The recording below is from a male spinebill, head held high with his punky little crest up (which means he is either annoyed or randy I think, possibly both, if I reflect on personal experience).
I have no idea of how to differentiate between male and female spinebills other than through moments like this when males are clearly in the business of giving a stirring performance for the ladies (and to overwhelm probably rival males). It amuses me greatly that such a gentle and otherwise demure little bird tries so hard to appear the tough guy. If you’ve ever had the pleasure of holding a spinebill in the hand (say, if one flies into a window) you’ll know that there’s hardly a creature on this wonderful planet that’s more capable of melting a human heart.