Editing Bird (section)

===Migration===
{{Main|Bird migration}}
[[File:CanadianGeeseFlyingInVFormation.jpg|thumb|A flock of [[Canada geese]] in [[V formation]]]]
Many bird species migrate to take advantage of global differences of [[season]]al temperatures, therefore optimising availability of food sources and breeding habitat. These migrations vary among the different groups. Many landbirds, [[shorebird]]s, and [[waterbird]]s undertake annual long-distance migrations, usually triggered by the length of daylight as well as weather conditions. These birds are characterised by a breeding season spent in the [[temperate]] or [[polar region]]s and a non-breeding season in the [[tropical]] regions or opposite hemisphere. Before migration, birds substantially increase body fats and reserves and reduce the size of some of their organs.<ref name="Battley">{{Cite journal|last1=Battley |first1=Phil F. |date=January 2000 |title=Empirical evidence for differential organ reductions during trans-oceanic bird flight |journal=[[Proceedings of the Royal Society B]] |volume=267 |issue=1439 |pages=191–195 |doi=10.1098/rspb.2000.0986 |pmid=10687826 |last2=Piersma |first2=T. |last3=Dietz |first3=M. W.|last4=Tang |first4=S |last5=Dekinga |first5=A. |last6=Hulsman |first6=K. |pmc=1690512}} (Erratum in ''Proceedings of the Royal Society B'' '''267'''(1461):2567.)</ref><ref name="Klaassen">{{Cite journal|last=Klaassen |first=Marc |date=1 January 1996|title=Metabolic constraints on long-distance migration in birds |journal=Journal of Experimental Biology |volume=199 |issue=1 |pages=57–64 |doi=10.1242/jeb.199.1.57 |pmid=9317335 |bibcode=1996JExpB.199...57K |url=http://jeb.biologists.org/cgi/reprint/199/1/57 }}</ref>

Migration is highly demanding energetically, particularly as birds need to cross deserts and oceans without refuelling. Landbirds have a flight range of around {{convert|2500|km|mi|-2|abbr=on}} and shorebirds can fly up to {{convert|4000|km|mi|-2|abbr=on}},<ref name="Gill"/> although the [[bar-tailed godwit]] is capable of non-stop flights of up to {{convert|10200|km|mi|-2|abbr=on}}.<ref>{{Cite news |title=Long-distance Godwit sets new record |url=http://www.birdlife.org/news/news/2007/04/bar-tailed_godwit_journey.html |date=4 May 2007 |publisher=[[BirdLife International]] |access-date=13 December 2007 |archive-date=2 October 2013 |archive-url=https://web.archive.org/web/20131002131732/http://www.birdlife.org/news/news/2007/04/bar-tailed_godwit_journey.html }}</ref> Some [[seabird]]s undertake long migrations, with the longest annual migrations including those of [[Arctic terns]], which were recorded travelling an average of {{convert|70900|km|abbr=on}} between their [[Arctic]] breeding grounds in [[Greenland]] and [[Iceland]] and their wintering grounds in [[Antarctica]], with one bird covering {{convert|81600|km|abbr=on}},<ref>{{cite journal |last1=Egevang |first1=Carsten |last2=Stenhouse |first2=Iain J. |last3=Phillips |first3=Richard A. |last4=Petersen |first4=Aevar |last5=Fox |first5=James W. |last6=Silk |first6=Janet R. D. |year=2010 |title=Tracking of Arctic terns ''Sterna paradisaea'' reveals longest animal migration |journal=Proceedings of the National Academy of Sciences |volume=107 |issue=5 |pages=2078–2081 |doi=10.1073/pnas.0909493107 |doi-access=free |pmid=20080662 |pmc=2836663 |bibcode=2010PNAS..107.2078E }}</ref> and [[sooty shearwater]]s, which nest in [[New Zealand]] and [[Chile]] and make annual round trips of {{convert|64000|km|mi|-2|abbr=on}} to their summer feeding grounds in the North Pacific off Japan, [[Alaska]] and [[California]].<ref>{{Cite journal|last1=Shaffer |first1=Scott A. |year=2006 |title=Migratory shearwaters integrate oceanic resources across the Pacific Ocean in an endless summer |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=103 |issue=34 |pages=12799–12802 |doi=10.1073/pnas.0603715103 |pmid= 16908846 |last2=Tremblay |first2=Y.. |last3=Weimerskirch |first3=H. |last4=Scott |first4=D |last5=Thompson |first5=DR |last6=Sagar |first6=PM |last7=Moller |first7=H. |last8=Taylor |first8=G. A. |last9=Foley |first9=D. G.|pmc=1568927|first10=B. A.|last10=Block|first11=D. P.|last11=Costa|display-authors=1 |bibcode=2006PNAS..10312799S |doi-access=free }}</ref>
Other seabirds disperse after breeding, travelling widely but having no set migration route. [[Albatross]]es nesting in the [[Southern Ocean]] often undertake circumpolar trips between breeding seasons.<ref>{{Cite journal|last1=Croxall |first1=John P. |year=2005 |title=Global Circumnavigations: Tracking year-round ranges of nonbreeding Albatrosses |journal=Science |volume=307 |issue=5707 |pages=249–250 |doi=10.1126/science.1106042 |pmid=15653503 |last2=Silk |first2=J. R. |last3=Phillips |first3=R. A. |last4=Afanasyev |first4=V. |last5=Briggs |first5=D. R.|bibcode=2005Sci...307..249C }}</ref>

