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Dog Behavior Varies With Height, Bodyweight and Skull Shape

How does a dog's physical traits relate to his behavior? By Claudia Bensimoun

According to new 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 that dog 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 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 for us to get up close to something and focus on it.) 

Pug photo courtesy of Kelly McFaul-Solem.
In past research, it was also demonstrated that dogs with long noses have more of a visual streak than those with short noses. Thus, the German Shepherd would have more sensitivity to movement for longer 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.
Canine size and head shape have been shown to influence behavior. Photos courtesy of Katie McKewen (left) and Carla Pavaravani (right).

The study demonstrated that 33 behavioral traits in dogs 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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