I have a cat. It's 8 months old. I decided to put a female in the house. She is his age. Both are neutered. Ever since the female arrived she has been trying to hide. I need to put her in a room but she keeps hiding under the sofa where neither I nor my cat can get to her. She hasn't been eating nor drinking. I'm really struggling... please give me some tips.
Initial shyness is normal.
Cats often rely on knowing their environment. Bringing them to a new environment will have them on edge until they find their bearings.
But more importantly, cats are territorial animals. Your new cat will definitely smell your first cat. Add onto it that it's a male (they can smell the difference), and that strongly incentivizes the new cat to not want to intrude on the other cat's territory.
Provide a safe space.
It's too late for that now, but you should have prepared this room before her arrival, and only set her free in the room.
Upon arriving, you should put the new cat in a separate room, all by themselves. You can visit her regularly so she gets used to you, but if she's not taking to you yet, don't overly intrude on her safe space. Just be there to give food, so they know that you mean well (since you give them what they need). Don't force them to interact with you, simply have them tolerate your (distant) presence as they eat. You can try to get them to eat closer to you day by day if they're still willling to.
Note that this room should have hiding spaces, but try to avoid any hiding spaces which you cannot reach when you need to reach the cat. I use cardboard boxes for this.
Ideally, provide amenities (litter box, water bowl, blankets, toys, hiding spaces such as cardboard boxes, ...) that have not yet been used by the previous cat. The idea is to remove the other cat's smell as best as you can. You can't negate it but you should try to at least minimize it.
Depending on the cat, this can take days or weeks. If she's getting her bearings, you can visit more frequently, see if she's interested in interacting with you.
Over time, you can start swapping out blankets/toys between the cats. This familiarizes them with each other's smell, without yet having to deal with the other cat directly.
When all those boxes are ticked, you can let the new cat come out if it chooses to. How you approach this strongly depends on how your cats behave:
- If he is interested and enters the safe space, and she is not into it, then you need to stop this from happening.
- If he enters the safe space and she doesn't make a fuss, neither should you.
- If they are both apprehensive of crossing the threshold and interacting, you can simply leave the door open so they get acquainted by seeing each other at a distance.
- If she's eager to explore outside of the safe space and he's less than welcoming to her, you temporarily remove him from the equation (put him in a room of his own). This has a double benefit: she gets to explore the house without interference, and he is punished for being unwelcoming to the newcomer.
- If either of them show repeated aggression, that means they're going to need training. That's a whole new chapter that I'm not going to go in here. It will require changing their behavior which is not an easy thing to achieve with cats (compared to dogs).
- However, don't mistake a single aggressive response (which may come from a feeling of needing to defend yourself) with a consistent pattern of aggression. It only becomes a problem if either party refuses to let go of the aggression in the long term.
Do not (initially) worry about not eating/drinking.
It's very possible that she is consciously deciding to not bother with drink/food because she's rather not run into the other cat.
More often than not, you can wait this out. Eventually, they will be hungry enough to change their initial decision (it's like how a child won't eat their vegetables but a starving man will happily eat anything that remotely looks like food).
If it becomes a medical problem (malnutrition), you need to address this. The safe space should preclude her reasons for not wanting to eat/drink; she should figure out relatively quickly that she can safely walk around in the safe space.
If she still refuses to eat/drink in a safe space, then it's time to take her to the vet. This can be indicative of a medical problem, or maybe she is in shock from having to live in a new and unknown environment. Don't guess, have a vet give her a checkup. At an absolute minimum, the vet can provide the needed hydration/nutrients to give the cat more time to find her bearings in your house.
Also, if she doesn't like going to the vet, she may realize she likes your house more than she initially thought - simply by merit of it not being as bad as being at the vet.