I would try to close the distance. Sounds like they are gearing up for the nights hunt and you are hearing a group yip howl. That is probably thier core area and spend most of thier time in that area which is good for you. If you can sneak in early and get set up no more than a coupl hundred yards that would be ideal. You are going to have to watch the wind while sneaking in. Try to keep it in your face and set up high on them if you can. Watch the down wind side and don't over call. If you don't see anything, sneak out the same way you snuck in, QUIET! Good Luck.............Tim