why the dog barking in night only

Your dog is older and he may be suffering from dimensia, altheimers, or there may be something physically or outside irritating him. Dogs have MUCH better hearing and sense of smell than we do, and he may be hearing or smelling something that you can't. Take him to the vet to make sure there are no physical problems, such as arthritis, that is causing him pain. He may also be bored at night. Give him a busy bone or a KONG to keep him occupied. You may even want to play a CD with noises of the daytime on it. If your computer has a cd-rw drive and a microphone, leave it on record and then save the file and loop it so that it fills up the cd. Then, at night, put the CD on in the room your dog is. This may help him settle down.

Because they see ghost at that time only :-)