Editing Reverse migration (birds) (section)

== Reverse migration as genetic or learned behaviour ==
Some large birds, such as [[swan]]s, learn migration routes from their parents. However, in most small species, such as [[passerine]]s, the route is [[gene]]tically programmed, and young birds navigate innately to their wintering area.<ref name=":4">{{Cite journal |last=Rees |first=Eileen C. |date=September 1989 |title=Consistency in the timing of migration for individual Bewick's swans |journal=Animal Behaviour |volume=38 |issue=3 |pages=384–393 |doi=10.1016/s0003-3472(89)80031-4 |issn=0003-3472}}</ref> 

As migration is most often genetically programmed before birth, there can be rare variations and defects that change the migration programming. These variations will account for some but not all reverse migration cases. Birds that have changed their migration path, if they survive, may breed with others who also follow this different migration route. Their offspring and subsequent generations may now follow the new, genetically programmed migration route.<ref name=":3">{{cite journal |last1=Gilroy |first1=James J. |last2=Lees |first2=Alexander C. |date=September 2003 |title=Vagrancy theories: are autumn vagrants really reverse migrants? |url=http://britishbirds.co.uk/wp-content/uploads/article_files/V96/V96_N09/V96_N09_P427_438_A003.pdf |journal=British Birds |volume=96 |pages=427–438}}</ref> 

Genetic variations may be triggered by a range of factors, including mutations in the genes responsible for the sensing of environmental cues such as photoperiod (day length) or geomagnetic fields, which birds use for navigation. Other factors, such as changes in habitat availability, food sources, or climate conditions, may also contribute to changes in migration patterns. These genetic and environmental influences can lead to the rare but intriguing phenomenon. 

[[File:Motus (radiotracking) 02.jpg |thumb |188x188px |A station like this can be used to track transmitters on birds.]]