Rabbits tend to grieve in their own ways, and they often know something is up before we do. Sometimes a bonded mate will even abandon the other bunny in the final hours (which is heartbreaking to watch, but you can imagine why this would happen in wild bunnies). It’s good that he’s eating and drinking and zooming a bit.
One of my bridge bunnies, Bertha, was widowed a whopping 3 times. She always handled it well. I felt like maybe she was a bit quieter than usual, but it’s hard to tell what I was projecting from my own emotions, since I was mourning as well. I also noticed that after a few weeks, she got quite a bit more destructive. Not sure if it was grief or boredom, but I eventually rebonded her after each time.
You are doing the right thing by spending time with him and just letting him come to you. If he seems very lonely, you can try getting him a stuffy to cuddle with. Not all buns are into them, but some will cuddle and groom them.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.