Even in thick snow, bison can run at up to 35mph.
The lead female wolf leads the chase.
A kick from a bison's hind leg could shatter herjaws.
But the pack must feed, and they take turns to attack.
The bison head for cover.
The deep snow slows down both attacked... and attacker.
The herd splits into two. But the wolves are far from giving up.
Hours pass. The thicker vegetation has turned a straightfonnard chase... into a deadly form of hide and seek.
Discovered. The lead female manages to chase the smaller group into the open.
But here the bison are able to close ranks once again.
The leading wolves wait for the rest of the pack to catch up.
The super-pack is once again at full strength.
Suddenly, two of the bison panic. It's just what the wolves have been waiting for.
One of the bison is tiring.
The lead female gets a grip on its flanks. The male joins her.
Together, they might be able to bring it down. The rest of the wolves catch up and help.
After eight long, hard hours, the hunt is coming to an end.
Victory is sounded to summon the rest of the pack.
A single wolf wouldn't stand a chance of making such a kill by itself.
The only way they have of surviving the winter is as a super-pack.