Deffinitions of hybrids change to often.. Even dictionary deffinitions vary..
Mayr (1963) described hybridization as the
crossing of individuals belonging to two unlike natural populations that have secondarily
come into contact. (I.E. Breeder's)
Sibley (2000) Hybrids are the offspring of parents of two different species.
The offspring of parents of two different subspecies (of the same species) are know as
intergrades rather than hybrids.
Who to follow.. However since noone tends to agree on what constitutes a species ( Species change, ssp. change ) Making a former hybrid possibly a hybrid no longer, or into a different hybrid mixture.
Being said, I will stick to the simple Hybrids are a man's intervention and intergrades are a naturally occuring phenomenon deffinition. Matter of choice.