Animals migrate when they need different habitats for different stages in their life-cycle. This behaviour has evolved (is evolving) and has a genetic basis, leading to variability in the ‘migration strategies’ of individuals. Presumably individuals who ‘choose’ not to follow their species normal migration pattern will not breed as successfully as those who do when things remain ‘normal’, but if environmental conditions change then these aberrant individuals might well be more fortunate and go on to initiate new migration patterns.
When the environment changes on a ‘geological’ timescale species will have the time for natural selection to alter their migration behaviour, but problems arise if the changes are too rapid. Mankind is affecting the environment in many ways (see ‘Human Effects’), and often changes are too fast to allow species to adapt.
While it is true that some mammals can learn migration routes from their elders invertebrates and fish can not. Migration (and therefore navigation during migration) is instinctive. In other words navigation must have a genetic basis and take many generations to change by evolution. Invertebrate navigation must depend on environmental ‘clues’ which remain constant over very long periods of time: such as magnetic fields; position of the sun, moon and stars; direction of prevailing winds etc. Exactly how these are used is poorly understood.
Other articles by John Blatchford