Why Do Dogs Mark Their Territory?
The simplest answer is they don't.
In The Intelligence of Dogs, author Stanley Coren gives us the classical explanation of this myth: "All canids use urine ... to mark the limits of their territories. In males this marking behavior is usually accompanied by leg lifting to direct the urine against large objects (trees, rocks, bushes) to place the scent at nose height for other dogs and to allow the scent to radiate over a large area. Some African wild dogs ... scrabble as high up the trunk of a tree as possible before squirting their message."
First of all, dogs urinate far beyond the boundaries or limits of their so-called territory. Secondly, males aren't the only ones who lift their legs; some females (usually the anxious type) do this as well. Thirdly, dogs don't just urinate on large objects, but on vertical objects (trees, posts), unfamiliar or inorganic objects (tires, plastic bags, fire hydrants), and on anything carrying a scent that the dog wants to cover (such as another animal's urine or feces).
Coren is not responsible for the myth. His offhand re-telling of it, as if it were a scientific certainty, merely highlights a general tendency in science: in attempting to dissect how an animal's behavior might serve an adaptive purpose -- in this case marking would be a hypothetical means of limiting competition within a niche or habitat -- most scientists blur the line between what makes sense in terms of the grand arc of evolution, and what an individual animal is capable of in terms of its cognitive abilities.
Of course if a biologist who witnessed the African wild dogs madly scrabbling up the tree trunks did so with the belief that dogs urinate to send a message to other dogs, their behavior would, no doubt, confirm his hypothesis. But if we approach this behavior with a clearer mind we might ask, how could these dogs possibly know the "nose height" of another, purely hypothetical dog who might (or might not) come along at some undetermined point in the future?
In The Secret Life of Dogs, anthropologist Elizabeth Marshall Thomas compares a dog's urine marks to Hansel and Gretel's trail of pebbles and bread crumbs: a means of finding their way home. But that would mean the dog was planning for the potential (thus, hypothetical) possibility of getting lost. I've never seen any evidence for that kind of thinking in the dogs I've known. They live totally in the now moment.
Roger Caras, whose voice used to be heard each year at the Westminster Kennel Club Dog Show in New York, was fond of saying that when a dog sniffs a fire hydrant he's "reading his mail". This is highly anthropomorphic, yet it's hard to dispute that a dog does get information from the scent of other dogs this way. The only question is, did the dog who left the scent do so with the intention of "sending a message" to the one who comes along later?
It doesn't make sense that any dog would have the intelligence necessary to leave messages for other dogs in this manner because in order to do so he would have to be capable of propositional and/or hypothetical thinking, directed fantasy, mental time travel, not to mention a full-blown theory of mind. "If I mark this fence (propositional thinking), Spike will come along some time in the future (directed fantasy, hypothetical thinking, mental time travel), sniff it (more fantasy, more hypothetical thinking), and know he's in my territory (theory of mind, abstract and conceptual thinking) and start to feel nervous about being here (more theory of mind)." That's pretty complicated thinking for a dog.
Territory is defined by biologists as an area which an animal will defend against intruders of the same species. But how is such an area delineated in the animal's mind? Are its boundaries visible and concrete or imaginary and abstract? Is a dog capable of forming a mental image of where his territory begins and ends? And if animals have no sense of self and other, how could they think of a territory as "mine" or "belonging to me?"
Meanwhile, I got my first glimpse into a more reasonable explanation of why dogs mark -- one that has nothing to do with "territory" -- many years ago when I took my dog Freddie to a training session I had with a six-month Maltese male named Buckwheat who hadn't had much socialization with other dogs. Freddie's presence made Bucky a little nervous, but not to the point that he couldn't learn the games we were teaching him. However, at several key points during the lesson -- which was taking place in the dining room -- I put Freddie in a down /stay by a piano in the living room, to keep him out of the way. Later Bucky's owner told me that immediately after Fred and I left, Bucky had gone over to the piano and had urinated on the spot where Freddie was told to lie down.
Why did he do that? To mark the limits of his territory? He was already inside his territory; in fact, not even inside his territory but inside his "den." Did he do it to send a message to Freddie? The answer is simple: The rug held remnants of Freddie's scent. That made Bucky nervous so he put his own scent on top, to cover it up. Yes, in a sense, he marked the piano, but not to tell Freddie that it was his. If anything, he did it just to relieve his internal tension.
A few years later, while doing research for a subplot about kidney disease for my 4th novel, 'Twas the Bite Before Christmas, I learned that in mammals, the need to urinate is controlled, in large part, by the neuropeptide vasopressin. Higher levels of vasopressin increase water retention, reducing the need to urinate. Low levels are associated with excessive urination, bedwetting, etc. Vasopressin also has a converse relationship with the stress hormone, cortisol: when cortisol levels go up, vasopressin goes down, suggesting that there's a causal relation between stress and excessive urination.
So it seems far more likely that when one male detects the scent of another dog, (particularly an unknown male), it could cause a perhaps low-level stress reaction, which would then increase his need to urinate. As he does he would feel the pleasure of releasing some of the tension and pressure in his body. And thus, over time, his body would self-reinforce the behavior of peeing on top of another dog's scent. It would be a purely emotional and perhaps Pavlovian response, not based on intellect or other mental faculties.
Later, when this dog smells a urine mark he'd made earlier, he would probably re-experience, on some level, the original lessening of tension and the pleasure it produced. (Of the five senses the sense of smell is the one most likely to evoke memories.) He learns to mark in order to relieve emotional tension and to feel connected to his environment.
This explanation is simple, whole, and complete. It requires no complicated thinking on the dog's part. It obeys the rules of parsimony and logic. And it only requires that a dog have the ability to experience tension and pleasure, and to form simple physical and emotional associations.