Your dogs hackles up is not a body language but it is a behavior that causes much concern and confusion among doggie folk. Hair doesn’t talk yet it does tell the emotional state of a dog. The medical term for the hackles going up is piloerection. Pilo refers to ‘hair’ in medical terms. So, when a dog’s hackles go up although it is a form of communication, it is communicating a state of being and is an involuntary reflex triggered by an unknown sudden occurrence putting a dog in a state of arousal. It communicates arousal and can mean that the dog is afraid, excited, unsure, nervous or angry. One must look at the rest of the body parts talking and the context in which this is happening so that you can understand and evaluate what is going on and only then can you know how to respond.
The hackles can go up just at the shoulders but if a dog is highly aroused the hair can stand up from their neck all the way down to the tip of their tail. Please don’t confuse the hackles going up with aggression. This confusion at a time of such arousal in a dog could be what turns a fearful dog into an aggressive dog in an instant as aggression is a fear based behavior.