howl, wolves on the other hand howl for a number of different reasons. They howl to keep in contact with the other members of their pack, to let other wolves know where they are, to get the pack together (for example, to chase off predators), ward off intruders into their territory and coordinate the pack’s maneuvers while hunting.
The rare occasions when a domestic dog will howl are usually the result of the dog being left alone for long periods of time or when the male dog is attracted to a female in heat. Dogs will often begin howling in response to the howls of other dogs, a behavior very similar to that of their wolf ancestors.
Short howl: This form of communication is often used to call attention to the dog. It is used when the dog is feeling poorly, uneasy or intimidated. Also used to ask for something needed or desired. Puppies often use this form of communication and it could in some aspects be compared to a young child’s crying.
Whining: Normally an indicator of pain, either physical or emotional, and on occasion fear. It is very common for puppies to whine and is often a defense mechanism when they are faced with a potentially dangerous situation.
Dogs also whine to demonstrate submission.
Growling: Most often used in a threatening way, dogs growl to show that they are not happy with or comfortable with what is in close proximity to them. It is a warning that if not heeded will often lead to the dog taking some form of physical action.