• [Wiki] http://en.wikipedia.org/wiki/Upupa_epops.
• [AnAge] http://genomics.senescence.info/species/entry.php?species=Upupa_epops.
• [EoL] http://eol.org/pages/917145/overview.
• [HildScha2017] Hildebrandt, B. and Schaub, M. (2017). The effects of hatching asynchrony on growth and mortality patterns in Eurasian hoopoe Upupa epops nestlings. Ibis, 160:145--157. doi:10.1111/ibi.12529.
• [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.