15 year old spayed female urinating/defecating on bathroom rug at night only
Our 15 year female cat began using the bathroom rug for her night time potty. She has 2 litter boxes that we try to keep clean. During the day she uses the boxes with no problem.
My thoughts: I'm sorry to hear that your kitty is having problems. I would ask myself why her night time behavior would be different from day time.
In other words, what is different about the box (or your cat's condition) at night?
Obviously, cleaning the boxes in the evening would be a good test to see if box cleanliness is a problem. Has her routine, or the routine of anyone in the house changed just prior to the start of the problem?
Given the age of your cat, I wouldn't rule out a medical condition. For example, failing eyesight may mean that it's difficult for her to use the box at night.
You might try leaving the lights on where the boxes are for a couple of nights and see if things change.
Older cats can also develop dementia. The symptoms of dementia can be worse at night, and one of those symptoms is failure to use the litter box, presumably due to confusion or forgetting litter box training altogether.
You might want to stay up with her all night to observe her behavior. This may help you understand what's going on.
There are other medical conditions that may be at work here, and any major behavioral change can be an indication of illness.
Based on that, and your cat's age, I'd set up a vet visit. If she hasn't had a blood panel done recently, it's time.
Another possibility is that your house has visitors at night that don't come around during the day. There may be wild animals or stray cats coming into her territory and this is a response to that.
I hope that helps and please keep us updated on her progress.