Training & Behavior

How Do Dogs Choose Their Friends? 

Here’s what we know our best friends’ best friends.

By The Farmer's Dog | February 3, 2025

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If you have a dog in your life, this story may sound familiar. My small terrier, Bonnie, is what behaviorists would deem “dog selective.” She has her posse of friends, most of whom she’s known since her first months on this earth. And she has, in my view, her sworn enemies—dogs in the neighborhood at whom she will growl and lunge until they give her space. After observing countless interactions that range from positive (play) to negative (unrepentant growling and lunging)—I’m no closer to understanding how she makes these choices or predicting which dogs she’ll like or dislike. 

In efforts to better (or, really, begin to) understand how dogs choose their friends, I enlisted some help from experts in relevant research fields and boots-on-the-ground behaviorists. I noticed our conversations would often stray from dog friendship to the nature of friendship itself. The question became: is there a universal definition of this kind of relationship for all humans? And if not, how can we begin to define one for dogs? What friendship is may change from person to person, and from time period to time period. It’s not unthinkable that this is true for dogs as well. 

It may seem that dogs have simpler relationships than ours, and that they communicate with each other in a clearer, more “honest” way. But we can’t know the inner workings of dogs’ social dynamics. In many ways, their personalities and relationships are likely just as complicated as ours, and teasing out the “why” of their bonds amounts to observing dogs’ behaviors and trying to recognize their choices when they make them.

What does the research say about dog friendship?

There are few studies on friendly social connections in dogs. “The big answer, somewhat disappointingly, is pretty much that we don’t know [how dogs choose their friends],” says Janis Bradley, Director of Communications at the National Canine Research Council. “Nobody has really tried to look at this. It would be quite difficult to set up a way where you had a large enough sample and controlled situations where you could actually draw any conclusions.”

A 2012 Time Magazine cover story questioned whether dogs could be “true friends”—to humans and to each other. Drawing conclusions from the available animal research, the story noted “the lack of evidence in dogs of the constancy, reciprocity and mutual defense observed in species such as chimpanzees and dolphins.” 

The author’s somewhat dour conclusion: “Dogs are neither our best friends nor one another’s—which is not to say they’re not warm and wonderful companions.”

So dogs failed the friendship test according to one set of criteria, but anyone who has watched two dogs play, live together, or even mourn each other’s absence would wonder whether dogs have their own set of criteria for successful friendships. Dr. Marc Bekoff, professor emeritus of Ecology and Evolutionary Biology at the University of Colorado, Boulder, and a Fellow of the Animal Behavior Society, holds dogs to a much simpler standard of friendship, and one that would seem to better align with who dogs are, not who chimpanzees or dolphins are.

“Of course they do [make friends],” Dr. Bekoff says. “I define friendship in a really generic way in the sense that dogs are friends when they seek one another out, when they like to hang out with one another, and they play. Do they look for the other individual when they’re not around? Do they rest and sleep together?”

It is, he notes, not so different from how he’d assess human friendships.

“Dogs form bonds the way that we do, or I can say we form bonds the way animals do,” Dr. Bekoff says. The sniffing and circling rituals are not so different from our exchange of pleasantries (though dogs may not share our insistence on making eye contact when meeting new acquaintances). 

“What [dogs are] looking for is some kind of reassurance that they’ll be accepted like we might be,” he adds.

When it comes to questions of interpersonal relationships among animals, observation goes a long way. But one 2014 study published in Proceedings of the National Academy of Sciences (PNAS) attempted to explain the mechanism by which strong bonds form between canines. The authors identified oxytocin as the neuropeptide that encourages dogs to form all types of relationships, including friendship.

The study defines bonds as “high rates of cooperative behaviors over time” and some of the behaviors indicating strong bonds included “trusting behavior, in-group cooperation, and generosity.” The authors found that giving extra oxytocin to dogs promotes a suite of behaviors directly related with social bonding. This “supports the idea that the same hormonal and neuroendocrine factors that promote parental behavior and pair-bonding in mammals also contribute to the formation of other types of social relationships,” according to the study’s authors. “These findings are in line with studies in humans reporting the effects of OT [oxtocin] on behaviors that facilitate interpersonal relations, from perception bias to social motivation to trusting behavior.” 

Said more plainly, the factors that go into parental bonds in dogs go into friendship bonds, and those factors are the same as what drives human relationships. 

Likewise, a recent study conducted by The Dog Aging Project, which is a 10-year study on dog health run by a cohort of scientists and research veterinarians, found that living with other household companions was a major factor in improving a dog’s health. 

“This suggests,” the authors of the study wrote, “that similar to humans, increased social enrichment in companion dogs is associated with health benefits, and also provides an example of an easily modifiable environmental intervention to improve dog welfare.”

What is more foundational to any definition of friendship for any creature than that it enriches the lives of those who participate in it? 

But how do I know who my dog will be friends with? 

