by Barbara George, Tellington Ttouch Behaviourist
When one cat from a multi-cat household has been away from home for a while the other cats in the family may not recognise him when he returns; this can cause non-recognition aggression.
Cats have many ways of identifying family members, mostly by smell but also by sight, sound, and behaviour. Differences may be caused by treatment, including shaving, stitches or amputation, wearing a cone or bandage, medicine, not grooming, or hormones that reflect stress or fear.
Being both predator and prey, safety in the home is important for cats. The cats at home do not recognise the in-coming cat and treat him as an invader, a threat to their territory and peace. This form of aggression appears to be most common where the cats were closely bonded, or where the stay-at-home cat is generally a loner or fearful by nature.
The first step in resolving the issue is to separate the cats and allow the resident cats to relax. The returning cat must be allowed to recover, preferably until bandages and/or cone is removed and he is grooming himself as normal.
Depending on the personality and behaviour of the cats, it may be possible to re-unite them at this point, otherwise they will need to be re-introduced as if the returning cat is a new-comer, with a change in the scent-swapping process
The returning cat may not be his normal, healthy self yet, or still be on medication that would influence his scent. Scent swapping is only done from the resident cats to the returning cat. This is to make him smell as the others, and to be accepted as one of the family again. An alternative to this would be to make all cats smell the same as the owner/main caregiver by rubbing all the cats with a sock worn by this person. This unites all the cats into one family.
Calming remedies can be useful for integrating previously-friendly cats; there are a number of natural ones available. If using a calming collar close observation is needed to determine which cat needs the collar, or if each should have one
After a few scent-swapping exercises an introduction can be attempted, based on the behaviour of the cats. For temporary separations this may be sufficient.
If an introduction does not work smoothly then separate the cats and do a complete re-introduction as for a new cat.
Meetings must be supervised until they are getting along. This can be tricky as we tend to be anxious about the meetings which causes the cats to be concerned and can have a negative impact on the outcome. Playing games with the cats at the same time at opposite sides of the same space is a good way to let them interact safely. Give the cats treats after the game and separate them before any negative interaction occurs.
The cats will settle into a routine that suits them. They may not be best-buddies initially, that usually comes later. In most cases, with patience and time, the cats are integrated and life returns to normal.