Anas poecilorhyncha, zonorhyncha and other ducks
Allan C. Brooks
<cite class="book" style="font-style:normal">Phillips, John C. (1923)      <i> <a rel="nofollow" class="external text" href="https://archive.org/stream/naturalhistoryof02phil#page/n137/mode/2up">A natural history of the ducks. Volume II</a></i>, Houghton Mifflin, pp. 90−96  <small></small></cite>