A couple other semi-related things:
First, the human siegers flee from my dwarves, although they will use bows if they have them. Looks like they're using the civilian AI that hunters use concerning battle.
Second, cage traps catch the mount, but not the rider. Seems like they should catch both.
You gotta love that groundhog swimming pool, though XD I imagine that the mommy pathed into the pool when it was half full, and then it dried up. Why they didn't try to path out of it when the pool began filling up again (though it never made it all the way before the dry season hit again) is a good question.