For dogs, urine is a sort of Facebook profile of their personal life.
Both male and female dogs compete for status with their urine.
High-status male dogs are the most inclined to overmark, meaning they urinate over the mark left behind by another dog.
Dogs may compete with urine before they even meet, with scent marks providing information about an individual's health and more.
It's a dog-urinate-on-dog-urine world, concludes an extensive new study on canine scent marking. Both female and male dogs compete for status using the height, leg-lift angle, location and quality of their pee.
Published in the latest issue of the journal Animal Behaviour, the study is the first to find that countermarking (when a dog whizzes on or near where another dog previously went) is done more by high-status dogs.
"Previous studies on dogs really only found support for overmarking (peeing over pee) being something that males did, and that they mostly did it in response to female urine. So the previous interpretation was that male dogs overmarked to hide female urine," co-author Anneke Lisberg told Discovery News.
"Our patterns really broaden this understanding. Both sexes do it; both sexes countermark in response to same and opposite sex urine, and status is an important factor," added Lisberg, a researcher in the Department of Biological Sciences at the University of Wisconsin-Whitewater.
She and colleague Charles Snowdon conducted two experiments. The first involved presenting urine from unfamiliar "donor" dogs of various breeds to 48 privately owned Labrador retrievers. Each retriever was guided on a leash through a "urine course" where the dog could sniff, whiz or otherwise react to pee-marked wooden stakes.
For the second experiment, the researchers observed canine urine interactions at the off-leash dog park Muttland Meadows in Grafton, Wis. The scientists documented 153 urinations and 199 urine investigations from 87 male and female dogs of different breeds.
The dogs included individuals that were either fixed (spayed or neutered) or not.
For both experiments, the researchers also measured each dog's tail base position, which prior studies found signals status. It's believed that the higher a dog's tail is raised, the more status the canine generally enjoys.
Lisberg and Snowdon determined that males and females were equally likely to whiz next to an unknown dog's previous urine mark. High-tailed/high-status dogs, however, were far more active than other dogs at countermarking and investigating urine.
"Although both sexes countermark, they do it a little differently: Males are more likely to overmark than females, and high-status males exposed to a place like a dog park are the energizer bunnies of marking," Lisberg said. "Males and females investigate urine, and the higher tailed dogs of both sexes urinate and countermark. But the males don't stop after the first mark or second or third."
Some more submissive, low-status dogs will not countermark at all when visiting dog parks. Studies on other animals that also mark with urine suggest that it's risky for a submissive individual to even fake an overmark by standing on tiptoe while peeing or just lifting a leg with nothing coming out. Lisberg suggests that if a dog chooses to "throw its chemical hat into the ring," the canine better be able to deliver on the status it conveys via its pee and leg lifting power move.
"Because these are signals that can be investigated from a safe distance, it may be that dogs are able to sort out a lot of their relationships through marks before they ever meet face to face," she explained. "If they can sort out things chemically, it could help them make smarter decisions about whom to approach and how to approach them.
Michael Ferkin, a professor of biology at the University of Memphis, told Discovery News that the new study is "timely and interesting."
"The data the authors collected support and augment similar findings that were used as the basis for hypotheses to explain the functional significance of countermarking in other animals, such as mice and voles," he said.
Lisberg and her team are now studying other aspects of dog urine, such as how spaying and neutering may affect countermarking as a form of communication. Such communication is important, because she thinks it's possible dogs "might be able to assess many personal aspects of health, stress, virility, diet" and more just by sniffing another dog's urine.
She concludes that countermarking is "a sort of Facebook of their personal life, easily accessible from a safe distance."