boundaries of a captive dog's territory will be visited frequently by intruders, thus triggering the bark response as a warning. Additionally, dogs densely populate urban areas, allowing more opportunity to meet new dogs and be social. For example, it is possible that kenneled dogs may have increased barking due to a desire to facilitate social behavior. Dogs' close relationship with humans also renders dogs reliant on humans, even for basic needs. Barking is a way to attract attention, and the behavior is continued by the positive response exhibited by the owners (e.g., if a dog barks to get food and the owner feeds it, the dog is being conditioned to continue said behavior). Types Barking in domestic dogs is a controversial topic. While barking is suggested to be "non-communicative," data suggests that it may well be a means of expression that became increasingly sophisticated during domestication. Due to the lack of consensus over whether or not dogs actually communicate using their barks, not much work has been done on categorizing the different types of barking in dogs. That which has been done has been criticized by Feddersen-Petersen as "lack[ing] objectivity." Using sonographic methods, Feddersen-Petersen identified several distinct types of barks, then analyzed them for meanings, functions, and emotions. He separated dog barks into subgroups based on said sonographic data: Not all breeds demonstrated every subgroup of barking. Instead, significant variance in vocalization was found between different breeds. Poodles showed the least of all barking sub units. Additionally, barking in wolves was observed as notably less diverse. For example, wolf barks are rarely harmonic, tending instead to be noisy. There is some evidence that humans can determine the suspected emotions of dogs while listening to barks emitted during specific situations. Humans scored the emotions of dogs performing these barks very similarly and in ways that made sense according to the situation at hand. In one example, when subjects were played a recording of a dog tied alone to a tree, a situation in which one could reasonably infer that the dog would be distressed, the human listeners tended to rank the bark as having a high level of despair. It has been suggested that this may be evidence for the idea that dog barks have evolved to be a form of communication with humans specifically, since humans can so readily determine a dog's needs by simply listening to their vocalizations. Further