Evolution of migration

Eg

• Benefits associated with migratory flights must be greater than those associated with staying in Alaska and having to tolerate seasonal changes.
• Selective advantage linked to evolution of migration e.g. reduction in competition; improved environmental conditions; greater reproductive success must have resulted from selection for migration.
• Evolution of migration is linked to the improved survival of the species, despite the energy requirements of the migratory journey.
• Consideration of such factors as range expansion due to competition and / or changing environmental conditions, increased breeding success at fringes of range (but return to seasonal feeding grounds during non-breeding season), or accidental, eg blown off course.
• Increasing selection for those birds that possessed physiological responses to environmental cues for migration, eg birds that depart before food availability, photoperiod or temperatures decrease.
• Similar pressures at new destination forced migratory populations / birds back to origin.
• May have occurred when landmasses were joined / closer together, flight distances shorter, staging sites more frequent. Continental drift then selected those best adapted for longer flights.