Migration is triggered mainly by:
photoperiod reflects key principle in quiz on animal behavior+pyqs, where evolutionary mechanisms shape genetic variation and adaptation. In this context, photoperiod aligns with experimental and theoretical evidence from population genetics, behavioral ecology and molecular phylogeny. Textbooks like Campbell Biology, Futuyma Evolution and Hartl Principles illustrate supporting data. Understanding why photoperiod fits helps integrate natural selection, environment.
Ref: Alcock, Animal Behavior, Kin Selection and Social Behavior.