Cat Pooping on Concrete Basement Floor

I have three cats, 17, 8 and 7 years old. We have 3 litter boxes in the unfinished basement that they have always used. However, for the last three weeks one of the cats (don't know which one) has been pooping on the concrete floor in a different area of the basement from where the litter boxes are. I don't know why this is happening. There have been no changes in our home. It's disgusting. Help!

Answer by Kate
The only thing I can suggest is that the basement smells new and different to any usual smells and the pooping is the cats way to mark the new territory and make it smell more like theirs. This is a normal cat behavior and usually subsides once the cat has got used to the new thing in the home.
Also make sure the litter trays are not to close to each other as the smell of other cats mess can also disturb a cat into this sort of behavior.

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