There are a lot of phrases, mostly old, in which a particular sort of person or thing is given a name, usually John or Jack, eg Jack Tar, John Barleycorn, Jack the Lad, John Thomas and Johnny Reb. At http://www.etymonline.com/index.php?l=j&p=0 it
says of Jack: 'As a generic name addressed to an unknown stranger, it is attested from 1889 in Amer.Eng. Used especially of sailors (1659; Jack-tar is from 1781.' I assume that Johnny Foreigner is similar.
It used to be done too with birds, and these nicknames have often got muddled with the original birds' names. For example:
Redbreast became Robin Redbreast, then just robin.
Daw became Jack Daw.
Wren became Jenny Wren (but then usually just wren again).
Pie became Mag(gie) Pie.
Tomtit too (am I allowed that one, AB?). In case not, Tom T*t.
I think not Kitty Wake though, nor Will O'Warbler.