"to emit a shrill sound," mid-15c., probably from a Scandinavian source (compare Norwegian dialectal skrylla, skrella "to shriek"), ultimately of imitative origin. Originally of persons, in reference to bagpipes it is attested by 1660s ("Baith skirl and screed") but now rarely is used otherwise. Related: Skirled; skirling.
As a noun, "a skirling noise," 1510s, from the verb. Compare Middle English skrillen "to shriek, scream" (late 15c.) also probably from Old Norse.