a warbled song or succession of melodic trills, quavers, etc.
7.
the act of warbling.
Origin: 1300–50; Middle English werble a tune < Old North French < Germanic; compare Old High German werbel something that turns, equivalent to werb- (cognate with Old English hweorf- in hweorfan to turn) + -el noun suffix
c.1300, from O.N.Fr. werbler "to sing with trills and quavers," from Frank. *werbilon (cf. O.H.G. wirbil "whirlwind," Ger. Wirbel "whirl, whirlpool, tuning peg, vertebra," M.Du. wervelen "to turn, whirl"); see whirl. The noun meaning "tune, melody" is recorded from c.1300.