MISSOULA — Kidnapping a mounted moose head comes with challenges. Just ask the students in the University of Montana’s Alexander Blewett III School of Law. A group of law students snuck into the forestry building last week to steal Bertha, the mounted moose head hanging from the banister. The heist is a tradition that dates back to the 1930s and fuels a rivalry between UM’s law and forestry students.  “How many law students does it take to steal a moose,” joked Brandy Keesee. …The moose theft was not as rowdy as years ago, but as part of the tradition, the forestry students wait a few days and then retaliated by decorating the law school’s atrium with freshly cut fir trees. …The Bertha heist and retaliation are meant to kick off the Foresters’ Ball. This year’s 105th Foresters’ Ball will be held Feb. 2-3.