To determine which alternative would NOT be acceptable, we would need to see the specific alternatives provided for the underlined portion (i.e., the phrases “bird carrier” or “ironfish”). Since you did not provide specific options, I can guide you on how to evaluate alternatives.
An unacceptable alternative would typically either misinterpret the original meaning, use incorrect terminology, or introduce an element that doesn't accurately describe the original words in the original context.
If you provide the specific alternatives you're considering, I'd be happy to help you determine which one might not be acceptable!