Aggression is a difficult topic to explain and treat. First, we want all dogs to get along, and it is hard to understand why dogs that were friends are now in conflict. Second, it is hard to find research studies on dog fights because of the obvious difficulty and danger of working with aggressively stimulated dogs. Third, there are long standing biases and rivalries in different fields of behavioral theory, with one side focusing on “nature” (genetics and inheritance) and the other focusing on “nurture” (learning and life experiences). Lastly, we see the simple truth: if aggression was understood and controllable, we’d have no need for laws, police, or prisons. The truth is that aggression is both reflexive (nature) and instrumental (learned).
Nature
Social competition is normal and to be expected in all mammal species, and in most species the males do most of the fighting. Male dogs will seek out a challenge to other males in their group. In other words, they want to compete. The competition builds into an aggressive emotional state as a male dog tries to restrict the freedom of behavior of another male dog. Rank can be won if a dog can become successful at controlling food; physically able to push the other dog around; can earn the reception of a large percentage of appeasement behaviors from the other dog; and create social (rank) and physical (territorial) distancing.
Sometimes it is easier to understand something when you look at it from another angle. In tournament species such as lions, elephant seals, elk engage in fierce same-sex fighting. Fighting is triggered by the presence and fight seeking competitive behavior of the rivals. The competition between male competition is to cause avoidance, death, dispersal, submission, or weakening (physical Injury) of a rival to obtain the resources acquired by rank. The males are highly aggressive and compete for dominance. Parenting is typically handled by females. Males tend to be bigger than females. We somehow “get” that these males in these species are “looking for a fight.” It begins with hormonal changes and sparring. Displays increase as mating time approaches. Smaller males tend to avoid the bigger and stronger males. Once a fight is picked, the participants are at risk of being injured or killed. Intraspecific aggression is for social organization, population dispersal and sexual selection. It has distance increasing functions. Ritualized aggression (such as gestures and postures) is a buffer between a test and a real fight. Rituals like this increase distancing without breaking down affiliative contact. And aggression is usually going to start out being more intense against an outsider coming in to take over than with an insider attempting to gain rank.
A version of this pattern also goes on with dogs. The difference is that male dogs don’t need female dogs in heat to enter the fray. Male dogs don’t need to be intact to get into fights, since their brains were wired to be male in the womb. Puberty stimulates males to engage in more risk taking and have more physically aggressive taunts. Males, especially adolescents, are motivationally driven to enter competition with other males as part of sorting out what will be their adult rank within a group.
Social competition has three phases. First is the testing phase, which includes mostly postures and gestures. Next, is the sparring. Lastly, if it gets that far, a real fight. If the fight isn’t settled quickly, then it becomes angry. The angry fight risks that the relationship is broken, and the dogs might not be able to safely live in the same home again. In human terms, they now hate one another.
Adult male dogs tend to be intolerant of adolescent male dogs. Adolescents are more provocative to adult males and tend to initiate the fights. These youngsters will provoke the older males with challenging gestures and postures (staring and threatening eye contact, snarl, showing teeth, puffing up in size), and engage in rude contact (dominance testing). Young males will intrude upon situations occupied by the higher-ranking dog, such as taking or interfering with possessions, places, and persons. It isn’t unusual to see a confrontation over a bed, furniture, sleeping area, crates, doorways, rooms. Or standing over or between objects and resources such as food, prized objects, or favorite person or pet. Or to engage in auditory stimulation such as growling or barking in a threatening tone. It is the role of the dominant dog to punish the challenger. Dominant dogs will stand over, assume a T-orientation; rest their head on the other’s shoulders; ride the other’s back; grab the scruff, grab the muzzle; or engage in body bumping and hip slamming. It isn’t unusual for a fight to take off when both dogs bang into each other as they go through a tight passage at the same time.
It can be dangerous to get in between two rivals. More violent attacks happen when dogs sorting out rank order are being physically disciplined by humans.
Male assertiveness, because of the selection preferences of females, tends to result in rivalry entailing more frequent and aggressive incidents of violence. Males tend to not be caretakers of the young and can recognize their own offspring and tend to not harm them. Males are more likely to harm puppies that are not related to them when entering a new territory or if those puppies enter their territories.
Learning
Aggression can be modified through learning. Animals can be trained to more frequently respond with aggression. Certain stimulus cues can be established to then trigger predictable emotional responses leading up to a fight. Aggression can increase the rank of the successful aggressor because it increases the potential effectiveness to compete for vital environmental resources. Aggression tends to be targeted at perceived lower ranked conspecifics. If the dogs can sort out their rank without injury or death, the fighting stops, and in that case, learning is beneficial for their relationship.
Animals’ brains are wired to expect rewards for what they do. The goal of social competition is control over a vital resource, situation, or behavior. Aggression has the function of increasing the probability control when peaceful means aren’t coming across as working. Aggression results in a set of violent motor patterns which are the product of sufficiently frustrated combinations of stimulated emotional states. The greater the frustration, the greater the aggressive response. Thus, if a goal fails to be met, aggression can result. Anger circuits can then be activated and received through various pathways throughout the brain as a way of increasing the potential for achieving that goal through the injury or elimination of another living target. Learning takes place. Ferocious responses in some circumstances lead to success.
