C18: perhaps related to Old English beorcan to bark; compare Old Norse berkia
birkie in American English
(ˈbɜːrki, Scot ˈbɪʀki)
noun
Scot
an aggressive, independent man
Word origin
[1715–25; of uncert. orig.]This word is first recorded in the period 1715–25. Other words that entered Englishat around the same time include: blackleg, dugout, hallmark, leverage, screening