[[File:Bar-tailed Godwit migration.jpg|alt= A map of the Pacific Ocean with several coloured lines representing bird routes running from New Zealand to Korea|thumb|left|The routes of satellite-tagged [[bar-tailed godwit]]s migrating north from [[New Zealand]]. This species has the longest known non-stop migration of any species, up to {{convert|10200|km|mi|-2|abbr=on}}.]]
Some bird species undertake shorter migrations, travelling only as far as is required to avoid bad weather or obtain food. [[wikt:irruptive|Irruptive]] species such as the boreal [[finch]]es are one such group and can commonly be found at a location in one year and absent the next. This type of migration is normally associated with food availability.<ref>{{Cite journal|last=Wilson | first=W. Herbert Jr. |year=1999 |title=Bird feeding and irruptions of northern finches:are migrations short stopped? |journal=North America Bird Bander |volume=24 |issue=4 |pages=113–121 |url=http://sora.unm.edu/sites/default/files/journals/nabb/v024n04/p0113-p0121.pdf |archive-url=https://web.archive.org/web/20140729162642/https://sora.unm.edu/sites/default/files/journals/nabb/v024n04/p0113-p0121.pdf |archive-date=29 July 2014 }}</ref> Species may also travel shorter distances over part of their range, with individuals from higher latitudes travelling into the existing range of conspecifics; others undertake partial migrations, where only a fraction of the population, usually females and subdominant males, migrates.<ref>{{Cite journal|last1=Nilsson |first1=Anna L.K. |year=2006 |title=Do partial and regular migrants differ in their responses to weather? |journal=The Auk |volume=123 |issue=2 |pages=537–547 |doi=10.1642/0004-8038(2006)123[537:DPARMD]2.0.CO;2 |last2=Alerstam |first2=Thomas |last3=Nilsson |first3=Jan-Åke |doi-access=free }}</ref> Partial migration can form a large percentage of the migration behaviour of birds in some regions; in Australia, surveys found that 44% of non-passerine birds and 32% of passerines were partially migratory.<ref>{{Cite journal|last=Chan |first=Ken |year=2001 |title=Partial migration in Australian landbirds: a review |journal=[[Emu (journal)|Emu]] |volume=101 |issue=4 |pages=281–292 |doi=10.1071/MU00034|bibcode=2001EmuAO.101..281C }}</ref>

[[Altitudinal migration]] is a form of short-distance migration in which birds spend the breeding season at higher altitudes and move to lower ones during suboptimal conditions. It is most often triggered by temperature changes and usually occurs when [[territory (animal)|the normal territories]] also become inhospitable due to lack of food.<ref>{{Cite journal|last=Rabenold |first=Kerry N. |year=1985 |title=Variation in Altitudinal Migration, Winter Segregation, and Site Tenacity in two subspecies of Dark-eyed Juncos in the southern Appalachians |journal=The Auk |volume=102 |issue=4 |pages=805–819 |url=http://sora.unm.edu/sites/default/files/journals/auk/v102n04/p0805-p0819.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://sora.unm.edu/sites/default/files/journals/auk/v102n04/p0805-p0819.pdf |archive-date=9 October 2022 |url-status=live}}</ref> Some species may also be nomadic, holding no fixed territory and moving according to weather and food availability. [[True parrots|Parrots]] as a [[family (biology)|family]] are overwhelmingly neither migratory nor sedentary but considered to either be dispersive, irruptive, nomadic or undertake small and irregular migrations.<ref>{{Cite book|last=Collar |first=Nigel J. |year=1997 |chapter=Family Psittacidae (Parrots) |title=Handbook of the Birds of the World |series=Vol. 4: Sandgrouse to Cuckoos |editor=Josep del Hoyo |editor2=Andrew Elliott |editor3=Jordi Sargatal |location=Barcelona |publisher=Lynx Edicions |isbn=84-87334-22-9|title-link=Handbook of the Birds of the World }}</ref>

The ability of birds to return to precise locations across vast distances has been known for some time; in an experiment conducted in the 1950s, a [[Manx shearwater]] released in [[Boston]] in the United States returned to its colony in [[Skomer]], in Wales within 13 days, a distance of {{convert|5150|km|mi|-2|abbr=on}}.<ref>{{Cite journal|last=Matthews |first=G.V.T. |date=1 September 1953 |title=Navigation in the Manx Shearwater |journal=Journal of Experimental Biology |volume=30 |issue=2 |pages=370–396 |doi=10.1242/jeb.30.3.370 |doi-access=free|bibcode=1953JExpB..30..370M }}</ref> Birds navigate during migration using a variety of methods. For [[diurnal animal|diurnal]] migrants, the [[sun]] is used to navigate by day, and a stellar compass is used at night. Birds that use the sun compensate for the changing position of the sun during the day by the use of an [[Chronobiology|internal clock]].<ref name="Gill"/> Orientation with the stellar compass depends on the position of the [[constellation]]s surrounding [[Polaris]].<ref>{{Cite journal|last1=Mouritsen |first1=Henrik |last2=Larsen |first2=Ole Næsbye |date=15 November 2001 |title=Migrating songbirds tested in computer-controlled Emlen funnels use stellar cues for a time-independent compass |journal=Journal of Experimental Biology |volume=204 |issue=8 |pages=3855–3865 |pmid=11807103 |doi=10.1242/jeb.204.22.3855 |doi-access=free|bibcode=2001JExpB.204.3855M }}</ref> These are backed up in some species by their ability to sense the Earth's [[geomagnetism]] through specialised [[Photoreceptor cell|photoreceptors]].<ref>{{Cite journal|last1=Deutschlander |first1=Mark E. |last2=Phillips |first2=J. B. |last3=Borland |first3=S. C. |date=15 April 1999 |title=The case for light-dependent magnetic orientation in animals |journal=Journal of Experimental Biology |volume=202 |issue=8 |pages=891–908 |pmid=10085262 |doi=10.1242/jeb.202.8.891 |doi-access=free|bibcode=1999JExpB.202..891D }}</ref>