You are correct to draw a distinction between an animal yawning when tired and an animal yawning not through tiredness. Yawning in mammals increases the flow of oxygen to the brain and increases the heart-rate. All mammals can be seen yawning under nearly any circumstance, not just when they are tired or bored. In fact, because of the physiological impact of a yawn, some researchers believe that a yawn is used as a way to prepare the body for impending action. For example, many dogs that compete in agility competitions are seen yawning on the starting line, as if they are excited by the impending start and are giving their body an extra physiological boost prior to start. Similarly, a stressed dog can frequently yawn, as if they are maintaining readiness for unpredictable events – many dogs frequently yawn during obedience classes where they find the environment challenging and perhaps stressful.

As you suggested, your dog is, in a sense, trying to communicate something to you. My suggestion is that your dog is slightly anxious about something, probably something that he can not control and is unpredictable. Have you been re-decorating recently? Have strangers been coming and going from your home recently? Are you anxious about something? A change in your behavior or relaxation levels may also make your dog anxious. Finally, perhaps a cat or another dog is sometimes, but not always, visible from a window or from your garden and your dog has perceived the animal as a territorial threat. The best thing you can do, assuming there are no other physical symptoms, is to make sure that your dog’s environment provides routine, continuity and plenty of reassurance.