Can other supernatural species be influenced by a siren's song?
Good question! This is something we’ve given a lot of thought to. It all boils down to the victim and the siren, generally. Most supernatural creatures are able to resist the song; they will feel the pull of it, but they are able to fight it if they want to. The stronger the song and intent, the more difficult it is to resist but they still can. However, in some cases where the Siren is particularly powerful or the supernatural being is particularly weak, they can be easily overtaken.
The other side of this is that, yes, a Siren can and will feed from any supernatural being they can overtake. And if a being chooses to allow a Siren to influence them, for whatever reason, this too provides a feeding for the Siren. Unlike a human, supernatural creatures offer a Siren a lot more and can help sustain them for a longer period of time.
In Nightmare, they may be some agreements among folks that a Siren may feed on them. Otherwise, there is a set time every couple weeks that the Siren’s leave Nightmare to feed on humans in the nearest towns.