MarkB
Legend
Reskin the "charming call" as a "hypnotic pattern" created by their effortless circling patterns in the air.
Ever seen a group of vultures homing in, circling at different levels, different directions, getting ready to descend on a found kill [or in this case, I guess, potential kill]? Add in magic and I'd definitely say that could be mesmerizing.
Make it a bit of both, and you get something like this.
[video=youtube;bja8UUtZRls]https://www.youtube.com/watch?v=bja8UUtZRls[/video]