Strangely enough, these are coyotes working together to hunt elk. You can see these two facing the elk head on, what you can't see are the other two coming around from the right side of the photo over the hill.
For those of you who don't know, coyotes are not pack animals, in fact it's rare to see two or more together (other than a mother with pups or a couple juveniles), but never have I heard of coyotes working as a pack of 4. They eventually chased the elk over the hill and we couldn't see what played out from there, but it was an exciting experience.

January 2012
Lamar Valley, Yellowstone National Park

Also my January photo contest submission to the  photografurs