Good advice. I hadn't thought of either of those things.Originally Posted by cloud_shade
There are two things that come to mind. First, he could be losing his site. If he can't see very well, he may be trying to locate you (or your other cat) based on your responses to him. Also, hyperthyroidism, which is common in older cats, can result in night-time yowling. A blood test would be helpful to determine whether he has hyperT (which is very treatable with medication).
That could go right along with cloud_shade's advice...maybe he's got a bit of night-blindness in his old age.Originally Posted by Purity
You could try leaving a night light on for him, maybe he doesn't like the dark in his old age?