A birl is a musical ornament that is used by Scottish pipers. It is similar to the ornament that is called a "turn" by musicians who play other instruments.

Birling is also the chorus of this famous Canadian NFB animated short, the Log Driver's Waltz:

http://www.youtube.com/watch?v=0ekqsHP9Sck

"And he goes birling down & down white water/that's where the log driver learns to step lightly..."

I never knew it was a real English word, I always just assumed it was Northern Ontario slang!

Bill: this?

Kinda hard to tell from a still photo. In pipe music there is no easy way to separate individual notes if they are the same note as a preceding or following note. To get over this problem the piper produces a series of grace notes that can get fairly complex. Check here for a tutorial

In piping the birl is a rapid double touch on the lowest chanter hole with the little finger of the right hand. It's kind of onomatopoeic really.