What are dogs communicating when they bark?

Dogs bark to communicate with other dogs and persons. It does not have a meaning like the words of the human language, but it represents a type of communication that reports the emotional state of the dog who is barking.
We are talking about the bark, one of the key features of dogs. Their ancestors, the wolves, do not bark as much as dogs, and it is probable that domestication had much to do with the greater tendency of the latter to bark.

Dogs can bark in many situations: when somebody approaches or enters their territory, to greet, to receive attention, to threaten and to defend themselves, when playing, when they are alone or in pain, in conflict, frustration or excitement, in answer to the barks of other dogs and even in situations where it is not possible to identify any triggering stimulus.

Due to its presence in so many contexts, it was originally thought that barking did not have a specific sense and that its function was simply that of drawing attention. Now it has been discovered that the acoustic characteristics of a bark are consistent according to the context: barks when playing and when in isolation, for example, are usually acute, whereas barks when a stranger rings the doorbell is usually severe, longer and with smaller intervals between each bark.

Dogs and people (including children of 5 years of age) are able to detect these differences. One study has shown that people can associate the recording of a bark to the context in which it has been emitted in the correct way, but the capacity depends on the situation. There are more successes with barks emitted in response to a stranger, during training for defence or when the dog is left alone. However, recognition is less precise when it is a dog that barks when it watches a ball, before leaving to take a walk or while playing.

When the sense of barking is interpreted, it is important to consider the size of the animal, because there is a close relationship between the length of the vocal system, the size of the dog and the features of the bark. In fact, the barks of a small-sized dog are always more acute than those of a large dog, regardless of the context of their emission.

It is not known whether dogs intentionally modify the characteristics of their bark to communicate a message to dogs and people, but it is clear that analysing some aspects of the bark can be helpful to obtain data on the emotional state of dogs, information that can be particularly useful in the diagnosis of problems of excessive vocalisation.