Quickly, we realized there were few elk, and later no elk due to the harsh environment, so Mollie's pack wolves had adapted to eating only bison in the winter. Quickly the story became about wolves and bison. Formidable prey compared to elk, killing bison presented a different challenge to the wolves. Several bison kills were witnessed, and a few were filmed, wetting the appetite to learn more and how their strategy differed from killing elk. Bison commonly stand their ground, whereas elk commonly flee–a major difference we noticed right away. Wolves facing a 1,000-2,000 pound animal presented a unique set of problems; taking the bison head on was out of the question. Wolves would have to work the environment to their advantage. Watching and waiting for the right moment to attack was critical. Wolves seem to have all the time in the world, so they were never in a hurry and waited. When they decided to attack, they chipped away: attack, wound, and wait; attack, wound, and wait...Using this strategy, some kills took up to nine hours. The wolves also had to use terrain to their advantage. Wind-blown hills had no snow and the bison favored such terrain for better footing; between the hills were troughs that collected snow, so the wolves favored these areas for attack as the snow hampered bison defense.