Per the "internet", the buffalo are running away from the Yellowstone Caldera. I have yet to see any corrobative statements. They might be feeling frisky and playing also.

Just because Yellowstone has produced three very large eruptions over the last 2.2 million years doesn’t mean that you should expect such an eruption. The caldera system has had plenty of smaller, dome-forming or explosive eruptions in the intervening years (and since the last caldera-forming eruption; see above), so in terms of the likeliest events, that is what to expect. In the paper by Guillaume Girard and John Stix in GSA Today, they suggest that the likeliest events to happen at Yellowstone in the near future are small, dome-forming eruptions or phreato-magmatic (water-influenced) explosions that follow pre-existing faults in the caldera, especially along the western rim. In fact, another study by Christiansen and others (2007) showed that probabilistically, another caldera-forming eruption is the least likely scenario for future activity at Yellowstone.