What is Migration?
:''For people see [[Human migration]]; for data see [[Data migration]]''. [[File:Connochaetes taurinus -Wildebeest crossing river -East Africa.jpg|thumb|300px|[[Wildebeest]] crossing river in [[East Africa]]]] '''Migration''' is when [[animal]]s move on a regular cycle. For example, [[caribou]] in the [[Arctic]] go south in winter and return in [[summer]] when it is warmer. Migration is the travelling of long distances in search of a new [[habitat]]. The [[wikt:trigger|trigger]] for the migration may be local [[climate]], local availability of food, or the [[season]] of the year. To be counted as a true migration, and not just a local dispersal, the movement should be an annual or seasonal event. Many [[bird]]s migrate to warmer places for the winter, as do some [[insect]]s such as the [[migratory locust]]. Young Atlantic [[salmon]] leave the river of their birth when they have reached a few inches (cm) in size.<ref name=Att>{{cite book|title=The trials of life|url=https://archive.org/details/trialsoflifenatu0000atte_a3v0|author=David Attenborough|year=1990|isbn=0002199408|publisher=Collins / BBC Books|location=London|page=[https://archive.org/details/trialsoflifenatu0000atte_a3v0/page/123 123]}}</ref> Many species in the sea have a daily migration. [[Plankton]] go up for the day where there is light, and down at night, where they are less easy to find. The many species which feed on them follow them up and down. Migration is an [[evolution]]ary force. This is because it is a major source of [[natural selection]]. The success of migratory animals to make the journey is usually needed for them to reproduce. Many parts of the world have a strongly seasonal [[climate]]. In order to survive, many species need to breed in one place and, later, eat in another place. The simplest example is the African [[herbivore]]s, who follow the growth of [[grass]] in [[East Africa]]. This region has seasonal [[rainfall]], and so it has seasonal growth of grass. Their [[predator]]s follow them.<ref name=Att/> == Bird migratio