London - Plenty of dog owners are used to their pet’s frequent toilet stops at trees and lampposts during walkies.
But those with smaller dogs may not have noticed that they mark their territory more enthusiastically than bigger dogs.
Researchers have discovered that smaller breeds try to make up for their size by aiming higher than larger dogs.
The scientists say the smaller animals will lift their leg up to ten degrees wider so that their urine reaches a higher spot.
They say this gives a "dishonest" impression of their size when other dogs encounter the scent, and may be a way of warding off larger, more aggressive breeds.
Lead researcher Dr Betty McGuire, of Cornell University in Ithaca, New York, said: "Small males seem to make an extra effort to raise their leg high – some almost topple over. In our earlier study of scent marking and body size, we found that small dogs also urinate more frequently than large dogs and were more likely to direct their urine at targets in the environment, such as trees and poles.
"We informally refer to this suite of marking behaviours as 'the small dog complex'."
For the study, which is published in the Journal of Zoology, the researchers filmed 60 male dogs of varying size – mostly cross-breeds – as they left urine scent marks on their daily walks. They were able to show that the angle of their raised hind legs directly related to the height of the urine mark.
One dog called Patches, for example, raised his leg by 115 degrees and left a mark 15.3cm up the trunk of a tree. He later raised his leg by 120 degrees and urinated 17.8cm up the tree.
Dr McGuire found that smaller dogs raised their legs up to ten degrees higher on average than bigger dogs.
She said the small dog complex may help them avoid conflict with larger animals. She explained: "Direct social interactions with other dogs may be particularly risky for small dogs, given their lesser competitive abilities.
"Such risk might explain why small dogs seem to prefer communicating via scent marking, which allows an individual to leave a mark in the absence of another dog.
"It also might be uniquely beneficial for small dogs to exaggerate their body size and competitive abilities through relatively high scent marks if this enables them to avoid direct conflict. In contrast, large dogs, with greater competitive abilities, would have less incentive to avoid direct conflict."
She added: "We hope dog owners are intrigued and amused – and not at all concerned – should they see their small dog behaving in a manner consistent with the small dog complex."
However, Carys Williams of the Dogs Trust said smaller dogs may just be raising their legs higher to cover the mark that a bigger dog had left behind.