The authors agree that Birtig is a Friulian-Slovene surname derived from the dialectal Slovene term birt ("tavern-keeper, innkeeper"), taken in turn from the German Wirt.

E. Rossoni describes it as very rare, typical of the Pulfero and San Pietro al Natisone area, in the Udine area. He derives it from the German term wirt ("innkeeper") or, more probably, from the dialectal Slovene term birt ("tavern-keeper, innkeeper"). He documents traces of the surname in the area from the second half of the 16th century.

B. Zuanella presents it as a surname formerly typical of the village of Erbezzo, according to the baptismal books of San Pietro. From Erbezzo it probably descended to Podvarschis and by 1662 it was also present in Mersino. In the 17th-century parish books both the patronymic form Birtig and the form Birt are recorded. In Podar di Vernassino it was already present from the mid-17th century; from there it descended to Costa, Vernassino and Savogna (in the Podar locality). In Mezzana it is documented at least from the mid-17th century: on 18/2/1661 Cancianus Birtig married Fusca Scuria, of Ponteacco; on 8/6/1695, Casparus Birtig with Agnese Mansin, of Pulfero; on 5/2/1730, Giuseppe Birtigh with Caterina Blasutigh, of Vernassino; and on 25/1/1769, Gregorio Birtig with a Filia Marina, also of Vernassino. From Mezzana it then descended to Ponteacco and Brischis. The Birtig surname of Tuomaz di Rodda, to which Mons. Valentino Birtig belonged, comes from Podar di Vernassino. Zuanella confirms that it derives from the dialectal Slovene noun birt —taken in turn from the German Wirt, "tavern-keeper"—, so that Birtič/Birtig means "son of the tavern-keeper". He also recalls that the word birt entered the Slovene dialects very early.