"Eagle" is about becoming an American citizen.
Out of all birds, they picked an eagle. Out of all types of eagles, they portrayed a bald eagle- which is not even found in Europe, yet it is the national animal of the United States of America. The first half is about the singer's wish to be an American- "and I dream I'm an eagle"; while the second half is about the singer having become a citizen- "is it true I'm an eagle?". So while it can be taken literally, it can also be about becoming an American citizen with all the freedom and power it grants."Mamma Mia" is about a relapse.
