Monarch butterfly migration is the phenomenon, mainly across North America, where the subspecies Danaus plexippus plexippus migrates each summer and autumn to and from overwintering sites on the West Coast of California or mountainous sites in Central Mexico.

Source : Wikipedia

Roughly half a million Monarch butterflies migrate each year, but no individuals make the round trip. Four generations are involved in the annual cycle, so there is no possibility of the offspring somehow 'learning' the route. It is currently unknown how they navigate (or how they judge the correct timing). One theory is that they may be somehow 'marking' the route with chemical odours.

Further info: monarchwatch.org

Also see :The Sardine Runplugin-autotooltip__plain plugin-autotooltip_bigThe Sardine Run

"The term ‘sardine run’ is part of the cultural heritage of the South African nation and refers to a natural phenomenon that is well known to the general public but still poorly understood from an ecological perspective. This lack of understanding has stimulated numerous hypotheses, often contradictory, that try to explain why (ultimate factors) and how (proximate factors) the run occurs. and Bogong moth migrationplugin-autotooltip__plain plugin-autotooltip_bigBogong moth migration

"The Bogong moth, Agrotis infusa, has a nocturnal lifestyle and migrates from the Darling Downs in southern Queensland [Australia] to the Snowy Mountains in southern New South Wales where, in a single cave several hundred thousand of Bogong moths can aestivate, a form of hibernation in the summer during the dry period. After summer has passed the moths emerge again and migrate back to their breeding grounds in Southern Queensland. After laying eggs they die and the next g…