Elephants are reputed to have long memories and children’s books have many examples. Dogs have a reputation of short recall and a “live for today” attitude to life. I am not convinced of this.
A few years ago we ran kennels. Two dogs from separate homes were placed in adjacent pens separated by wire fencing. From day one they perpetually argued through the fencing so we separated them, but they could see one another even though they were a good distance apart. We moved them so they could not see one another. The arguments reduced but still continued until one dog went home. His enemy stayed and became calm.
Over the next few years each dog came to the kennels but never at the same time so the incident was history. However three years later one came and the following week the other arrived so they overlapped by four days. As soon as number two arrived by car, even before he had seen the other dog, the rumpus was started all over again and continued afresh. It was astonishing. In human terms I do not harbour grievances and if I have a heated argument with some one it is all forgotten if we meet even a few months later. That, however, is applying human behaviour to an animal. It is a mistake. What triggered off the second aggression? They had not even seen one another. Was it scent?
We had a dog of our own called Digger. Driving over a wild country area I came across a pony which had been knocked down by a car. I immobilised the pony which was attempting to get up thereby making his injuries worse and left a passing motorist to divert the scant traffic while I went to fetch the police and get a local vet. When we arrived at the police station a very short drive away I took Digger One into the station. On seeing a police officer in uniform Digger went berserk and became very aggressive. Totally out of character. Did the sight of a man in uniform trigger something in his memory bank? He had been our dog for six years. Who can tell?
I went to a store where dogs were not permitted with another dog, Jake, and tied him to a rail outside the shop where I could see him, it being too hot to leave him in the car. The shop owner asked me to move the car a few metres as she was expecting a delivery of goods. I moved the car about three metres but Jake went crazy. Did he think I was abandoning him as he once may have experienced? That must have been at least seven years before.
I believe dogs do have long memories, but memories of association. It is worth bearing in mind if your dog behaves out of character.