November 05, 2020 6 min read

Table of Contents

According tonew research from the University of Sydney and published in Plos One, the size of a dog and skull shape of a dog are important factors in a dog's behavior. Dr. Paul McGreevy from the University of Sydney's Faculty of Veterinary Science explains that certain types of canine physical characteristics can contribute to a dog's behavior.

More than 8300 dogs of over 80 different breeds were described in the dog owner reports used in this study. Dr. McGreevy and colleagues used the Canine Behavioral Assessment and Research Questionnaire (C-BARQ) and they also examined the sizes of over 960 dogs.

Dr. McGreevy explains how smaller dogs seemed to have more aggression issues, and thatdog behavior norms will depend on more than a dog's breeding. According to the research published in Plos One, certain physical characteristics in dogs such as height, body weight, and skull proportions (length and width of the skull) are linked to certain types of behavior.

Skull and Eye Size

A dog's skull length can vary from 2 ¾" to 11". With a wolf's skull measuring 11 ¾", a dog's skull can be similar in size.

Despite this variation, there's not much variation in dogs' eye size across different breeds. (Although Chihuahuas have a large eye size compared to skull size. Usually, dogs with larger skulls will have larger eyes.) Earlier studies have shown that a dog's eyes usually measure with a radius of 43".

Cells in the retina of an animal's eyes are all arranged differently so as to give different and most appropriate types of vision for the animal. Eye cells are concentrated horizontally across the retina. This is known as a "visual streak," and it gives animals more sensitivity to movement in their visual field. (Humans, on the other hand, have eye cells concentrated in the area called area centralis, and this allows us to get up close to something and focus on it.)

In past research, it was also demonstrated that dogs with long noses have more of a visual streak than those with short noses. Thus, theGerman Shepherd would have more sensitivity to the movement for long distances around him than a Pug would (Pugs have almost no visual streak). Scientists say that the variety of the distribution of eye cells in a single species like a dog is unique.

As a result of selective breeding, many dogs (like Boxers and Labradors) have retained puppyhood features. This new study demonstrates that a dog's eye and brain structure relates to his skull size. The smaller the dog, the more behavioral quirks a dog owner may face like humping, urinating indoors, or excessive barking.

The study demonstrated that 33 behavioral traits indogs correlated with height alone. Some of these are:

  • mounting persons or objects
  • touch sensitivity
  • urination when left alone
  • dog-directed fear
  • separation-related problems
  • non-social fear
  • defecation when left alone
  • owner-directed

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Testing Methods

  • 12 show dogs tested (6 females, 6 males), and the study was approved by the New South Wales Animal Ethics Committee. None of the dogs were distressed.
  • Dogs were 2 years and older, of show quality, or from show pedigree lines. All pups from the show dogs that have already been measured were not taken into consideration so that the data was not used twice.
  • Dog breeds had to be ANKC (Australian National Kennel Club) recognized.
  • Dogs had to be owned by registered breeders only.
  • Dogs have had to have had over 30 puppies registered yearly with the ANKC in 2009. These dogs were then photographed and measured. The camera was held horizontally. This allowed for a true measurement that included the skull’s length and width
  • Heights and weights were also used from the ANKC breed standards. When males and females of the same breeds had different heights, the scientists used the mean height.

There were 6 breeds that had no ANKC preferred height standard, so the scientists went to and drew information from there. Weight information was drawn from theC-BARQ database.

What is C-BARQ?

C-BARQ is a survey completed by dog owners that are designed to provide quantitative assessments of many common behavioral traits in dogs.

The questionnaire has 100 questions using a 5-point rating scale (0 meaning the behavior is non-existent, and 4 indicating that the behavior is the most intense.)

Questions related to a dog’s usual response to many everyday situations like fear, excitability, and aggression.

There are 14 behavioral factors tested with an additional 22 traits tested. The higher the scale rating result, the less favorable except for the trainability of the dog, in which case the higher scale score the better.

