Chihuahuas, like other dogs, howl as a form of vocal communication. Howling can be a cry for attention, a way for the dog to announce his presence or a form of communicating with others. Howling can also be a response to sounds, such as sirens on a passing emergency vehicle.
Dogs may howl when they are anxious about separation from their owners. They can also howl in response to the howling of other dogs. A dog may also howl to signal that he is sick or hurt. A dog that howls more than usual should be evaluated by a veterinarian as soon as possible to rule out illness or injury.