== Noter ==
{{reflist|2|refs=
<ref name="Hørring">R. Hørring. [http://www.archive.org/stream/danmarksfaunaill23dans#page/n3/mode/2up ''Danmarks Fauna. Fugle I. Andefugle og Hønsefugle'']. Gads Forlag/Dansk naturhistorisk Forening 1919. Copyright udløbet.</ref>
<ref name=Ulfstrand>Staffan Ulfstrand, ''Vad nytta gör en halv vinge?'', "Vår fågelvärld" (et svensk tidsskrift om fugle), nr 6, 2006</ref>
<ref name=Warham>
 {{Cite news |last1 = Warham|first1 = John|date = 1977|titel = The Incidence, Function and ecological significance of petrel stomach oils|work = Proceedings of the New Zealand Ecological Society|volume = 24|page = 84–93|url = http://www.newzealandecology.org/nzje/free_issues/ProNZES24_84.pdf|doi = 10.2307/1365556}} </ref>
<ref name=Dumbacher>
 {{Cite news |last1 = Dumbacher|first1 = J.P.|last2 = B.M. Beehler, T.F. Spande ''et al.''|month = oktober|date = 1992|titel = omobatrachotoxin in the genus ''Pitohui'': chemical defense in birds?|work = Science|volume = 258|issue = 5083|page = 799–801|doi = 10.1126/science.1439786|pmid = 1439786}}</ref>
<ref name=Gill>{{Cite book |last1 = Gill |first1 = Frank |year = 1995 |title = Ornithology |url = https://archive.org/details/ornithology0000gill |edition = Anden |place = New York |publisher = W.H. Freeman |isbn = 0-7167-2415-4 |page =}}</ref>
<ref name="Göth">
 {{Cite news |last1 = Göth|first1 = Anne|titel = Incubation temperatures and sex ratios in Australian brush-turkey (''Alectura lathami'') mounds|work = Austral Ecology|date = 2007|volume = 32|issue = 4|page = 278–85|doi = 10.1111/j.1442-9993.2007.01709.x}}
</ref>
<ref name=Ehrlich> Ehrlich, Paul R. (1988). [http://www.stanford.edu/group/stanfordbirds/text/essays/Adaptations.html ''Adaptations for Flight'']. Birds of Stanford. Stanford University. Læst 2013-05-23. Baseret på ''The Birder's Handbook'' (Paul Ehrlich, David Dobkin og Darryl Wheye. 1988. Simon and Schuster, New York.)
</ref>
<ref name=paulnoll>
 {{Cite news | titel = The Avian Skeleton| url = http://www.paulnoll.com/Oregon/Birds/Avian-Skeleton.html| work = paulnoll.com}} Læst 2013-05-23.
</ref>
<ref name=Halskotor>[http://www.nrm.se/sv/meny/faktaomnaturen/djur/faglar/skelettfranfaglar/faglarsskelett/halskotor.376.html Halskotor - Naturhistoriska riksmuseet] {{Webarchive|url=https://web.archive.org/web/20081121153218/http://www.nrm.se/sv/meny/faktaomnaturen/djur/faglar/skelettfranfaglar/faglarsskelett/halskotor.376.html |date=21. november 2008 }}. Læst 23. maj 2013.</ref>
<ref name=Fernbank>
 {{Cite news | titel = Skeleton of a typical bird| url = http://fsc.fernbank.edu/Birding/skeleton.htm| work = Fernbank Science Center's Ornithology Web}} Læst 2013-05-23.</ref>
<ref name=EhrlichD>Ehrlich, Paul R. (1988). [http://www.stanford.edu/group/stanfordbirds/text/essays/Drinking.html Drinking]. ''Birds of Stanford''. Stanford University. Læst 2013-05-23</ref>
<ref name=Tsahar>
 {{Cite news |last1 = Tsahar|first1 = Ella|last2 = Carlos Martínez del Rio, Ido Izhaki och Zeev Arad|titel = Can birds be ammonotelic? Nitrogen balance and excretion in two frugivores|work = Journal of Experimental Biology|volume = 208|issue = 6|page = 1025–34|date = 2005|pmid = 15767304|doi = 10.1242/jeb.01495}}</ref>
<ref name=Preest>
 {{Cite news |last1 = Preest|first1 = Marion R.|last2 = Carol A. Beuchat|month = april|date = 1997|titel = Ammonia excretion by hummingbirds|work = Nature|volume = 386|page = 561–62|doi = 10.1038/386561a0}}</ref>
<ref name=Mora>
 {{Cite news |last1 = Mora|first1 = J.|last2 = J. Martuscelli, Juana Ortiz-Pineda och G. Soberón|date = 1965|titel = The Regulation of Urea-Biosynthesis Enzymes in Vertebrates|work = Biochemical Journal|volume = 96|page = 28–35|pmid = 14343146|url = http://www.biochemj.org/bj/096/0028/0960028.pdf}}</ref>
<ref name=Packard>
