Söderholm, S. (2006). Does the Pochard Aythya ferina vary periodically?—an analysis of census data from Angarnsjöängen, Sweden 1978—2003 and Lake Engure, Latvia 1972—1992. Ornis Svecica, 16(3), 85–94. https://doi.org/10.34080/os.v16.22712