Birdie vs Tiff

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) 

Tiff

name

  • A diminutive of the female given name Tiffany. 

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