To these I may add the origin assigned to the saying by Mr. Bellenden
Ker, in his _Essay on the Archaeology of our Popular Phrases and Nursery
Rhymes_, 1837, vol. i. p. 63., viz.:--
"A LITTLE BIRD.
"A good humoured way of replying to, _who told you this story?_
And imparting you don't mean to inform him, that you have a good
reason for not letting him know. _Er lij t'el baerd_; q. e. _by so
doing_ [telling] _I should betray_ [do wrong to] _another_," &c.