A carpeted kitty condo, scratching post, or climbing pole may provide stimulation. A perch can be as modest as a square piece of plywood covered with carpeting. Brackets attach the perch to the window sill. A variety of commercially-made products are also available. Indoor cats can get pretty irritated with outdoor cats.
Abnormal behavior ranging from loud crying to destructive drape shredding can result.
Try to shield the indoor cats from the outdoors. Cover your windows. If outdoor cats are straying into your yard, contact the local humane society and make them aware of the problem. Dr. McCullough stresses that adding a new kitten or adult cat to a household where a cat or cats already reside takes time and effort to be successful. Adding a new kitten can cause an established indoor cat to behave badly.