Bidwell Engebretson Tusen Takk Volunteer Support Fund The American Birkebeiner is America's largest cross-country ski marathon, with a course spanning from Cable to Hayward. It attracts over 10,000 skiers and part of the Worldloppet Circuit and American Ski Marathon series. This Fund supports the volunteer programs of the American Birkebeiner Ski Foundation. Since this is an Agency Endowment Fund, donations must be made through the Endowment for the American Birkebeiner website.