Mating between different groups is not enough to deem them conspecific: those matings have to produce viable and fertile hybrids. And “viable and fertile” means not only that the hybrids can have offspring, but that they do have offspring in the wild. Some interspecific hybrids in birds, for example, are viable and fertile, but are not recognized as proper mates by members of either parental species because those hybrids look weird or have strange mating behaviors. That is a form of reproductive isolation, too: it’s analogous to sterility, but sterility on the grounds of not being attractive as a mate.