Dogs being walked by men are four times more likely to threaten and bite other dogs and dogs on a leash are more likely to act aggressively than dogs off the leash.

These are just a couple of revelations about dog walking behavior from an extensive new study that examined how a dog’s age, sex and size, as well as the owner’s sex and use of a leash affect how canines act on their walks.

The study, accepted for publication in the journal Applied Animal Behavior Science, surprisingly found that the sex of the owner had the biggest effect on whether or not the dog would threaten or bite another dog.

“We propose that the occurrence of threat and biting in dogs on a walk may have some connection with aggressive tendencies and/or impulsivity in people,” Petr Rezac and his team wrote, adding that “dogs are able to perceive subtle messages of threat emitted by another dog. Simultaneously, dogs are unusually skilled at reading human social and communicative behavior.”

Rezac is an associate professor in the Department of Animal Morphology, Physiology and Genetics at Mendel University. He and his colleagues studied close to 2,000 dog-dog interactions on owner-led walks held in the city of Brno, Czech Republic. Observations were made in the mornings and afternoons at 30 different areas of the city where owners frequently walk with their dogs.

By far the most frequent interaction of dogs of all ages in public places was body sniffing, which should not come as a surprise to most dog aficionados. Other expected conclusions: males sniff females more often, males and females prefer play with each other than with members of their own sex, adult males mark the most, puppies play together more than twice as often as adults and 11 times as often as seniors, and dogs prefer to play with similarly sized individuals.

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The presence, or not, of a leash can make a big difference.

Dogs off a leash sniffed one another more often than dogs on a leash. They also threatened each other twice as often when on a leash.

“This is most likely a reflection of the frustration dogs feel when the leash prohibits them from expressing normal greeting behaviors,” Inga Fricke, director of Sheltering and Pet Care Issues at the Humane Society of the United States, told Discovery News. The problem, she said, even has a name: “leash frustration” or “leash aggression.”

Lisa Peterson, spokesperson for the American Kennel Club, said dogs prefer to run around each other when they first meet.

“They can’t do this run-around behavior when on a leash and they likely feel more threatened,” Peterson said. “They are also more inclined to resource guard, with the owner being the resource. It’s as though they are communicating, ‘He is my owner. I don’t want you to have him because he feeds and cares for me.'”

Another finding from the study is that female dogs enjoy playtime with males as well as other females, but males are a bit less inclined to play with other male dogs.

“That makes sense,” Peterson said, “because females rear litters of puppies and must play with them. It’s a nurturing thing so they are probably genetically predisposed to play more.”

As for the connection between male owners and dog bites/threats, Peterson said it could be a cultural phenomenon perhaps tied to how men train their dogs in the study’s region.

Fricke added, “The increased incidence of bites when dogs are being handled by males, rather than females, may simply be a reflection of dogs mirroring the emotions of their handlers; if their handlers are acting either defensively or assertively upon meeting, their dogs are likely to sense and reflect that.”