The Collaborative International Dictionary of English v.0.48:

Birdie \Bird"ie\, n.
   A pretty or dear little bird; -- a pet name. --Tennyson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

birdie
    n 1: (golf) a score of one stroke under par on a hole
    2: badminton equipment consisting of a ball of cork or rubber
       with a crown of feathers [syn: shuttlecock, bird,
       birdie, shuttle]
    v 1: shoot in one stroke under par