The average dog litter size is five to six puppies, though dogs can have anywhere from one to 12 depending on the size of the parents (the bigger the pooch, the bigger the litter). Dogs can have more, as the current Guinness World Record for the largest litter is 24 puppies born in 2004, but it's rare. Usually, most or all of the puppies from a litter are adopted out to different homes. Which may lead you to wonder, do dogs remember their siblings and littermates? And would they recognize them if reunited at some point?
Do Dogs Remember Their Littermates?
Although we don't know for sure, the answer is probably no. There is no concrete evidence that dogs remember their siblings, so it seems likely that they cannot distinguish between a dog that is their sibling and one that is not. That being said, there are many stories that provide anecdotal evidence to the contrary. So some do believe that dogs can recognize their littermates and have come up with a few theories as to why:
Imprinting In The Critical Socialization Phase
Dog behavior consultant, trainer and author of the Handbook of Applied Dog Behavior and Training, Steven R. Lindsay suggests dogs can remember their siblings - provided they stay together for longer than most. He theorizes that dogs can remember siblings, parents and even humans that they interacted with during the critical socialization phase from birth (or at least week three) through week 16. This is when the mom and her litter will bond through imprinting. During this biochemical process, the "love hormone" oxytocin plays a major role in the formation of a lasting connection where scent and appearance can later become triggers for remembering one another.
Research has shown that dogs can recognize and remember specific faces, such as their owner. In the study, dogs preferred their owner's face to that of a stranger and also paid less attention to the owner's face when it was covered. So if a dog can recognize another species, could they recognize and remember the face of a sibling? Maybe. This is merely speculation, though.
DNA And Evolutionary Instincts
Evolutionary theorists believe that all living animals are instinctually programmed to make sure their DNA survives for generations. Not only does this mean animals prioritize mating, it also means they may favor their family over others. For example, dogs descended from wolves, who live in packs of extended family members. It's engrained in their DNA to recognize their kin and distinguish between family, friend and foe (e.g. wolf mothers know which is their offspring and pups know who is their mom). This is part of their survival instinct for two reasons: inviting a stranger in to the pack could be harmful and assisting kin (by sharing food, shelter, etc.) can ensure viability. So this may imply that dogs could be one of the many animals that is able to recognize their family members.
Scent And Scent Memory
Dogs are extremely scent-oriented. Their noses are thousands of times more sensitive than ours. They can remember a previous smell, sometimes for long periods of time (and some smells stick with dogs for longer than others). So theoretically, a dog with longer scent memory may remember the smell of their sibling when reunited after a few months or years through their pheromones (hormones that animals can smell). Though they probably aren't labeling this dog as a sibling, they may feel comfortable more quickly given the scent is familiar.
Long Term Memory
Many studies - and real life events - have shown that dogs have long term memory. For example, think about all those heartwarming videos of dogs remembering their owners after lengthy military assignments. Dogs have also been observed acting differently when owners leave for long versus short periods of time, which suggests they remember something about how long ago their owner left. Furthermore, many rescue dogs who have been abused or neglected can carry those memories for a lifetime. So because we know that dogs have long-term memories, there's a chance they would remember siblings from their past. But how long a dog remembers something depends on the strength of the positive or negative impact when the memory was formed. This is often why abused dogs remember those events forever. So it seems dogs would have to have either an extremely good or bad experience with their littermates for this theory to come to fruition.
What Science Says
A study by The University of Belfast in Ireland decided to investigate whether or not dogs remember their family members. It's important to note that the research was performed in 1994, but the results were interesting nonetheless.
Researchers first tested whether weeks-old puppies could recognize their mom versus a dog of the same age and breed. They found that 84% of the puppies showed a preference for their mother. They then ran the same experiment with siblings versus other puppies of the same age and breed. 67% preferred their littermates.
The researchers also determined that these results were strongly related to scent. They did so by repeating the experiments but with cloths of their mother's and siblings' scents (created by having them sleep on the fabric for several days). The results were that 82% of puppies preferred their mother's scent and 70% preferred their littermates' scent.
Though this doesn't determine whether dogs remember their siblings, it does indicate they tend to prefer them over other puppies.
Next, the researchers looked into adult dogs. They used two year old dogs that had been separated from their mom and most or all of their siblings at eight weeks old, whose family members could be accessed. They first placed a cloth with the original puppy's scent alongside cloths from other puppies (who were now two) for the mother to smell. 78% of the time, the mother sniffed her offspring's cloth the longest. Then the researchers reversed it, placing a cloth with the mother's scent alongside other dogs of the same age and breed in front of the offspring. 76% of the time, the two year old dogs sniffed their mom's scent the longest.
Next the researchers tried the same experiment but with siblings. The results showed that dogs could only recognize their littermates' scent if they still currently lived with one. This demonstrated that dogs can use smell to remember their mother after being apart for years, but not their sibling if they are fully separated from them.
Signs Your Dog May Remember Their Sibling
Despite this study, there are many stories of owners who have reunited their dog with its littermates and believe they remember them. They say their dogs give them signs, such as:
- Reacting differently than with any other dog they meet for the first time, such as acting as if they know each other
- Sniffing more intently
- Appearing more calm and comfortable
- Wagging tail excessively
- Acting very attentive, alert and interested in their presence
- Staying close to the dog
- Acting overly excited
- Playing quickly and without conflict
On the other hand, lots of people report that their pups were no more excited to meet a littermate than other dogs. Some have even said their dogs were wary of their siblings when reunited, barking and eventually growling at them.
Perhaps, the dogs in all the stories did remember their siblings or maybe they just had a good feeling about them. There are many reasons why our pups like some dogs and not others. Also there are theories that dogs seek out their own breed, which can be a factor if your dog is purebred. All in all, we may never know for certain if dogs remember their siblings.