Thomas, G.B.Jr. (1960) Calculus and analytic geometry. 3rd Edition, Addison-Wesley, Reading, 565-571.
 Peterson, R.T. (1980) A field guide to the birds. 4th Edition, Houghton Mifflin Co., Boston.
 Kortright, F.J. (1967) The ducks, geese and swans of North America. The Stackpole Company, Harrisburg, Wildlilfe Management Institute, Washington, DC.
 Box, G.E.P., Hunter, W.G. and Hunter, J.S. (1978) Statistics for experimenters. John Wiley & Sons Ltd., Chichester, 203-207.
 Bejan, A. (2004) Convection heat transfer, 3RD Edition, Wiley, New York, 63-66.