How do grizzly bears and wolves in Yellowstone National Park carry on when they don't think anyone is watching? Well, as these pictures show, they're not going after each other tooth and claw.

Nancy Ward, the park's acting chief of maintenance, was heading to Lake for a meeting back on May 4, before the park's interior roads were open for the public, when she spied a wolf and another animal in a snow-covered drainage.

As she continued on, she thought the other animal might be a bison struggling in the snow. With some time to spare, she turned around and headed back to where she had seen the animals. This is what she discovered:

There was a spot cleared right across the river from these two. Once I stopped I was able to look closely and saw the wolf was "playing" with a grizzly bear. I thought they might be attracted to a carcass, but there was no food around. The bear rolled on its back with its feet in the air. It also slid around the snow. The wolf stayed close, checking things out. The bear approached the wolf and they appeared to sniff around each other and on the ground. I had my camera so I took several pictures. They interacted for more than five minutes and then they both walked up the small drainage and out of sight. I don't know if that's a common type of encounter, but I doubt I will ever see it again!