A. Wetmore, A. Thomson. Additional specimens of fossil birds from the upper tertiary deposits of Nebraska. In: American Museum Novitates 1928, 302, Weblink (PDF; 404 kB)
fws.gov
U.S. Fish & Wildlife Service, S. Delany, S. Scott, D.C. Bryan. Waterbird Status Assessment 2002, Weblink (PDF; 226 kB)