The short answer is they’re communicating, but barking is only one part of the message—the rest is body language. A confident, dominant dog may bark at another dog approaching his property to advertise his presence and signal a warning—”Halt! Who goes there?”
As he barks this message, head will be held high, his eyes directed toward the other dog. Also, his ears will be pricked and forward (if possible), his body will be tense, his tail erect, and he may be walking forward. A more fearful dog being approached by another dog may bark a more furious and flamboyant message: “Stay away from me! I’m a force to be reckoned with, you know.” His body language gives away his fear—his eyes flicking furtively from side to side, his ears pressed to his head, his hackles raised, his rear end low, and tail held tucked. In moments of boldness, he may come forward a pace or two, then fearing he may have overstepped the limits, he may retreat to safety. The combination of barking, body language, and approach-avoidance behavior gives away the fearful dog’s motivation, even to us relatively uneducated body-language readers.
Barking alone is a relatively crude communication. If it means anything, it may mean, “Over here.” It certainly doesn’t communicate anything sophisticated like, “Hey you over there, it’s me. I’d really like to meet you. Come over to my house and we’ll see if we can’t get something going.”
Originally published in AKC Family Dog.