How did the terms ;birdie; and ;eagle; come into golf?
The term ;birdie; originated in the United States in 1899. H.B. Martin;s Fifty Years of American Golf contains an account of a foursomes match played at the Atlantic City (N.J.) CC. One of the players, Ab Smith relates, "My ball... came to rest within six inches of the cup. I said ;That was a bird of a shot... I suggest that when one of us plays a hole in one under par he receives double compensation.; The other two agreed and we began right away, just as soon as the next one came, to call it a ;birdie." In 19th-century American slang, ;bird; referred to anyone or anything excellent or wonderful.

By analogy with ;birdie,; the term ;eagle; soon thereafter became common to refer to a score one better than a ;bird.; Also by analogy, the term ;albatross; stands for double eagle;an even bigger eagle!