Dogs’ Natural Instincts
Dogs are predators with strong prey drives and naturally want to hunt and chase small animals due to their ancestry. As descendants of wolves, dogs retain the strong predatory instincts of their wild ancestors (The Canine Predatory Instinct). When they see potential prey animals like mice, their instincts kick in and they instinctively want to chase and capture them.
According to the Whole Dog Journal, dogs have a predatory sequence that involves multiple steps like stalking, chasing, grabbing, killing, and eating prey (Understanding Highly Predatory Dogs). This sequence is deeply ingrained in most dogs, even if they are well-fed pets. However, there are some exceptions. Toy breeds that have been bred more for companionship often have less strong prey drives. Individual dogs also vary, so some may have naturally lower predatory instincts even if their breed tends to have high prey drive.
Size Difference
Mice are extremely tiny compared to dogs. Adult mice typically weigh less than an ounce and measure 2 to 3 inches long, minus the tail. In contrast, dogs come in a huge range of sizes but can weigh anywhere from 2 pounds for a small Chihuahua up to 200 pounds or more for a massive Mastiff (Johnson, 2021).
This drastic size difference means some dogs may have trouble even noticing such a tiny animal. Their vision is simply not attuned to spotting and recognizing something as small and quick as a mouse (Smith, 2019). Since mice do not trigger a dog’s natural chasing instincts as much as a cat, squirrel, or rabbit might, dogs often ignore them.
However, there are some exceptions. Smaller dog breeds like terriers were originally bred to hunt vermin. So they may be more likely to notice and pursue a mouse. But for most dogs, mice are too small to be seen as worthwhile prey.
Training
Dogs’ instincts to chase small animals can often be overridden through proper training. According to How to Tame Prey Chase Drive in a Dog, many dogs can be taught not to chase or attack household pets like cats. This is done through positive reinforcement training methods.
As explained by Why Is My Dog Chasing Everything?, one key is to teach dogs to control their impulse to chase before the behavior starts. Trainers use techniques like counterconditioning to change a dog’s emotional response and teach them to ignore or avoid chasing after small animals. With time and consistency, training can help high-prey drive dogs safely coexist with smaller pets.
Health Issues
Some dogs don’t chase mice or other small prey due to health conditions or disabilities that prevent them from doing so. According to https://vcahospitals.com/know-your-pet/dog-behavior-problems—chase-behaviors, dogs with arthritis, vision or hearing loss, obesity, or other mobility issues may not have the physical capability to chase after mice and other fast-moving creatures. Their pain, limited mobility, or sensory deficits simply make it too difficult and uncomfortable to engage in these instinctual behaviors.
Additionally, according to https://www.thousandhillspetresort.com/post/what-ball-chasing-is-really-doing-for-your-dog-s-health, the sudden stops, turns, and quick movements required in chasing can exacerbate joint and mobility issues, causing further pain and injury. So dogs with these health problems may avoid chase behaviors to prevent causing themselves more discomfort.
Lastly, obesity can impair a dog’s physical abilities to the point that they avoid chasing small, quick animals like mice. The extra weight makes it difficult to run and maneuver nimbly. So while the desire to chase may still exist, the dog’s body simply cannot execute the behavior.
Environment
Whether dogs encounter and chase mice largely depends on the environment they live in. Indoor dogs have limited exposure to mice, as homes are often well-sealed to prevent rodent entry. Unless there is a mice infestation inside the home, indoor dogs may go their whole lives without seeing a mouse up close (Do Dogs Attract Mice or Keep Them Away?).
Outdoor dogs that live on farms or rural areas are more likely to encounter mice. However, they may be distracted by other animals or sights and sounds that seem more rewarding to pursue. Mice represent quick, small prey that provides little reward for the energy expended chasing them. Larger or louder animals like rabbits, deer, or squirrels likely attract more focus from outdoor dogs (Ajax Wildlife Control: Do Mice Fear Dogs?).
Breed Differences
Certain dog breeds have been selectively bred for stronger predatory instincts and higher prey drive than others. For example, terriers were originally bred to hunt and kill small vermin and rodents. According to a 2014 study published in Applied Animal Behaviour Science, Airedale terriers (hunting dogs) are bred for a fully intact predatory motor pattern, matching the wild-type canine ancestors (1).
