Editing Bird migration (section)

==Physiology and control==
The control of migration, its timing and response are genetically controlled and appear to be a primitive trait that is present even in non-migratory species of birds. The ability to navigate and orient themselves during migration is a much more complex phenomenon that may include both endogenous programs as well as learning.<ref>{{cite journal |vauthors=Helm B, Gwinner E |year=2006 |title=Migratory Restlessness in an Equatorial Nonmigratory Bird |journal=PLOS Biol. |volume=4 |issue=4 |page=e110 |doi=10.1371/journal.pbio.0040110 |pmid=16555925 |pmc=1420642 |doi-access=free }}</ref><ref>{{Cite journal |last1=Frias-Soler |first1=Roberto Carlos |last2=Pildaín |first2=Lilian Villarín |last3=Pârâu |first3=Liviu G. |last4=Wink |first4=Michael |last5=Bairlein |first5=Franz |title=Transcriptome signatures in the brain of a migratory songbird |journal=Comparative Biochemistry and Physiology Part D: Genomics and Proteomics |year=2020 |language=en |volume=34 |pages=100681 |doi=10.1016/j.cbd.2020.100681 |pmid=32222683|s2cid=214716503 }}</ref>

===Timing===
The primary physiological cue for migration is the changes in the day length. These changes are related to hormonal changes in the birds. In the period before migration, many birds display higher activity or [[Zugunruhe]] ({{langx |de|migratory restlessness}}), first described by [[Johann Friedrich Naumann]] in 1795, as well as physiological changes such as increased fat deposition. The occurrence of Zugunruhe even in cage-raised birds with no environmental cues (e.g. shortening of day and falling temperature) has pointed to the role of circannual [[endogenous]] programs in controlling bird migrations.<ref>{{cite journal |title=Stopover decision during migration: physiological conditions predict nocturnal restlessness in wild passerines |last=Fusani |first=L. |author2=Cardinale, L. |author3=Carere, C. |author4=Goymann, W. |journal=Biology Letters |year=2009 |doi=10.1098/rsbl.2008.0755 |pmid=19324648 |pmc=2679912 |volume=5 |issue=3 |pages=302–305}}</ref> Caged birds display a preferential flight direction that corresponds with the migratory direction they would take in nature, changing their preferential direction at roughly the same time their wild conspecifics change course.<ref>{{cite journal |url=http://jeb.biologists.org/content/202/16/2225.full.pdf |author1=Nievergelt, F. |author2=Liechti, F. |author3=Bruderer, B. |title=Migratory directions of free-flying birds versus orientation in registration cages |journal=Journal of Experimental Biology |year=1999 |volume=202 |pages=2225–2231 |issue=16 |doi=10.1242/jeb.202.16.2225 |pmid=10409493|bibcode=1999JExpB.202.2225N }}</ref>

[[Satellite]] tracking of 48 individual Asian houbaras (''[[MacQueen's bustard|Chlamydotis macqueenii]]'') across multiple migrations showed that this species uses the local temperature to time their spring migration departure. Notably, departure responses to temperature varied between individuals but were individually repeatable (when tracked over multiple years). This suggests that individual use of temperature is a cue that allows for population-level [[climate change adaptation|adaptation to climate change]]. In other words, in a warming world, many migratory birds are predicted to depart earlier in the year for their summer or winter destination.<ref>{{Cite journal|last1=Burnside|first1=Robert J.|last2=Salliss|first2=Daniel|last3=Collar|first3=Nigel J.|last4=Dolman|first4=Paul M.|date=2021-07-13|title=Birds use individually consistent temperature cues to time their migration departure|journal=Proceedings of the National Academy of Sciences|language=en|volume=118|issue=28|pages=e2026378118|doi=10.1073/pnas.2026378118|issn=0027-8424|pmid=34260383|pmc=8285904|bibcode=2021PNAS..11826378B|doi-access=free}}</ref>

