If you're doing the HOT Zone task/Quest to kill a harpy patroller, They spawn on the western most land mass. If you look at the map it's Next up to Harpy Grove. I hope this helps. I know it took me a sec to figure it out.
I see this site only mentions the stun DD but today after an update I started to get hit with a new spell along with the stun DD already mentioned. Here is the message I get in chat:
a harpy begins to cast a spell
Sinyr has fallen to the ground or you are no longer feigning death, because you moved
A powerful blow knocks you to the ground. You have taken 300 points of damage.