Scientists were wary of the biases associated with dog owners and questionnaires such as behaviors they didn’t like in their dogs. Other behaviors may be overlooked, like defecating in the home, as opposed to excessive barking when left alone. They also took into consideration that, in some cases, attention-seeking behaviors have been triggered by the dog owners themselves.


There seems to be an interesting correlation between behavior and morphology in the canine species.

  • “Undesirable” behaviors increase as the size and height of a dog decreases.
  • Short-skulled dogs had an increase in grooming and compulsive staring.
  • Long skulled dogs had an increase in stranger-directed fear, persistent barking, and food stealing.
  • More stranger-directed aggression was seen from smaller breeds similar to the terrier breeds. Researchers questioned whether there was a simultaneous selection for aggressiveness in smaller breeds related to their past history. Terriers were used for chasing and hunting prey underground. Smaller breeds that have short legs may have inherited aggression.
  • This study also questioned the behavioral responses of smaller breeds with owner-directed aggression and linked that to the attachment and attention-seeking behaviors in dogs linked to jealousy and pushiness when a dog’s owner’s attention is given to someone else. Scientists refer to this as resource guarding.
  • Larger breeds descended from smaller breeds that were originally meant to be companion dogs (like breeds that come in multiple sizes) may display behaviors that do not match up with their body size.
  • Dogs with a higher C1 had greater central visual field acuity. These dogs would be more able to see and focus on objects in front of them, instead of on objects in their peripheral vision. These dogs would not then be able to scan objects in the distance, thus resulting in a reduced chasing response.
  • Fly-snapping, a compulsive disorder, according to an earlier study done by Dr. McGreevy (2009, A Modern’s Dog’s Life, UNSW Press, Sydney), may indicate stress factors. The researchers found that fly-snapping was not related to the height of the dog, but more so to the weight. That said, shorter and stockier dogs, like the Bulldog, were more at risk for displaying coping behaviors. It is unclear why they do so.
  • Obsessive tail-chasing behavior was not linked to size or breed. Tail-chasing, according to a study done by Dr. Osmo Hakosalo and colleagues and published in Plos One (2012, Environmental Effects on Compulsive Tail Chasing in Dogs) is associated with other factors.
  • Trainability was the only behavioral trait associated with increasing height in dogs.

Researchers also took into consideration that smaller dog breeds are known to be genetically associated with neurological changes in how they react to environmental stimuli or changes in their environments. Smaller dog breeds react more frequently to stimuli in their environment compared to larger dog breeds that are more laid back.

The research also showed that breeds that were not as heavy were more prone to being excited, hyperactive, and energetic compared to heavier breeds like the Bull Mastiff. The study also questioned whether the likelihood of smaller dogs being kept indoors more often and being exercised less frequently due to their size were contributing factors to behaviors that were similar to those in puppies.

According to this study, it’s nearly impossible to find out about the role of a dog’s early environment in the emergence of undesirable canine behaviors. Yet many of a breed’s behavioral dispositions are very much related to skull shape, so, in fact, the size of a dog has less influence on a dog’s behavioral dispositions than the shape of a dog’s skull.

According to the study, there are strong correlations between a dog’s body size, skull shape, and behavior among all breed types. Researchers don’t know if this is because of functional adaptations that dogs have had to make or whether these are accidental changes.

Researchers also have not been able to determine from the data the extent that the correlations between body size, skull shape, and behavior were caused by genetic or environmental factors. Nonetheless, the results demonstrate that domestic dogs are a great model for studying the biological processes that are responsible for behavioral and body type diversification.

First Published in the United States Dog Agility Association (USDAA) &The World CynoSport Rally.

Meet The Author

Claudia Bensimoun

Claudia Bensimoun author of Dog Behavior Varies With Height, Bodyweight, and Skull Shape

Claudia Bensimoun is a freelance journalist and author, and specializes in veterinary content, and eBooks. She's a long-time feature writer for Animal Wellness magazine, Fido Friendly magazine, and the United States Dog Agility Association. In addition, Bensimoun has written for numerous pet websites, magazines, newspapers and online publications. Her interests include wildlife conservation, animal welfare, disaster/ humanitarian relief, veterinary research, and veganism.