Birdie vs Willie

Birdie

name
  • A female given name from English. 

  • An effective or child's term for any (small) bird. (1999: Oxford Dictionary of Slang, p. 130) 

Willie

name
  • A diminutive of the female given name Wilhelmina or a feminine diminutive of William, often in the form Willie Mae. 

  • A diminutive of the male given name William 

How often have the words Birdie and Willie occurred in a corpus of books? (source: Google Ngram Viewer )