Sources

Braonaidh: Diack Place-names of Pictland, II, 167

Braonaigh: Watson in Diack

Birnie in Morayshire is ‘Brennach’ before 1200, which is simply G. braonach, a moist place; the dative-locative is braonaigh, which becomes Birnie in Scots by the usual metathesis. Watson 1926, 189

“Brennach, therefore, may safely be taken to represent Braonach, locative Braonaigh, whence in modern Scots vernacular Birnie, meaning ‘(at) damp place’”: Watson Topographical Varia, 1913