Editing Bird migration (section)

==Evolutionary and ecological factors==

Migration in birds is highly labile and is believed to have developed independently in many avian lineages.<ref>{{cite journal |last=Pulido |first=F. |year=2007 |title=The genetics and evolution of avian migration |journal=BioScience |volume=57 |issue=2 |pages=165–174 |doi=10.1641/b570211 |doi-access=free|hdl=20.500.11755/8f0493ad-d3ff-48bf-b4ae-48c00e8a238a |hdl-access=free }}</ref> While it is agreed that the behavioural and physiological adaptations necessary for migration are under genetic control, some authors have argued that no genetic change is necessary for migratory behaviour to develop in a sedentary species because the genetic framework for migratory behaviour exists in nearly all avian lineages.<ref>{{cite journal |author1=J. Rappole |author2=B. Helm |author3=M. Ramos |year=2003 |title=An integrative framework for understanding the origin and evolution of avian migration |journal=Journal of Avian Biology |volume=34 |issue=1 |page=125 |doi=10.1034/j.1600-048x.2003.03170.x}}</ref> This explains the rapid appearance of migratory behaviour after the most recent glacial maximum.<ref>{{cite journal |author1=B. Mila |author2=T. Smith |author3=R. Wayne. |year=2006 |title=Postglacial population expansion drives the evolution of long-distance avian migration in a songbird |journal=Evolution |volume=60 |issue=11 |pages=2403–2409 |doi=10.1111/j.0014-3820.2006.tb01875.x |pmid=17236431 |s2cid=221736334 |doi-access=free}}</ref>

Theoretical analyses show that detours that increase flight distance by up to 20% will often be adaptive on [[aerodynamics|aerodynamic]] grounds – a bird that loads itself with food to cross a long barrier flies less efficiently. However some species show circuitous migratory routes that reflect historical range expansions and are far from optimal in ecological terms. An example is the migration of continental populations of [[Swainson's thrush]] ''Catharus ustulatus'', which fly far east across [[North America]] before turning south via [[Florida]] to reach northern [[South America]]; this route is believed to be the consequence of a range expansion that occurred about 10,000 years ago. Detours may also be caused by differential wind conditions, predation risk, or other factors.<ref>{{cite journal |author=Alerstam, Thomas |year=2001 |title=Detours in bird migration |journal=Journal of Theoretical Biology |volume=209 |issue=3 |pages=319–331 |url=http://www.mbfys.ru.nl/staff/j.vangisbergen/endnote/endnotepdfs/navigatie/Alerstam_detours_2001.pdf |doi=10.1006/jtbi.2001.2266 |pmid=11312592 |bibcode=2001JThBi.209..319A |url-status=dead |archive-url=https://web.archive.org/web/20150502060654/http://www.mbfys.ru.nl/staff/j.vangisbergen/endnote/endnotepdfs/navigatie/Alerstam_detours_2001.pdf |archive-date=2015-05-02}}</ref>

===Climate change===
{{Main|Climate change and birds}}
[[File:Saalfeld 2021 bird phenology.png|thumb|Differences in an Arctic shorebird species' phenology between a normal year and a hotter year.<ref>{{Cite journal |last1=Saalfeld |first1=Sarah T. |last2=Hill |first2=Brooke L. |last3=Hunter |first3=Christine M. |last4=Frost |first4=Charles J. |last5=Lanctot |first5=Richard B. |date=2021-07-27 |title=Warming Arctic summers unlikely to increase productivity of shorebirds through renesting |journal=Scientific Reports |volume=11 |issue=1 |pages=15277 |doi=10.1038/s41598-021-94788-z |issn=2045-2322 |pmc=8316457 |pmid=34315998|bibcode=2021NatSR..1115277S }}</ref>]]
Large scale [[global warming|climatic changes]] are expected to have an effect on the timing of migration. Studies have shown a variety of effects including timing changes in migration,<ref>{{cite journal |last1=Orellana |first1=J.M. |last2=Bautista |first2=L.M. |last3=Merchán |first3=D. |last4=Causapé |first4=J. |last5=Alonso |first5=J.C. |year=2020 |title=Shifts in crane migration phenology associated with climate change in southwestern Europe |journal=Avian Conservation and Ecology |volume=15 |issue=1 |pages=16 |doi=10.5751/ACE-01565-150116 |url=https://www.ace-eco.org/vol15/iss1/art16/ACE-ECO-2020-1565.pdf|doi-access=free }}</ref> breeding<ref>{{cite journal |author1=Jenni L. |author2=Kery M. |name-list-style=amp |year=2003 |title=Timing of autumn bird migration under climate change: advances in long-distance migrants, delays in short-distance migrants |journal=[[Proceedings of the Royal Society B]] |volume=270 |issue=1523 |pages=1467–1471 |doi=10.1098/rspb.2003.2394 |pmid=12965011 |pmc=1691393}}</ref> as well as population declines.<ref>{{cite journal |doi=10.1038/nature04539 |issn=0028-0836 |volume=441 |issue=7089 |pages=81–83 |last=Both |first=Christiaan |author2=Sandra Bouwhuis |author3=C. M. Lessells |author4=Marcel E. Visser |title=Climate change and population declines in a long-distance migratory bird |journal=Nature |date=2006-05-04 |pmid=16672969 |bibcode=2006Natur.441...81B |s2cid=4414217 |url=https://pure.rug.nl/ws/files/6695676/2006NatureBoth.pdf}}</ref><ref>{{cite book |author1=Wormworth, J. |author2=Mallon, K. |year=2006 |title=Bird Species and Climate Change: The Global Status Report version 1.0. |publisher=WWF |url=http://www.panda.org/about_wwf/what_we_do/climate_change/problems/impacts/species/cc_and_birds/index.cfm}}</ref> 