 {{Cite news |last1 = Packard|first1 = Gary C.|date = 1966|titel = The Influence of Ambient Temperature and Aridity on Modes of Reproduction and Excretion of Amniote Vertebrates|work = The American Naturalist|volume = 100|issue = 916|page = 667–82|url = http://www.jstor.org/discover/10.2307/2459303?uid=3737880&uid=2&uid=4&sid=21102322247667|doi = 10.1086/282459}}</ref>
<ref name=Balgooyen>{{Cite news|last1 = Balgooyen|first1 = Thomas G.|date = 1971|titel = Pellet Regurgitation by Captive Sparrow Hawks (''Falco sparverius'')|work = [[Condor]]|volume = 73|issue = 3|page = 382–85|doi = 10.2307/1365774|url = http://elibrary.unm.edu/sora/Condor/files/issues/v073n03/p0382-p0385.pdf|access-date = 24. maj 2013|archive-url = https://web.archive.org/web/20090325023305/http://elibrary.unm.edu/sora/Condor/files/issues/v073n03/p0382-p0385.pdf}}</ref>
<ref name=Gionfriddo>{{Cite news|last1 = Gionfriddo|first1 = James P.|last2 = Louis B. Best|month = februari|date = 1995|titel = Grit Use by House Sparrows: Effects of Diet and Grit Size|work = Condor|volume = 97|issue = 1|page = 57–67|doi = 10.2307/1368983|url = http://elibrary.unm.edu/sora/Condor/files/issues/v097n01/p0057-p0067.pdf|access-date = 24. maj 2013|archive-url = https://web.archive.org/web/20090325023232/http://elibrary.unm.edu/sora/Condor/files/issues/v097n01/p0057-p0067.pdf}}</ref>
<ref name=Attenborough>
 {{Cite book |last1 = Attenborough |first1 = David |author-link1 = David Attenborough |year = 1998 |title = The Life of Birds |url = https://archive.org/details/lifeofbirds00unse |place = Princeton |publisher = Princeton University Press |isbn = 0-691-01633-X}}</ref> 
<ref name=Cockburn2>{{Cite news |last1 = Cockburn|first1 = Andrew|date = 2006|titel = Prevalence of different modes of parental care in birds|doi = 10.1098/rspb.2005.3458 |work = Proceedings: Biological Sciences|volume = 273|issue = 1592|page = 1375–83|pmid = 16777726}}
</ref>
<ref name=Battley>
 {{Cite news |last1 = Battley|first1 = Phil F.|last2 = Theunis Piersma, Maurine W. Dietz ''et al.''|month = januari|date = 2000|titel = Empirical evidence for differential organ reductions during trans-oceanic bird flight|work = Proceedings of the Royal Society B|volume = 267|issue = 1439|page = 191–5|doi = 10.1098/rspb.2000.0986|pmid = 10687826}}  (Erratum i ''Proceedings of the Royal Society B'' '''267'''(1461):2567.)</ref>
<ref name=Maina>
 {{Cite news |last1 = Maina|first1 = John N.|month = November|date = 2006|titel = Development, structure, and function of a novel respiratory organ, the lung-air sac system of birds: to go where no other vertebrate has gone|work = Biological Reviews|volume = 81|issue = 4|page = 545–79|doi = 10.1111/j.1469-185X.2006.tb00218.x|pmid = 17038201|doi-broken-date = 2008-06-28}}</ref>
<ref name=Suthers>
 {{Cite book |last1 = Suthers |first1 = Roderick A. |last2 = Sue Anne Zollinger |chapter = Producing song: the vocal apparatus |editor = H. Philip Zeigler & Peter Marler (red.) |year = 2004 |title = Behavioral Neurobiology of Birdsong |series = Annals of the New York Academy of Sciences '''1016''' |place = New York |publisher = New York Academy of Sciences |isbn = 1-57331-473-0 |page = 109-129 |doi = 10.1196/annals.1298.041}}  {{PMID|15313772}}</ref>
<ref name=Scott>
 {{Cite news |last1 = Scott|first1 = Robert B.|month = mars|date = 1966|titel = Comparative hematology: The phylogeny of the erythrocyte|work = Annals of Hematology|volume = 12|issue = 6|page = 340–51|doi = 10.1007/BF01632827|pmid = 5325853}}</ref>
<ref name=Roots>
 {{Cite book |last1 = Roots |first1 = Clive |year = 2006 |title = Flightless Birds |place = Westport |publisher = Greenwood Press |isbn = 978-0-313-33545-7}}</ref> 
<ref name=McNab>
 {{Cite news |last1 = McNab|first1 = Brian K.|month = oktober|date = 1994|titel = Energy Conservation and the Evolution of Flightlessness in Birds|work = The American Naturalist|volume = 144|issue = 4|page = 628–42|url = http://links.jstor.org/sici?sici=0003-0147(199410)144:4%3C628:ECATEO%3E2.0.CO;2-D|doi = 10.1086/285697}}</ref> 
<ref name=Kovacs>
