I'm not convinced that they howl at the moon at all. Wolves howl to communicate two main things: "We own this territory." and "Where are you? I'm here." So they're really howling at each other. Howling carries over long distances and the sound of the howl tells other wolves the size and number of wolves holding a territory. Wolves may even be able to recognize each other's voices.

They do tend to howl more as darkness is falling, or morning is coming. That might be why people think they're howling at the moon. They also tip their heads back, adding to that impression.

Dogs still have some wolf behavior, so some howl. The only time my old dog ever howled was when we got separated in the woods. Then it helped us find each other. Some dogs howl at sirens. It's probably because the siren sounds like howling to them. Some are just bored.

What do you think the other sounds a wolf makes (barking, growling, yapping) mean? How might they communicate without making a sound? Do you know how to say "let's play" in canine?