It does not mean the carrying capacity of the land has been exceeded, not even close.
It means more horses than allowed by plan, too many resources lost to animals that bring in no economic return.
The resources are there. In most cases there are no ‘excess’ horses. There is no basis for a roundup or fertility control program. Most of the ‘advocacy’ groups are clueless.
The problem is resource management—the plans—which typically allocate four to five times as much food to privately owned livestock as they do to wild horses, on lands identified for the horses.