In [[polygyny in animals|polygynous]] species with considerable [[sexual dimorphism]], males tend to return earlier to the breeding sites than their females. This is termed protandry.<ref>{{cite journal |author1=Diego Rubolini |author2=Fernando Spina |author3=Nicola Saino |year=2004 |title=Protandry and sexual dimorphism in trans-Saharan migratory birds |journal=Behavioral Ecology |volume=15 |issue=4 |pages=592–601 |doi=10.1093/beheco/arh048 |citeseerx=10.1.1.498.7541}}</ref><ref>{{cite journal |author1=Edwards, Darryl B. |author2=Forbes, Mark R. |year=2007 |title=Absence of protandry in the spring migration of a population of Song Sparrows Melospiza melodia |journal=Ibis |volume=149 |issue=4 |pages=715–720 |doi=10.1111/j.1474-919X.2007.00692.x}}</ref>

===Orientation and navigation===
[[File:Bar-tailed Godwit migration.jpg |thumb |300px |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|nmi|round=50|abbr=on}}.]]
{{Main |Animal navigation}}
[[Animal navigation|Navigation]] is based on a variety of senses. Many birds have been shown to use a sun compass. Using the Sun for direction involves the need for making compensation based on the time. Navigation has been shown to be based on a combination of other abilities including the ability to detect magnetic fields ([[magnetoreception]]), use visual landmarks as well as [[olfactory navigation|olfactory cues]].<ref name=walraffpigeon>{{cite book |last=Walraff |first=H. G. |year=2005 |title=Avian Navigation: Pigeon Homing as a Paradigm |publisher=Springer}}</ref>

Long-distance migrants are believed to disperse as young birds and form attachments to potential breeding sites and to favourite wintering sites. Once the site attachment is made they show high site-fidelity, visiting the same wintering sites year after year.<ref>{{cite book |last1=Ketterson |first1=E. D. |last2=Nolan | first2=V. Jr. |year=1990 |chapter=Site attachment and site fidelity in migratory birds: experimental evidence from the field and analogies from neurobiology |title=Bird Migration |editor=E. Gwinner |publisher=Springer |pages=117–129 |chapter-url=http://www.indiana.edu/~kettlab/ellen/pubs/KettersonNolan1990.pdf |archive-url=https://web.archive.org/web/20090614142136/http://www.indiana.edu/%7Ekettlab/ellen/pubs/KettersonNolan1990.pdf |archive-date=2009-06-14 |url-status=dead}}</ref>

The ability of birds to navigate during migrations cannot be fully explained by endogenous programming, even with the help of responses to environmental cues. The ability to successfully perform long-distance migrations can probably only be fully explained with an accounting for the cognitive ability of the birds to recognize habitats and form mental maps. [[Satellite tracking (animal migration)|Satellite tracking]] of day migrating raptors such as ospreys and honey buzzards has shown that older individuals are better at making corrections for wind drift.<ref name = migrating>{{cite journal |author1=Thorup, Kasper |author2=Thomas Alerstam |author3=Mikael Hake |author4=Nils Kjelle |year=2003 |title=Bird orientation: compensation for wind drift in migrating raptors is age dependent |journal=[[Proceedings of the Royal Society B]] |volume=270 |pages=S8–S11 |doi=10.1098/rsbl.2003.0014 |pmid= 12952622 |pmc=1698035 |issue=Suppl 1}}</ref> Birds rely for navigation on a combination of innate biological senses and experience, as with the two [[Electromagnetism|electromagnetic]] tools that they use. A young bird on its first migration flies in the correct direction according to the Earth's [[magnetic field]], but does not know how far the journey will be. It does this through a [[radical pair mechanism]] whereby chemical reactions in special [[biological pigment|photo pigments]] sensitive to short wavelengths are affected by the field. Although this only works during daylight hours, it does not use the position of the Sun in any way. With experience, it learns various landmarks and this "mapping" is done by [[magnetite]]s in the [[trigeminal system]], which tell the bird how strong the field is. Because birds migrate between northern and southern regions, the magnetic field strengths at different [[latitude]]s let it interpret the radical pair mechanism more accurately and let it know when it has reached its destination.<ref>{{cite journal |last=Wiltschko |first=W. |author2=U. Munro |author3=H. Ford |author4=R. Wiltschko |year=2006 |title=Bird navigation: what type of information does the magnetite-based receptor provide? |journal=[[Proceedings of the Royal Society B]] |volume=273 |pages=2815–20 |doi=10.1098/rspb.2006.3651 |pmid=17015316 |issue=1603 |pmc=1664630}}</ref> There is a neural connection between the eye and "Cluster N", the part of the forebrain that is active during migrational orientation, suggesting that birds may actually be able to ''see'' the magnetic field of the Earth.<ref>{{cite journal |last1=Heyers |first1=D. |last2=Manns |first2=M. |others=Luksch. H; Güntürkün, O; Mouritsen, H. |year=2007 |title=A Visual Pathway Links Brain Structures Active during Magnetic Compass Orientation in Migratory Birds |journal=PLOS ONE |volume=2 |issue=9 |page=e937 |doi=10.1371/journal.pone.0000937 |pmid=17895978 |pmc=1976598 |bibcode=2007PLoSO...2..937H |editor1-last=Iwaniuk |editor1-first=Andrew|doi-access=free }}</ref><ref>{{cite journal |last=Deutschlander |first=M. E. |author2=Phillips, J. B. |author3=Borland, SC |year=1999 |title=The case for light-dependent magnetic orientation in animals |journal=Journal of Experimental Biology |volume=202 |pages=891–908 |url=http://jeb.biologists.org/cgi/reprint/202/8/891 |issue=8 |doi=10.1242/jeb.202.8.891 |pmid=10085262|bibcode=1999JExpB.202..891D |url-access=subscription }}</ref>

