I would bet they never really were "his". That may be why he wasn't keeping up. Possibly the original herd bull got whacked, and the little guy tried to become the big guy. I have watched that behavior in pronghorn. Any satellite buck or bull had better try to get his job done fast, 'cause he is not going to keep a harem long. When that happens with pronghorn - the herd buck being whacked - those does bust out pretty quick and make an escape. They are always followed by whatever satellite bucks are hanging around the edges.
Be an interesting study if one had enough time.
