• [Wiki] http://en.wikipedia.org/wiki/Surnia_ulula.
• [avibase] https://avibase.bsc-eoc.org/species.jsp?lang=EN&avibaseid=89F8B6F5598E0C65&sec=lifehistory.
• [DuncDunc2020] Duncan, J. R. and Duncan, P. A. (2020). Northern hawk owl (Surnia ulula), version 1.0. in birds of the world (s. m. billerman, editor). cornell lab of ornithology, ithaca, ny, usa. doi:10.2173/bow.nohowl.01.
• [Kooy2010] Kooijman, S. (2010). Dynamic Energy Budget theory for metabolic organisation. Cambridge Univ. Press, Cambridge.
• [PrinPres1991] Prinzinger, R., A.Preßmar, and Schleucher, E. (1991). Body temperature in birds. Comp. Biochem. Physiol., 99A(4):499--506. doi:10.1016/0300-9629(91)90122-S.