An alternative question is, “Why does my cat put her bum in the air?” Let me describe what happens and why it happens. Your cat comes onto your lap and you stroke (pet) her back from the center down towards her tail. You do it a few times and each time she raises her back upwards against your hand. The action varies between cats and as your hand approaches the tail your cat raises her bum in the air further. It’s quite noticeable and it looks a bit strange.
The reason why cats do this
Domestic cats behave as kittens in our presence. They view us as surrogate mothers and they are held in an emotional state of being a kitten. When a kitten is under three weeks of age their real feline mother has to stimulate urination and defecation by licking their bum. This behaviour is called anogenital stimulation.
Mother cats have to do this to ensure that their kittens urinate and defecate but it is no longer necessary after three weeks when kittens begin to move away from their sleeping area for elimination of urine and poop.
Cats raise their bottoms to facilitate their mother’s anogenital stimulation. It is a neonatal reflex action by the kitten. It’s instinctive and is carried out automatically. Our adult cats do it with their human caregivers because mentally they are cast back to when they were young kittens because petting is like a mother licking their kitten which triggers the neonatal reflex to raise the bum so their mother can lick it.
Google finds one website, and places it at the top of their search results, which purports to explain this behaviour but in my opinion they are incorrect. The website says that cats do it to increase pressure on their backs and to transfer their scent but this is incorrect in my honest opinion. The real reason as mentioned is far more subtle and rooted in instinctive, natural feline behaviours.
Breeders taking the role of mother and performing anogenital stimulation
Sometimes cat breeders take the role of a kitten’s mother and wipe the kitten’s bum as you can see in the videos below. One is of Martin Stucki who used to own A1 Savannahs with his wife Kathryn. The kittens that he is handling are super high quality F2 Savannah cats as I recall. They are very noisy and adorable. It begs the question as to why Martin did not leave the kittens with their genuine mother to take on this role of anogenital stimulation. I don’t know the answer to that. The other video is the Kitten Lady.
Other neonatal reflexes
For the sake of completeness, another neonatal reflex behaviour is when kittens become limp when their mother picks them up by the scruff of their neck. We all know this one partly because it’s been popularised on television and you see lots of videos of this on YouTube. When a mother picks up their kittens by the scruff of the neck in their mouth the kitten becomes limp which enables the mother to carry their kitten to a new den without their kitten struggling and interfering with the task. Mothers will take their kittens to a new den in the interests of their safety and security.
Another neonatal reflex action is the “rooting reflex”. The mother licks their offspring and he or she wriggles in a swimming motion with the front legs as the back legs push forward towards their mother’s nipple. They locate the nipple when pulling the head back and opening their mouths. Each kitten of a litter becomes attached to their own nipple which results in harmony during feeding.
You can see that there are a lot of inherited instinctive actions that nature has bestowed upon the mother/kitten relationship to improve survival of the family.