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Dog Aggression

Dog aggression is any behaviour meant to intimidate or harm a person or another animal. Growling, baring teeth, snarling, snapping and biting are all aggressive behaviours.

Although aggressive behaviours are normal for dogs, they’re generally unacceptable to humans. From a dog’s perspective, there’s always a reason for aggressive behaviour. Because humans and dogs have different communication systems, misunderstandings can occur between the two species. A person may intend to be friendly, but a dog may perceive that person’s behaviour as threatening or intimidating. Dogs aren’t schizophrenic, psychotic, crazy, or necessarily “vicious,” when displaying aggressive behaviour.

Because aggression is so complex, and because the potential consequences are so serious, we recommend that you get professional in-home help from an animal behaviour specialist if your dog is displaying aggressive behaviour. Our Yelp Line can’t assist you with aggressive behaviour problems (see When to Seek Professional Help).

Types of aggression

Fear-motivated aggression

Fear-motivated aggression is a defensive reaction and occurs when a dog believes he is in danger of being harmed. It’s your dog’s perception of the situation and not your actual intent which determines your dog’s response. For example, you may raise your arm to throw a ball, but your dog, perceiving this to be a threat, could bite you because he believes he is protecting himself from being hit. A dog may also be fearfully aggressive when approached by other dogs.

Protective, territorial and possessive aggression

Protective, territorial and possessive aggression are all very similar, and involve the defense of valuable resources. Territorial aggression is usually associated with defense of property. However, your dog’s sense of territory may extend well past the boundaries of “his” yard. For example, if you walk your dog regularly around the neighborhood and allow him to urine-mark, to him his territory may be the entire block! Protective aggression usually refers to aggression directed toward people or animals that a dog perceives as threats to his family. Dogs become possessively aggressive when defending their food, toys or other valued objects such as tissues stolen from the trash.

Redirected aggression

This type of aggression is relatively common, but is a behaviour that pet owners may not always understand. If a dog is aroused into an aggressive response by a person or animal that he is prevented from attacking, he may turn this aggression onto someone or something else out of frustration. A common example occurs when two family dogs become excited, bark and growl in response to another dog passing through the front yard. The two dogs, confined behind a fence, may turn and attack each other because they can’t attack the intruder.


Predation is not really considered aggression, because it’s motivated by the intent to obtain food and not by the intent to harm or intimidate.

Dominance aggression

True dominance aggression is rare.

Dominance aggression is motivated by a challenge to a dog’s social status or to his control of a social interaction. Dogs are social animals and view their human families as their social group. Domestic dogs have loosely formed hierarchies which are fluid and can change with the situation.  A truly dominant dog, a real leader does not have to use aggression.

Canine rivalry

Canine rivalry refers to repeated conflicts between dogs living in the same household. Animals that live in social groups establish a loose social structure and the role of each dog can change with the situation.

In the past, rivalry between housemates was explained through the dominance theory, which states that there is a set pecking order between dogs and people in the household.  Research shows us that domestic dogs do not act like wolves and have a fluid social structure. They are not pack animals and do not establish a dominance hierarchy.

Dogs communicate with each other using subtle body language and this can reduce conflict and promote cooperation among group members. Conflicts arise between household dogs when there are miscommunications, personality differences, and competition for resources.

Initially, dogs may only snarl, growl or snap without injuring each other. Sometimes, however, the conflict may intensify into prolonged bouts of dangerous fighting which may result in one or both dogs being injured.

Individual variation

Dogs differ in their likelihood to show aggressive behaviour in any particular situation. Some dogs tend to respond aggressively with very little stimulation. Others may be subjected to all kinds of threatening stimuli and events, and never attempt to bite. The difference in this threshold at which a dog displays aggressive behaviour is influenced by both environmental and genetic factors. If this threshold is low, a dog will be more likely to bite. Raising the threshold makes a dog less likely to respond aggressively. This threshold can be raised using behaviour modification techniques. How easily the threshold can be changed is influenced by the dog’s gender, age, breed, general temperament, and by whether the appropriate behaviour modification techniques are chosen and correctly implemented. Working with aggressive dogs can be potentially dangerous, and should be done only by, or under the guidance of, an experienced animal behaviour professional who understands animal learning theory and behaviour.

What you can do

  • First check with your veterinarian to rule out medical causes for the aggressive behaviour.
  • Seek professional help. An aggression problem will not go away by itself. Working with aggression problems requires in-home help from an animal behaviour specialist.
  • Take precautions. Your first priority is to keep everyone safe. Supervise, confine and/or restrict your dog’s activities until you can obtain professional help. You’re liable for your dog’s behaviour. If you must take your dog out in public, consider a cage-type muzzle as a temporary precaution, and keep in mind that some dogs can get a muzzle off.
  • If your dog is possessive of food, treats or a certain place, don’t allow him access to those items. In an emergency, bribe him with something better than what he has. For example, if he steals your shoe, trade him the shoe for a piece of chicken.
  • Spay or neuter your dog. Intact dogs are more likely to display dominance, territorial and protective aggressive behaviour.

What not to do

Punishment won’t help and, in fact, will make the problem worse. If the aggression is motivated by fear, punishment will make your dog more fearful, and therefore more aggressive. Punishing territorial, possessive or protective aggression is likely to elicit additional defensive aggression.

Don’t encourage aggressive behaviour. When dogs are encouraged to “go get ’em” or to bark and dash about in response to outside noises or at the approach of a person, territorial and protective aggressive behaviour may be the result.