My definition for the Kind, as I have oft pointed out, is that individuals of the same kind CAN produce offspring, not that they necessarily will in nature. The issue here is genetics - the actual ability of organisms to produce offspring - not behavior, which may determine whether two organisms in nature [i]will[/w] produce offspring, but say nothing about whether they can or can't.
It's true that Mayr does make that distinction; But as commonly applied, species refers only to those populations that do interbreed, not those that might. Jackals and wolves may be able to interbeed, lions and lynx may be able to interbreed, but no one to my knowledge would call or even think of these organisms as belonging to the same species, respectively. Practically speaking, the concept of species strictly refers to those populations that do interbeed.