There is such a thing as overgrooming, and it is also known as “barbaring” – this is a response I compiled awhile ago because I actually had an over-grooming issue with my bonded pair. If the bald spot is causing an issue, there is also a section at the bottom on how to try to help Penny grow her hair back:
1) Sometimes barbaring is caused by stress. This can be reduced by giving your bunnies a very regular schedule, for example: feeding, cleaning, and giving them play time at around the same time each day.
2) Sometimes barbaring is caused by boredom. If your bunny has a particular toy he really likes to chew on, for example: cardboard or willow wood, provide a LOT of this for him to chew on and to play with. I gave my boy a couple big willow boxes (found them at IKEA!) and he has been having the time of his life chewing holes in them, and it keeps him distracted for a long time.
3) Sometimes barbaring can be caused by an irritation or bald spot on the skin. If your female had some type of irritation in her eye, it could have caused the male to start overgrooming, and now that there is a bald spot, he will become even more fixated on it.
4) Binkybunny found out that sometimes it is not enough fiber in the diet that can cause this. When I changed from one kind of hay to another that my boy bunny liked more, the barbaring stopped.
What to do now that there is a bald spot:
In order to prevent the male from continuing to fixate on this bald spot, you want to separate them for 2 or 3 days, just long enough for her to start growing some fur over the area. Then he won’t notice the bald spot so much and try to clean it. I did this by just using some NIC cubes to put down the middle of the cage, and put a make-shift litterbox on the side that didn’t have one. You want them to still be able to see each other, lay next to each other, and still be in the same cage because you don’t want to interrupt their bond. You don’t have to be very complex about it because its only for a short period of time.