?Plectropterus gambensis IUCN?, BirdLife International , 2010.

P.  Johnsguard, Handbook of Waterfowl Behavior. Lincoln : University of Nebraska, 1965.

M. A.  Ciaranca, Allin, C. C., and Jones, G. S., Mute Swan (Cygnus olor). In The Birds of North America No 273 , No. 273 (A.Poole and F. Gill) . Philadelphia, PA: The Birds of North America, Inc., 1997.

C. R.  Darwin, The descent of man, and selection in relation to sex. 1871.

M.  Mallory and Metz, K., Common Merganser (Mergus merganser) in The Birds of North America, No. 442. Philadelphia, PA : The Birds of North America, Inc. , 1999.

C. R.  Darwin, ?The descent of man, and selection in relation to sex.?, 1871.

, ?Paradise Duck/ putakitaki/ putangitangi ?, Canterbury Conservancy , Christchurch, 2006.

C. R.  Darwin, The descent of man, and selection in relation to sex., vol. Volume 2 . London: John Murray, 1871.