• [Wiki] http://en.wikipedia.org/wiki/Empidonax_difficilis.
• [AnAge] http://genomics.senescence.info/species/entry.php?species=Empidonax_difficilis.
• [avibase] https://avibase.bsc-eoc.org/species.jsp?lang=EN&avibaseid=44A2028364A252A6&sec=lifehistory.
• [DaviFisl1963] Davis, J., Fisler, G. F., and Davis, B. S. (1963). The breeding biology of the western flycatcher. The Condor, 65(5):337--382.
• [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.