Successful combat enhances survival, improves confidence, and lowers the threshold for engaging in future combat. This is why I’m not a fan of most dogs using an off-leash park. Once a dog has been in a fight, they are more likely to get in another fight. The winner is emboldened, and the loser has been deeply upset and will be more likely to be afraid and react in the next social encounter with a strange dog. Anticipation of an aversive event can trigger aggression. Such learning is extremely resistant to extinction. A natural trigger can come under the control of a conditioned stimuli (trigger). Environmental associations can also prime a dog to be aggressive, such as location or certain people or social situations.
After a fight, any negative feelings can be externalized towards some other animal or human, causing the dog to “blame” them for the evoked feelings. One of my students broke up a fight between her two female Cane Corsos. One of them changed towards her after that, and it wasn’t safe for her to be alone around that dog. She became part of the fight and those feelings transferred over to her and damaged their relationship.
How the confrontation turns out, either in success or failure, will result in learning. While humans can choose whether to be angry or not, animals can’t do that. Previous aggressive responses are easily remembered. Successful outcomes result in positive emotions which are highly rewarding.
Socialization
The role of socialization is to let young puppies develop the social skills to be able to engage in competent ritualized aggression and to hold back on escalating into a full fight. We make a huge mistake not heavily socializing puppies with other puppies, stable adult dogs, and humans during the first 4 months of life. Insecure, clumsy, socially incompetent dogs can’t respond appropriately to social pressures. They often don’t have a learned solution to reach some kind of compliance. Aggression can be reduced by behavioral rituals enhanced through socialization that potentially signal and prevent conflict, such as: submissive behaviors (such as appeasement behaviors like fawning, licking, tail tuck, ears back, postural diminution, grin, clack of teeth, pawing, play bows, crouch with a twist showing the belly, attention seeking; leaning; trying to get in your lap; mouthing; jumping up); and dominance behavior (such as rituals of combat, territorial behavior, and threatening). Avoidance offers social and physical safety, escape from threatening rivals. Avoidance can be displayed by running away, averting eye contact, hiding, stopping what they are doing, submission, and other displays of inferiority.
Bonds and familiarity tend to reduce aggression. Socialization helps foster good relationships and bonds. Broken bonds, unfamiliarity, and anti-social behavior (which includes “unfair” play), triggers aggression which is less inhibited and more violent.
Triggering Emotional States
Three basic emotional states tend to be the precursors to aggressive attacks: Seeking, Fear, and Panic. Seeking: Seeking is self-stimulating and is about fulfilling desires. Fear is reactive and about escape and avoidance from pain, injury, or death. Fear triggers aggression when escape or appeasement is thwarted. Initial signs are barking, licking, agitation. The more often fear triggers successful aggression, the fear threshold lowers, and the dog shows more confidence in attack as a means of defense. And Panic is the need to be part of a social group and distress from separation. Frustration of any of these systems can produce an aggressive emotional state. There are other such systems which can trigger aggression, but they are less well researched.
Thus, competition for, or frustration, of seeking can trigger possessiveness of a resource, typically a toy or food item and result in a fight if pushed too far. Backing a dog by into a corner and threatening them can result in a defensive aggressive response. And two dogs competing over a female can escalate into a full-blown fight.
Social Facilitation
The presence of more dogs increases the potential for aggression. It can increase territorial aggression. It can result in mobbing attacks. The more dogs present in each area, home, or situation, the more likely there will be a fight. It isn’t always wise to adopt that next dog.
Age of Dog
Age is a predictor of aggression potential. All puppies engage in considerable bouts of aggressive play. The belief is that aggression teaches bite inhibition and allows social learning of rank. The average age of dogs involved in serious attacks is 3 years old, and manifestations of aggression that warrant concern begin at about 1 year of age. Sufficient early socialization can blunt the potential for serious aggression as adults.
Territorial Threat
New dogs introduced into the home increase the potential for violence. The closer the home dog is to the familiar home range, the lower the threshold for engaging in self- and group defense. Increased population density in the home increases the propensity for territorial aggression. In the home, the home dog will defend his personal space, toys, food, places and passageways, and access to favorite people and pets. You’ll see the more dominant dogs tend to urine mark more frequently when the new dog is brought in, and he will urinate over the top of other dogs’ urine deposits. Frequent territorial intrusions increase territorial aggression, and it is hard for a home dog to have multiple new dogs coming and going through the home, as many foster rescue volunteers have experienced.
Training
Most aggression must be supervised and managed in an ongoing manner. It can’t be completely removed with a quick 2-week training course, since mammals can’t be transformed into something else just through training. Good training creates predictable streams of information and experiences for all the dogs in your home through proper supervision and management.
The role of dog training is to attempt to prevent the frustration of various emotional states which could result in aggressive responses. The better you can manage your dogs, the quicker you can stop the escalation of posturing into a fight. Fully training your dogs, gaining good dog handling skills, knowing the triggers, teaching manners, proper nutrition, and exercise, permitting and encouraging fair play, setting boundaries, and stress reduction are the typical approaches that reduce the risks.