If I had to pick one photo that I've taken where everything hinged on the moment, this would be the one.

This sequence is from a wolf pursuit of a female elk in the Lamar Valley of Yellowstone National Park, May 18, 2013. Although both the elk and wolf were injured in the encounter, both escaped with their lives. The wolf is one of four female 2-year old members of the Lamar Canyon pack. Read much more about this hour-long battle here.

Later in the day, we met up with one of the wolf biologists with National Park Service, and showed him the photos. He was very surprised that this wolf, one that he knew immediately, would attack without the protection of a pack. Elks are extremely strong and the wolf risked it all in its pursuit of prey.

Canon EOS 5D, Canon 100-400mm f/4.5/5.6L IS @ 400mm with Canon 1.4X Teleconverter III - effective focal length - 560mm, 1/2000 sec @f/8, ISO equiv 640, Calumet 8000 Carbon Fiber Tripod, Gitzo G1276 Ballhead