Ruokonen M. & Aarvak T. 2011. Typology revisited: historical taxa of the bean goose — pink-footed goose complex. Ardea 99: 103–112.

Taxonomic practices change over time and this affects the number of taxonomical units recognized. In late 19th and early 20th centuries the number of species increased as a consequence of typological thinking, i.e. classifying all aberrant individuals to a separate species. During this period, several species or subspecies of the bean goose complex were described, and currently their status is either considered not valid or is not agreed upon. We studied individuals from five of the historical taxa, Anser neglectus, A. mentalis, A. oatesi, A. fabalis johanseni and A. fabalis curtus, by using mitochondrial DNA and morphological measurements to clarify their taxonomical status. Overall, we did not find support for additional taxa other than those currently recognized.