 {{Cite news |last1 = Kovacs|first1 = Christopher E.|last2 = Ron A. Meyers|month = maj|date = 2000|titel = Anatomy and histochemistry of flight muscles in a wing-propelled diving bird, the Atlantic Puffin, ''Fratercula arctica''|work = Journal of Morphology|volume = 244|issue = 2|page = 109–25|doi = 10.1002/(SICI)1097-4687(200005)244:2<109::AID-JMOR2>3.0.CO;2-0 }}</ref>
<ref name="östling">{{Cite book
|last1=Östling
|first1=Brutus
|last2=Åkesson Susanne
|title=Att överleva dagen: om fåglars sinnen och anpassningsförmåga
|year=2009
|publisher=Brutus Östlings bokförlag Symposion
|place=Eslöv
|language=svensk
|isbn=978-91-7139-840-6
|url=http://www.symposion.se/books/nya_09/overleva.pdf
}}</ref>
<ref name="Adriansen1">[[Inge Adriansen]], ''Nationale symboler i det Danske Rige, 1830-2000'', bind 2, side 400. [[Museum Tusculanums Forlag]] 2003 [http://books.google.dk/books?id=gJBJtx18H5gC&lpg=PA400&ots=NtXmwesoO4&dq=island%20nationalfugl&hl=da&pg=PA400#v=onepage&q=island%20nationalfugl&f=false Google Books]</ref>
<ref name="snl.no">[http://snl.no/nasjonalfugl Nasjonalfugl] i det ''Store norske leksikon'' på www.snl.no</ref>
<ref name="birdlife.fi">Finlands nationalfugl i [http://www.birdlife.fi/english/finland-for-birdwatchers.shtml Finland for birdwatchers] på www.birdlife.fi</ref>
<ref name="Adriansen">[[Inge Adriansen]], ''Nationale symboler i det Danske Rige, 1830-2000'', bind 2, side 404. [[Museum Tusculanums Forlag]] 2003 [http://books.google.dk/books?id=gJBJtx18H5gC&lpg=PA404&ots=NtXmwesoO4&dq=island%20nationalfugl&hl=da&pg=PA404#v=onepage&q=island%20nationalfugl&f=false Google Books]</ref>
<ref name="politi.dk">Færøernes nationalfugl [https://www.politi.dk/Faeroeerne/da/omos/Aarsberetning/Politiets+%C3%A5rsberetning+2007.htm?WBCMODE=PresentationUnpublished%2CPresentationU Årsberetning fra Færøernes politi 2007]{{Dødt link|date=januar 2022 |bot=InternetArchiveBot |fix-attempted=yes }} på www.politi.dk</ref>
<ref name=Sales>
 {{Cite news |last1 = Sales|first1 = James|date = 2005|titel = The endangered kiwi: a review|work = Folia Zoologica|volume = 54|issue = 1–2|page = 1–20|url = http://www.ivb.cz/folia/54/1-2/01-20.pdf}}
</ref> 
<ref name="Avian Sense of Smell"> Ehrlich, Paul R. (1988). [http://www.stanford.edu/group/stanfordbirds/text/essays/Avian_Sense.html ''The Avian Sense of Smell'']. Birds of Stanford. Stanford University. Læst 2013-09-15
</ref>
<ref name=Lequette>{{Cite news|last1 = Lequette|first1 = Benoit|last2 = Christophe Verheyden, Pierre Jouventin|month = augusti|date = 1989|titel = Olfaction in Subantarctic seabirds: Its phylogenetic and ecological significance|work = The Condor|volume = 91|issue = 3|page = 732–35|doi = 10.2307/1368131|url = http://elibrary.unm.edu/sora/Condor/files/issues/v091n03/p0732-p0735.pdf|access-date = 16. september 2013|archive-url = https://web.archive.org/web/20120205180101/http://elibrary.unm.edu/sora/Condor/files/issues/v091n03/p0732-p0735.pdf}}</ref>
<ref name=Saito>{{Cite news |last1 = Saito|first1 = Nozomu|date = 1978|titel = Physiology and anatomy of avian ear|work = The Journal of the Acoustical Society of America|volume = 64|issue = S1|page = S3|doi = 10.1121/1.2004193}}
</ref>
<ref name=Rattenborg> Rattenborg, Niels C (2006): ''Evolution of slow-wave sleep and palliopallial connectivity in mammals and birds: a hypothesis''; Brain Research Bulletin 69(1):20-29
</ref>
<ref name=Kavanau>Kavanau (2002): ''REM and NREM sleep as natural accompaniments of the evolution of warm-bloodedness'', Neuroscience and Biobehavioral Reviews 26(8):889-906
</ref>
<ref name=Rattenborg2>Rattenborg, Amlaner, Lima (2000): ''Behavioral, neurophysiological and evolutionary perspectives on unihemispheric sleep'', Neuroscience and Biobehavioral Reviews 24(8):817-42
</ref>
<ref name=Rattenborg3>{{Cite news |last1 = Rattenborg|first1 = Niels C.|date = 2006|titel = Do birds sleep in flight?|work = Die Naturwissenschaften|volume = 93|issue = 9|page = 413–25|doi = 10.1007/s00114-006-0120-3}}
</ref>
Geologi