Rulings

Zhur-Taa Druid’s last ability isn’t a mana ability. It uses the stack and can be responded to.
Zhur-Taa Druid’s last ability doesn’t trigger if it becomes tapped for any other reason. However, if Zhur-Taa Druid gains another mana ability that requires you tap it, its ability will trigger.
If you tap Zhur-Taa Druid for mana during the process of casting a spell or activating an ability, its triggered ability will resolve before that spell or ability.