Well, the chicken's mother would have been a chicken. The difference between the two organisms would be the same difference between you and your mother, practically no difference, other than your gender. Nothing species changing. When we talk about evolution we're talking about thousands of extremely minor changes, one after another, that accumulate after thousands of years to create a different species, but the before and after are only different when the after is compared to a before that lived long ago, not when compared to a before that is its direct relative.

It's like this: who you are right now is basically the same as who you will be tomorrow. But who you will be next year is very different from who you are now, not necessarily because you suddenly woke up one day and said "I'm fucking different as hell today," (which is possible, but it doesn't happen very much.) but because you changed in unnoticeably small increments. As a large amount of days bearing unnoticeably small increments combine to form a year, those small increments also combine to form a drastic difference.

It all just depends on what you're comparing on the line. When comparing offspring and progenitors, they will almost always be the same species, but when comparing an organism that is indirectly related to one that lived several thousand years ago, they will almost always be different species.

So, kind of, yeah, what Neil said. It depends on where you draw the line between chicken and protobird.