Kir- in this context is unclear; the word itself means 'cut', 'cleave', but those ideas hardly seem to fit the tiny kirinki, at least in a literal sense. Possibly the word is being used here in reference to the motion of their flight, or perhaps in the sense of 'piercing', in a metaphorical allusion to their high-pitched calls. The second element -rinki is probably derived from an old word meaning 'twitch, move quickly', which does indeed seem to match the typical behaviour of small wren-like birds (though it may also be connected from inkë, 'little').