The song of a Moustached Flowerpiercer is musical, though rather patternless, and consists of a series of fast, sweet notes that rise and fall erratically (Ridgely and Tudor 2009). The song can have 4-5 notes per second and last up to a few minutes long (Hilty 2011). D. mystacalis can usually be heard at dawn, singing from the tops of bushes or inconspicuous perches in trees (Hilty 2011, Fjeldså and Krabbe 1990). The song has been compared to that of a Citrine Warbler, except the high volume is consistent from start to finish (Isler and Isler 1987). The call is less heard, but can be described as a series of short, high “ti” sounds (Schulenberg et al. 2007). Additional audio recordings of vocalizations of Diglossa mystacalis can be heard at Macaulay Library and at xeno-canto.