 Investigation in Yellowstone National Park showed that elk , followed by mule deer , were the cougar 's primary targets ; the prey base is shared with the park 's gray wolves , with which the cougar competes for resources . Another study on winter kills ( November – April ) in Alberta showed that ungulates accounted for greater than 99 % of the cougar diet . Learned , individual prey recognition was observed , as some cougars rarely killed <unk> sheep , while others relied heavily on the species . 
