Use of the 'bird' when referring to a young maiden [duplicate]

Oxford dictionary of Word Origins says that the British slang use of bird to mean a young woman is associated with 1960s and 1970s but as you mentioned also, it dates back to Middle Ages. It also adds that the Virgin Mary could be described in those days as "the blissful bird of grace." The modern use appears to be something of a revival.

OED also mentions that this sense of bird was confused with burde , burd n., originally a distinct word and in modern (revived) use, it is often used familiarly or disparagingly. It lists the first usage in 20th century from 1915 as below:

1915 P. MacGill Amateur Army v. 62 There's another bird there—and cawfee!

We might say that the modern usage is revived by media, especially starting from the below usage of News Chronicle article. [It was a British daily newspaper, later absorbed into the Daily Mail.]

1960 News Chron. 16 Feb. 6 Hundreds more geezers were taking their birds to ‘The Hostage’ and ‘Make me an Offer’.

Here, geezer is a British slang for a young lad, bloke (can be an equivalent of dude in AmE). "The Hostage" and "Make me an Offer" were the famous movies of that time.