Many people don't realize that animals grieve the loss of companions and family members. In other cases, people feel the thing to do is to rush out and find another pet so the grieving cat or dog is not lonely. Not acknowledging that animals grieve, or rushing out to find a replacement pet can have disastrous effects on the surviving pet.
Even if companion cats didn't get along, the surviving cat can still grieve. She's confused about where the other cat went. The two cats, regardless of whether they were close or not, had negotiated areas within the household such as who would sleep on the owner's bed or who got to eat first, etc. The surviving cat is left confused about whether to now risk crossing onto the other cat's turf.
The grieving cat also gets the double whammy grief effect when she sees her owner acting distraught. Cats are creatures of habit and they depend on their owners acting the same from day to day. As the owner grieves the loss of a pet, the household dynamic changes and the grieving cat picks up on the extremely elevated stress level.
In an effort to prevent the cat from being lonely, or to try to ease family members' pain, the owner may bring home another cat. This almost always ends in disaster. The grieving cat (and keep in mind that cats are territorial), is not emotionally ready to handle the intrusion of an unfamiliar animal in her home. As for the poor newcomer, he finds himself landing in totally hostile territory. New cat introductions take finesse under the best of circumstances so attempting to do it while one cat is grieving is just asking for failure.
If you've recently lost a family pet and you're concerned about your surviving cat, don't be in a rush to fill that empty space. Instead, what your cat needs is time with you in a casual, normal way. She doesn't need you to clutch her tightly and sob into her fur. All that will do is tell her that the bottom has dropped out of her world. She needs to know that much of her everyday life is still normal. She needs to be with you but she needs it in the form of lots of playtime, interaction with family members, petting, grooming, all the things you normally would do with her. At some point, later on down the road, you may decide that she would benefit from a companion cat or dog, but first take time for her to recover emotionally.
Watch your cat's eating and litter box habits as well. It's not unusual for a grieving cat to stop eating or to experience a change in litter box habits. If you notice either of these, contact your veterinarian. It's very dangerous for a cat to go two days without eating because of the very serious risk of liver damage.
For more information on helping your cat during the grieving process, or if you're at the point where you'd like to introduce a second cat, check out the book Cat vs Cat, or visit our website at www.catbehaviorassociates.com