Ref:A Dictionary of English Surnames, Oxford University Press 1997. Baird is not given as a variation of Beard.Baird is given in the Introduction to the dictionary under the heading 'SCOTTISH SURNAMES' and a subheading 'Clan-names' and a further subheading 'From Scttish places' (p.liii-lv). Beard is given in the main body of the dictionary as an English surname from Old English beard, frequently translated by French barbe. and often in prepositional form '(the man) with the beard' e.g the name 'Baldeuuinus cum barba' was recorded in Cambridgeshire in 1086; and 'Robert a la barbe' was recorded in 1178 in Buckinghamshire.
MY COMMENTS When people emigrated to the New World, some could not spell or write, and English scribes recorded their names as they heard them, hence corruptions of Bairds becoming Beard, etc.