I got my two baby boys about three weeks ago. I am a first time chinchilla owner but I did extensive research before getting my boys so that I could be the best chin parent possible. We (my fiance and I) got ours from a hobby breeder and she said they were both boys and very healthy and even sociable. The first week we would just put our hands in their cage and pet them, then we started doing daily playtime where they are free to come in and out of their cage for at least an hour while we take 20-40 minute turns sitting in their play area with them, they climb on us and run around happily. They have both warmed up to us, but it took one longer. We have a tan one (Sala) and a med ebony one (Gimli). Gimli is supposed to be a month older than Sala but Sala looks significantly bigger. What worries me is the mounting behavior of Sala. At first he would only half heartedly mount his cagemate, something I knew could just been harmless dominance hierarchy building, but it was always a frequent thing. Gimli didn't seem too bothered by it, usually just ignoring him or just kind of walking away. But the last several days Sala has gotten more 'intense' about it. He mounts him and humps at him, making squeaking noises, Gimli's reactions haven't changed much but now we actually have to pull him off of Gimli instead of just kind of nudging him or saying something. They seem to get along despite all this, there has been no nipping or fur loss, but Sala keeps getting bigger than Gimli too. Gimli has always been more sociable, warming up to us faster and showing very little fear while Sala has always been more cautious, skittish and fearful, but both have warmed up to us now. Any ideas would be much appreciated.