As Howie's plane flies out, we hear Northumbrian pipes w/ 2 female singers (1 overdubbed harmony?) "Lesley Mackie [Daisy in the film] also sang the haunting credits/flight music and the Northumbrian pipes for that were played by Bruce Watson" (Gary Carpenter's site.)
According to Cinefantastique, this "is a piece of Gaelic mouth music..."
The lyrics are from a Robert Burns poem of the same name. Giovanni used verse 1 and 3, modifying verse 3 slightly.
Oh! I am come to the low countrie, Och-on, och-on, och-rie! Without a penny in my purse, To buy a meal to me.
And there I had three score o' yowes, Och-on, och-on, och-rie! Skipping on yon bonnie knowes, And casting woo' to me.
The second verse was changed to:
One time I had a hundred sheep
upon, upon a dream
skipping o’er your narrow creek
and growing old for me
1:57 (part of a medley)