Green’s Dictionary of Slang

birdie n.3

[play on SE peck, a perfunctory kiss]

(Irish) a kiss.

[US]J. O’Connor Come Day – Go Day (1984) 19: I’ll give you a great big birdie.
[Ire](con. 1950s) C. Kenneally Maura’s Boy 18: Will you look at the white head on him. Hello, blondie, will you give us a birdie?