The adjective phrase 'amazingly rare' modifies the word 'bird'.
Why?
An adjective is a single word that describes a noun.
A noun is a person, place, or thing. This includes animals. :)
A phrase has more than one word in it.
Adjective + phrase = more than one words used together to describe a noun.
In this case, the 'bird' is the noun being described.
The bird is modified in our understanding. It's not just any bird. It's an amazingly rare one.