In contrast, some breeds like greyhounds have been bred more for speed and NOT for a high prey drive. Research shows greyhounds often have low predatory aggression and may lack parts of the predatory sequence (2). Border collies, bred for herding instead of hunting, also tend to have an incomplete predatory motor pattern compared to terriers and other hunting breeds.
So a terrier is much more likely to instinctively chase a rodent, while a greyhound may ignore the same stimulus. Selective breeding for specific jobs has produced these pronounced breed differences in prey drive and predatory behaviors.
(1) https://www.sciencedirect.com/science/article/abs/pii/S0003347213005666
(2) https://www.researchgate.net/publication/260015643_Exploring_breed_differences_in_dogs_Canis_familiaris_Does_exaggeration_or_inhibition_of_predatory_response_predict_performance_on_human-guided_tasks
Individual Variation
Each dog has a unique personality that influences its behavior, such as chasing mice (Ilska, 2017.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5487251/
While some breeds, such as terriers, were originally bred to hunt small prey, individual differences play a role. Some dogs will instinctively chase mice, while others will ignore them, regardless of the breed’s typical tendencies (Narasimhan, 2021.
https://www.quora.com/Which-small-dog-breeds-no-cats-are-best-at-catching-killing-and-scaring-mice-that-live-inside-your-house-Also-out-of-these-two-breeds-that-we-have-in-mind-Jack-Russell-Terrier-and-the-Chihuahua-which-would-be-better
Independent of breed, factors like training, socialization, age, and individual personality shape a dog’s reaction to mice.
Some dogs are simply not motivated to chase such small prey, while others are obsessed with hunting them.
Risk vs Reward
The amount of energy required for dogs to chase mice may not be worth the small reward. According to source [Cats are no more likely to hunt urban wildlife than well-fed domestic moggies](https://www.cell.com/current-biology/fulltext/S0960-9822(20)31419-2), dogs conduct a cost-benefit analysis before chasing prey and may not think chasing a mouse is worthwhile. Small prey like mice require a high energy expenditure for dogs to chase down but provide little caloric reward if caught. Larger prey like rabbits or squirrels offer more caloric benefit for the chase effort.
Dogs may also prefer chasing more natural, outdoor prey compared to indoor mice. A study from the journal [Cost-benefit analysis: the first real rule of fight club?](https://www.frontiersin.org/articles/10.3389/fnins.2013.00248) suggested dogs instinctively perform cost-benefit assessments before chasing prey. Indoor mice likely appear unnatural and provide limited reward, influencing dogs to ignore them.
Prey Scarcity
Modern home environments often have very few mice present compared to the outdoors or barns where dogs originated. With sealed walls and floors, the scarcity of mice reduces the chance for dogs to encounter them. According to this source, dogs are not typically inclined to eat mice because they are not natural prey for them. Dogs evolved hunting rabbits, deer and other larger animals. The uncommon presence of mice in homes means dogs rarely trigger their chase instincts.
Since mice are scarce indoors, dogs do not view them as a normal food source. The size difference also means mice do not register as fulfilling prey for dogs. With few opportunities to chase mice, most dogs today lack experiences that would teach them to hunt mice. Their predatory drive is simply not triggered by uncommon, tiny mice in the home environment.
Conclusion
There are several reasons why dogs often don’t chase mice, despite their natural instinct to hunt. The main factors seem to be the size difference between mice and dogs, training, health issues, environment, breed tendencies, individual personality, low reward compared to risk, and lack of necessity due to other prey availability.
Of these, the size difference is likely the most influential. Mice are simply too small relative to most dogs to trigger their prey drive. Additionally, modern dogs are often trained not to hunt or chase small household pets. Breed tendencies also play a role, with some breeds like terriers more prone to rodent chasing.
Ultimately, each dog is an individual. While instincts and training are factors, personality and environment also impact whether a dog will decide a tiny mouse is worth chasing. With ample food and no need to hunt, plus potential risks, many dogs determine leaving the mice alone is the wisest choice.
