Quick Question

[Stefan-A]

Isn't the term intergrade intended to be used specifically to describe naturally and frequently occurring hybrids in areas where one subspecies gradually transitions into another?

ps. hybrid:
1 : an offspring of two animals or plants of different races, breeds, varieties, species, or genera

[Cazador]

Isn't the term intergrade intended to be used specifically to describe naturally and frequently occurring hybrids in areas where one subspecies gradually transitions into another?

ps. hybrid:
1 : an offspring of two animals or plants of different races, breeds, varieties, species, or genera

A "zone of hybridization" would fit the definition that you mentioned above, but a "zone of intergradation" would apply to the area in the wild where different subspecies interbreed.

Not sure where you got the definition of hybrid, but it sounds like a colloquialism, rather than a biological definition.