Fur Loss

I adopted 2 chinchillas, Ben and Jerry, about a month ago. Ben is 4 and Jerry is 3, they have lived together the past 3 years.They have been getting along for the most part since the adoption. However, for the past couple days Jerry has been chasing Ben around during playtime and trying to hump him. This usually leads to some wrestling, never any serious fighting. Once this occurs I separate them into the top and bottom of their cage (feisty ferret). I have noticed Ben losing tufts of fur very frequently. I often find them in the cage and on myself after I play with him. After an episode of the chasing/ wrestling his fur looks as though he is priming with small patches sticking out. I think his back end is starting to look a little sparse. I am thinking the cause of all this fur loss is fur slip but it seems to occur very frequently. Is he losing the fur for another reason? Is there anything I can do to lessen the fur loss?

Ben also has had two spots of chewed fur on his flanks since adoption, these seem to be remaining about the same size.

No matter how long they have been together chins can decide one day to no longer want to be friends. I suggest you separate them, and let them both chill out for a little while, like a week or so. Fur slipping is a defense, so it's a clear sign that the chin is feeling threatened. The idea is that whatever is trying to attack them gets a mouthful or handful of fur instead of flesh, so it's a warning sign if that is happening with your two. Fur chewing can also be a sign of stress, so that's another warning sign things aren't good. Fighting can start as simple chasing, leading to pulled fur and fur slips, but can quickly progress to actual biting and killing. Obviously you want them to calm down before it ever gets to the killing stage. Take away the cause of the stress and the fur slipping, and possibly even the fur chewing should stop.

After some time apart try a playtime first, see how it goes, and progress from there.

Other causes of fur loss that I can think of that aren't fur chewing or fur slips, don't really fit your situation. Things like ringworm, which causes itchiness and fur loss normally starting on the face, and malo, which causes fur loss on the chin and arms due to constant drooling.

I would also just double check that they are both males too, just because they have been together for a few years with no kits doesn't mean they aren't male and female. Fighting can occur because the male wants to mate and the female doesn't. Though the humping could also just be two males trying to re establish dominance, if one decided he wants to be boss now instead of the other.