Dogs have an olfactory sense 40 times more sensitive than a human’s and they commence their lives operating almost exclusively on smell and touch. The special scents that dogs use for communication are called pheromones. Different hormones are secreted when a dog is angry, fearful or confident, and some chemical signatures identify the sex and age of the dog, and if a female is in the estrus cycle, pregnant or recently given birth. Many of the pheromone chemicals can be found dissolved in a dog’s urine, and sniffing where another dog has urinated gives the dog a great deal of information about that dog. Male dogs prefer to mark vertical surfaces and having the scent higher allows the air to carry it farther. The height of the marking tells other dogs about the size of the dog, as among canines size is an important factor in dominance.
Dogs (and wolves) mark their territories with urine and their stools. The anal gland of canines give a particular signature to fecal deposits and identifies the marker as well as the place where the dung is left. Dogs are very particular about these landmarks, and engage in what is to humans a meaningless and complex ritual before defecating. Most dogs start with a careful bout of sniffing of a location, perhaps to erect an exact line or boundary between their territory and another dog’s territory. This behavior may also involve a small degree of elevation, such as a rock or fallen branch, to aid scent dispersal. Scratching the ground after defecating is a visual sign pointing to the scent marking. The freshness of the scent gives visitors some idea of the current status of a piece of territory and if it is used frequently. Regions under dispute, or used by different animals at different times, may lead to marking battles with every scent marked-over by a new competitor.
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