To understand why dogs fight, you must first understand how their pack structures work. Now, there is much debate on pack structures now-a-days, so don’t be surprised if you hear something different from someone else. I’m pretty sure I’ve covered pack structures in a different blog entry, but I’ll go ahead and discuss it a bit here.
First you need to know that if you have a dog as a part of your family, you are in a pack structure whether you know it or not. If you are one of those people or families that has a couple of dogs in the back yard all the time that you just feed and water, then you most likely have two packs in your household; the dogs, and the humans (and don’t think dogs don’t know the difference). But I want to focus on those of you that actually interact with your pooches on a daily basis. These are people that walk their dogs, play with their dogs, train their dogs, feed their dogs, and keep their dogs indoors with them for the most part. You folks are in a pack with your dog(s). However, even though you are in a pack with your dog, that does not automatically make you the leader, or "alpha." Pay attention, because what I’m about to tell you is verrrrrry important. How do you know who the leader or "alpha" is? The leader always eats first, goes in and out of doors first, lays in the most comfortable places, and lays claim to everything that he/she is interested in. If your dog(s) truly respects you he/she/they will not eat until you have finished eating, even if they have food in their bowls! This is a natural, innate, behavior. The reason for it is too show respect for the leader, and to see if the leader will drop food that is deemed more valuable for consumption. This brings us to the first reason dogs fight…. food. Dogs have a loose ranking system that is very primative, but it helps them set priorities as to what is more important. Food is high on the value list. In the dog world, you either fight, flee, avoid, or submit. Food, unless taught otherwise, is worth fighting for. There are a surprising number of dogs with "food aggression" issues because they’ve learned that the only way they will get to eat their food is to fight for it. Some dogs fight for it because another dog or person is stealing it, or I’ve even had a case where the dog displayed "food aggression" simply because the owner was not feeding the dog enough food. The dog was a growing yellow labrador puppy that was only getting half a cup of food twice a day. When I recommended that the owner increase the amount of food at feeding time and gave them a week to do so, the "food aggression" went away. Let me clarify, "food aggression" is classified as fighting for food. A dog that simply snarls, shows teeth, or growls is simply saying, "Back off, this is mine." There are plenty of dogs that bluff a good game, but will not actually fight for the food. This is because dogs often prefer to not have to fight unless they have too. However, you should never test your pooch. If your dog is showing any of these behaviors, consult your local trainer/behaviorist.
Another reason dogs fight, is for rank, or position, within the pack. Basically, there are some dogs that are more confident than others. These dogs display that they are willing to fight for things. They posture to show how big they are. They bare teeth to show how big and sharp they are. They growl to sound intimidating. These dogs are basically saying, "I am not afraid of you, and if we fight, I’m sure I’ll win." If this display works, meaning that the other dog submits, then they become higher in rank. If it does not work, however, then a fight will insue. Whomever wins the fight then becomes higher in rank. Dog fanciers call this behavior "T-ing up" which is when two dogs meet each other. During the "T-ing up" process, the two dogs will go through a ritual of either posturing as mentioned above, or submitting, which is when a dog lowers and curves him or herself. Now, it is important to keep in mind that dogs don’t think of rank in the same way that we do. Dogs are much more primative than us humans. Rank to dogs simply means that whomever is the most confident is at the top, and whomever is the least confident is at the bottom.
Dogs will also fight to protect their territory. Some dogs are more territorial than others, meaning that they will fight practically anything that steps foot on their land. In the wild, territory is very important. It keeps rival packs at bay so there is no or less competetion for food and other resources. In the home, it works the same way, but on a much smaller scale. Fighting for territory not only keeps rival dogs out, but also other predators, which can include humans, that might eat puppies or steal food or shelter. Dogs will always give a warning before fighting for territory, unless they are caught off guard, or taught not too. These warnings include, growling, raised hackles, curled lips, forward ears, standing on tip toes, a territorial bark, lower pitched howling, ect.
Resource guarding is another big reason why dogs fight. It is the same as "food aggression" but instead of food, the dog is willing to fight for other resources… hence the name. Resources can include, people, toys, bones, beds, or anything else that the dog sees as valuable. Think of resource guarding as a way to keep other beings away from your stuff. Dogs that have obsessions with guarding their resources have most likely had something valuable taken from them as a puppy repeatedly and they’ve learned they can keep it by displaying this type of behavior. So if dog A is bonded to you (leaning on you, pushing into your arms, laying on your lap) and dog B comes up for a nice scratch, dog A would attack dog B. This is resource guarding. (If you are also the leader of your pack, then dog A could also be showing that he/she is higher ranking than dog B). Dog B can then choose to fight dog A for you (the resource), flee from dog A, avoid dog A, or submit to dog A. If dog B deems that you are a valuable enough resource, he may choose to fight.
Once in awhile there is a dog born with an innate aggressive tendancy. And, there are people in the world that breed these dogs to other dogs like them, creating very aggressive dogs. They then use these dogs as fighting dogs to make a profit. In these types of situations, the dogs are not usually fighting for rank, toys, food, or anything else for that matter. They are simply bred to fight. Other dogs in these kinds of situations whom have not specifically been bred to fight, will fight to live. Life is the most highest ranking resource there is to any creature, including dogs. So if he/she must, a dog will fight for survival. Even nervous, scared, and weak dogs will fight to live. Fear aggression is very common in dogs, and is often mistaken for pure aggression. Fear aggression is displayed much differently than pure aggression though. Dogs displaying this type of aggression are often curved, lowered, and backed into a corner. They are saying, "I really don’t want to fight, but I will if you push me, or if I have too." Dogs that fight out of fear, often keep the fight as short as possible attacking with quick bites and nips. This is obviously because they do not want to be in the fight in the first place. Dogs displaying pure aggression are very postured. They raise their hackles, lift their ears forward, lock on to their targets, and don’t hesitate to attack. They attack with ferocity and don’t let up. A dog displaying pure aggression intends to kill his/her target.
These are some of the main reasons dogs fight. Every dog is different and may fight for different reasons. If your dog is fighting often, then you need to see your local canine behaviorist, or qualified trainer. You may also want your vet to do a check up to rule out any injuries or conditions that would cause your dog to fight more often.