Similar to the Moaning Banshees. Hit up for 650 and AoE drain mana. They begin to sing a fire resistance song when Maestros HP hit around 25% which renders him practically immune to fire nukes (which he is very acceptable first), you'll get an appropriate yellow message when they start the song.
Kill them fast and if possible out of the range of the clerics or you might get spanked.
(Might mix them up with the Moaning ones but whatever :P)