Predicting whether or not two dogs will strike up a friendship is near impossible—or at least, it’s as difficult as figuring out whether two strangers will hit it off if thrown together all of a sudden. 

“If you think about the human analogy—and it’s often very, very useful to have that in the back of your mind when you think about dogs—well, what if I were talking about people?” Bradley says. “And it’s pretty hard to just look at two people who don’t know each other and about whom you don’t know anything and predict whether or not they’re going to get along.” 

Some dog owners swear their own pup has a vendetta against certain dog breeds, or can’t get enough of other breeds. While there’s no evidence that dogs differentiate between breeds whether through smell, sight, or other means, it’s not impossible that dogs could make assumptions based on other visual cues. For example, if a dog has good early experiences with, say, small, black dogs, they may be open to meeting small, black dogs in the future. As for scent as a marker of breed, there was a preliminary study on mice that’s now over a half century old that suggests a breed might carry with it a recognizable scent, but the theory has never actually been tested with dogs. 

Some breeds do tend toward specific play styles, and dogs may exhibit a preference for that style. Size can also be a factor as a means of determining play styles. Denise Herman, trainer and founder of Empire of the Dog, launched small-dog play groups in New York City many years ago with the intent of matching dogs safely and with similar styles of play. Even in the small-dog group, she separated dogs by breed and play style. “There are exceptions to every rule, but as a rule, Frenchies and Chihuahuas did not enjoy playing together,” she says. “Certain types of dogs seem to be more inclined to be air boxers or chasers whereas other dogs are wrestlers and biters.”

Or as Ren Vople, trainer and founder of GoDogPro, puts it, “Some dogs are tea-party dogs and some dogs are ravers.” 

Age can come into play as well because many puppies haven’t yet learned the dog decorum and communication skills that allow them to make friends with older dogs. 

“This is why we have puppy play groups,” Herman says. 

In the end, with everything from breed to play style to age, it’s good to remember that every dog is different, and will choose friends based on a criteria that’s as mysterious to us as a human’s criteria is for friendship. 

And how do I know when my dog is having a good time with friends?

The Dog Aging Project’s findings suggest that friendly relationships are essential in dogs’ lives, and that the more socializing with the same species, the better. But, again, not all dogs are the same. 

As Dr. Bekoff says, “First of all, I would say that everything else being equal, having friends and close social relationships is really important for dogs, but then again it depends on the personality of the dog. There are introverts and extroverts.” 

Putting dogs in situations in which they’re uncomfortable is a surefire way to stress them out, and may make forming friendships more difficult in the future. But because we can’t always predict which dogs will hit it off with which other dogs, we have to rely on in-the-moment action on the part of the dogs. Namely, do they choose to engage on their own? 

As Vople, puts it, “Playing never lies. Dogs, they’re not going to play when they’re stressed. They can’t fake it.” 

“The easiest [observable criteria] to look at in terms of relationships with any given dyad is proximity,” Bradley adds. “How do they vote with their feet? Do they vote to be relatively close to each other extremely close to each other? Do they vote to keep their distance? That’s something that could be studied and measured, and it’s fairly obvious.” 

This goes for those interactions where it may sound or look like the dogs are fighting, but it actually is all in good fun. Automatically assuming one dog’s growl or snarl at another means they don’t like each other can lead to you, the guardian, misreading or, worse, mishandling the situation. 

“Don’t pathologize dogs growling or even a little bit of snapping,” advises Herman. “Dogs don’t have lawyers. They solve conflict with that sort of stylized aggression.”

Barking aggressively doesn’t always mean, then, that our dogs are antisocial and rude. For young dogs and small dogs, that sort of behavior can build confidence. They discover a means of opting out of invitations to play or interact when they bark and the other dog backs off. This can often be good communication that helps build relationships over time. If the behavior seems to come from stress, seems like it’ll lead to injury, or it worries you as a dog owner, reach out to a certified trainer for help assessing. This is all to say that humans tend to be inadequate judges of dog’s social interactions, and we can’t assume much. 

To combat that inadequacy before you even head to the dog park or play date, Herman recommends familiarizing yourself with safe play techniques and body language, so you can know what you’re looking at when dogs play, and then follow their lead where possible. 

Setting dogs up for friendship success

There is an exception to the basic practice of following a dog’s lead when it comes to interactions and relationships. If there’s a secondary goal in mind, like, for example, if you have two dogs in your house or you’d like dogs within an extended family to get along (thus making things like vacations and holiday gatherings easier for all), then there are things you can do to encourage two dogs to get along. 

Introducing two dogs for the first time is best done at a neutral location. Starting in a neutral area far apart, so they can get used to the idea of one another is a good start. And if that goes well, take them on a parallel walk together, where they’re just walking alongside each other and not necessarily interacting. If that goes well, off leash play may be in order (read more about introducing dogs here). 

With some patience, it could be the start of… well, let’s just call it a beautiful friendship.

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