Wondering why your grandfather Leib changed his name to Louis? or Aunt Blima was known as Rose?
My grandmother began life as Chaya Feiga, adopted Birdie and then Bertie as a young schoolgirl and was later known as Bertha. In Yiddish, Feiga means a bird, thus the connection to Birdie, Bertie and the more sophisticated -- for the times -- Bertha, is obvious.
In the large Persian community in Los Angeles -- so large that the city is called Irangeles or Tehrangeles -- Feridoun, Faramarz, Farid, Farajollah, Farhad, Farshid and other first names beginning with "F" are, in many cases, now simply Fred!
The New York Times had an interesting article, "As American as Vartan," about name changes among immigrants.
For a good look at how Jewish given names have changed as families immigrated to many countries, go to JewishGen's Given Name Database, compiled by Dr. Jerry Esterson.