Green’s Dictionary of Slang

bird’s-nesting n.

womanizing.

1772		G. Stevens ‘The Sentiment Song’ in Songs Comic and Satyrical 125: Here’s the Nest in that bush, and the Bird-nesting lover.
1782		‘The Sentiment Song’ in Farmer Merry Songs and Ballads (1897) II 226: [as cit. 1772].
1909		Farmer & Henley Sl. and Its Analogues I (rev. edn) 228/1: to go birdnesting, to whore.