===Vagrancy===
{{See also |Vagrancy (biology)#In birds}}

Migrating birds can lose their way and appear outside their normal ranges. This can be due to flying past their destinations as in the "spring overshoot"{{anchor |overshoot}} in which birds returning to their breeding areas overshoot and end up further north than intended. Certain areas, because of their location, have become famous as watchpoints for such birds. Examples are the [[Point Pelee National Park]] in Canada, and [[Spurn]] in [[England]].

[[Reverse migration (bird migration)|Reverse migration]], where the genetic programming of young birds fails to work properly, can lead to rarities turning up as vagrants thousands of kilometres out of range.<ref>{{cite journal |url=http://www.zmuc.dk/VerWeb/staff/kthorup/Kt-pdf/BirdStudy51-228.pdf |title=Reverse migration as a cause of vagrancy |author=Thorup, Kasper |journal=Bird Study |year=2004 |volume=51 |issue=3 |pages=228–238 |doi=10.1080/00063650409461358 |bibcode=2004BirdS..51..228T |s2cid=51681037 |access-date=2014-06-15 |archive-url=https://web.archive.org/web/20170525094621/http://www.zmuc.dk/VerWeb/staff/kthorup/Kt-pdf/BirdStudy51-228.pdf |archive-date=2017-05-25 |url-status=dead}}</ref>

[[Drift migration]] of birds blown off course by the wind can result in "falls" of large numbers of migrants at coastal sites.<ref name="migrating" />

A related phenomenon called "abmigration" involves birds from one region joining similar birds from a different breeding region in the common winter grounds and then migrating back along with the new population. This is especially common in some waterfowl, which shift from one flyway to another.<ref>{{cite journal |last1=Guillemain |first1=M. |last2=Sadoul |first2=N. |last3=Simon |first3=G. |year=2005 |title=European flyway permeability and abmigration in Teal Anas crecca, an analysis based on ringing recoveries |journal=Ibis |volume=147 |issue=4 |pages=688–696 |doi=10.1111/j.1474-919X.2005.00446.x}}</ref>

===Migration conditioning===

It has been possible to teach a migration route to a flock of birds, for example in re-introduction schemes. After a trial with [[Canada goose|Canada geese]] ''Branta canadensis'', [[microlight]] aircraft were used in the US to teach safe migration routes to reintroduced [[whooping crane]]s ''Grus americana''.<ref>{{cite web |url=http://www.operationmigration.org/index.html |title=Operation migration|date=7 September 2021 }}</ref><ref>{{cite web |url=http://dnr.wi.gov/files/pdf/pubs/er/er0650.pdf |title=Wisconsin Whooping Crane Management Plan |publisher=Wisconsin Department of Natural Resources |date=6 December 2006}}</ref>