The Astonishing Sight of 25 Wolves Tracking Bison: Witnessing the Magnitude of an Extraordinary Wolf Pack.

This video is the first of its kind. A pack of northern gray wolves — at 25 members strong, one of the largest wolf packs ever filmed — chases down a herd of wood bison, the largest land animals in North America.

This scene from the upcoming Frozen Planet series was filmed in Wood Buffalo National Park in Canada’s Northwest Territories at the height of the Arctic winter. At -40°F, this was the coldest shoot of the entire series.

The filmmakers used an aerial camera, mounted to the side of a helicopter, that was controlled from inside via a computer and joystick. Forgoing warmth in favor of dexterity, aerial cameraman Michael Calin — a native of southern sunny California, who had never experienced temperatures like these before — made the tough decision to remove his heavy gloves in order to keep up with the action.

The camera itself was wrapped in insulation; at -40°F, electrical cables can easily short-circuit. Calin and Director Chadden Hunter flew for hundreds of miles before spotting the wolf pack, which was already on the hunt. From the helicopter, they could shadow the wolves without influencing their natural behavior.

Once the chase started, Calin and the helicopter pilot had to work as one in order to keep the shot smooth. They were unprepared for what happened.