Have you also wondered why dogs bark? Some dogs bark more than others, and they bark for various reasons. Causes for a dog to bark can include alerting you to a stranger or threat in the dog’s territory, distress, frustration, irritability, separation distress, anxiety, boredom and insecurity, to name only a few.
For the owner, it is quite acceptable when a dog barks at an intruder or at other intruding animals, but it becomes a big problem when the dog reverts to excessive barking, apparently for no reason, becoming an irritant to his owner and the neighbours. However, it must be strongly noted that there is ALWAYS a reason why a dog barks excessively and it is not because the dog wants to irritate humans or is being a naughty dog!
Some breeds of dog inherently have a more vocalised disposition than others; that is what they were bred for, thus the behaviour is contained in their DNA. It is essential to always do research on the breed that you are interested in, as this will give you an idea of the barking behaviour you can expect.
Anlé Allison, behaviourist

