Ok, so my fortress, like many others has an animal problem. My solution to this was to dig a 4 z level shaft with a retracting bridge on top. Surround the bridge with walls with 1 door set to forbid but not closed tight. I placed a meeting area on top and when my unwanted manageree assembled I pulled a lever dropping them into a refuse stockpile. At the bottom I surveyed the carnage with glee.
I was however saddened when the butcher told me that there no butcherable, unrotten meat nearby. This is annoying to me but I will not give up. I try removing the refuse pile, no joy. I try removing the wall between the butcher and the refuse pile, no joy. I try moving the butcher closer, no joy.
Finally in exasperation I try to drop the corpses straight into the butcher's shop. Finally joy. Though not the kind I was hoping for. I got the message that a cow (tame) has died in a collision but also my butcher had died in a collision. Once I stopped laughing and picked myself up off the floor I realized that this could have military applications.
The entrance to my fortress is over looked by a cliff. I am hoping to put a drawbridge that will fling the hapless creatures off the cliff onto the haplesser invaders.
This raises some questions. First will this work? Second how far should I be expecting the range of this contraption to be. I am willing to make the bridge fairly large and fling a nice scattering of animals all at once. Third What all will be taken into account in the range the creatures fly? Does the position on the bridge and relative weights of the creatures matter?
For bonus points is there a way I can butcher the resultant carcasses?
I also just realized that since my murder tower opened to above ground it was technically outside. Could this have had anything to do with my butchers reticence to gather the corpses?
Sorry for the wall of text if you have made it this far.