I've found nothing on "little yorkla harlin," but here's an interesting rhyme about the "yellow yorlin" (yellowhammer):

Newcastle Weekly Chronicle (Newcastle-on-Tyne) (May 25, 1889), p. 8:

"In the writer's schoolboy days, there was a rhyme supposed to be descriptive of the evil propensities of this handsome and harmless bird. It was something to the effect that

    The yellow yorlin
    Drinks a drap o' the de'il's bluid every May morning."