North American Waterbird Conservation Plan. 2006. “Conservation Status and Distribution of Solitary-Nesting Waterbird Species [A Species-level Categorization Relative to All Waterbirds and Derived within the Spatial Context of the NAWCP Area].  http://www.waterbirdconservation.org [site discontinued] Accessed June 15, 2016. Printed and scanned version available at https://mnbirdatlas.org/wp-content/uploads/2017/09/Conservation-Status-and-Distribution-of-Solitary-Nesting-Waterbird-Species-2006.pdf