Bird migration is generally synchronised to take advantage of seasonal resources. For example, there is a strong link between seasonal migration and vegetation greenness in North America.<ref>{{Cite journal |last1=La Sorte |first1=Frank A. |last2=Graham |first2=Catherine H. |date=26 October 2020 |editor-last=Chapman |editor-first=Jason |title=Phenological synchronization of seasonal bird migration with vegetation greenness across dietary guilds |url=https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2656.13345 |journal=Journal of Animal Ecology |language=en |volume=90 |issue=2 |pages=343–355 |doi=10.1111/1365-2656.13345 |pmid=33107060 |issn=0021-8790}}</ref> Climate-induced shifts in the [[phenology]] of seasonal resource availability can cause mismatches between the timing of increased resource availability and important life-history events such as migration and breeding (aka [[phenological mismatch]] or phenological asynchrony).<ref name=":03">{{Cite journal |last1=Robertson |first1=Ellen P. |last2=La Sorte |first2=Frank A. |last3=Mays |first3=Jonathan D. |last4=Taillie |first4=Paul J. |last5=Robinson |first5=Orin J. |last6=Ansley |first6=Robert J. |last7=O’Connell |first7=Timothy J. |last8=Davis |first8=Craig A. |last9=Loss |first9=Scott R. |date=2024-03-19 |title=Decoupling of bird migration from the changing phenology of spring green-up |journal=Proceedings of the National Academy of Sciences of the United States of America |language=en |volume=121 |issue=12 |pages=e2308433121 |doi=10.1073/pnas.2308433121 |issn=0027-8424 |pmc=10963019 |pmid=38437528|bibcode=2024PNAS..12108433R }}</ref> These mismatches between the timing of resource availability and when organisms need additional resources may impact species’ [[Fitness (biology)|fitness]], as described by the [[Match/mismatch|match-mismatch hypothesis]].<ref>{{Cite book |last=Cushing |first=D. H. |title=Marine Ecology and Fisheries |date=1975 |publisher=Cambridge University Press |isbn=0521205018 |location=Oxford |language=en}}</ref>

In birds, individuals may use local temperature as a cue for migration. Changing temperature patterns due to climate change can result in [[population]]-level shifts in migration phenology.<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 of the United States of America |volume=118 |issue=28 |pages=e2026378118 |doi=10.1073/pnas.2026378118 |doi-access=free |issn=0027-8424 |pmc=8285904 |pmid=34260383|bibcode=2021PNAS..11826378B }}</ref> Such shifts in the timing of migration of hundreds of species are already detectable at the continental scale.<ref>{{Cite journal |last1=Horton |first1=Kyle G. |last2=La Sorte |first2=Frank A. |last3=Sheldon |first3=Daniel |last4=Lin |first4=Tsung-Yu |last5=Winner |first5=Kevin |last6=Bernstein |first6=Garrett |last7=Maji |first7=Subhransu |last8=Hochachka |first8=Wesley M. |last9=Farnsworth |first9=Andrew |date=16 December 2019 |title=Phenology of nocturnal avian migration has shifted at the continental scale |url=https://www.nature.com/articles/s41558-019-0648-9 |journal=Nature Climate Change |language=en |volume=10 |issue=1 |pages=63–68 |doi=10.1038/s41558-019-0648-9 |bibcode=2019NatCC..10...63H |issn=1758-6798|url-access=subscription }}</ref> While phenological mismatches appear to be more pronounced in long-distance migrants,<ref name=":03" /> certain species traits such as a [[Generalist and specialist species|generalist diet]] may help some species avoid more severe consequences of mismatches.<ref>{{Cite journal |last1=Mallord |first1=John W. |last2=Orsman |first2=Christopher J. |last3=Cristinacce |first3=Andrew |last4=Stowe |first4=Tim J. |last5=Charman |first5=Elisabeth C. |last6=Gregory |first6=Richard D. |date=31 October 2016 |title=Diet flexibility in a declining long-distance migrant may allow it to escape the consequences of phenological mismatch with its caterpillar food supply |url=https://onlinelibrary.wiley.com/doi/10.1111/ibi.12437 |journal=Ibis |language=en |volume=159 |issue=1 |pages=76–90 |doi=10.1111/ibi.12437 |issn=0019-1019}}</ref>