What is birkie fever? Cross-country skiers are hearty folk. The compulsion to race marathon-length distances in subfreezing conditions requires an eternally optimistic and fiercely independent spirit. The fear of blinding snow or paralyzing cold does not deter them, and it has been said that skiers do not merely laugh at adversity; they are completely oblivious to its existence. America's greatest cross-country ski race is the American Birkebeiner or "Birkie" for short.