if you are not using locaters you are loosing a lot of rabbits. sometimes a ferret can back up 3 or 4 rabbits in a stop and without a locator you wouldnt be able to get them out
how do you know the ferret has killed underground ,fur on the claws only indicates a ferret scratching a rabbit try a locator and you will find most of the rabbits are alive your ferrets may be quitters and only by digging can you be sure of a kill
steve