Answer :
Answer:
Combination of events
Explanation:
Migratory birds tend to leave and return to their biological niches on the change of weather patters. The reason for these changes are a combination of events. Firstly the changes in day, night hours will initiate migration patterns. Next the birds will experience changes in food availability and will tend to follow food availability. Finally, genetic predisposition causes these migratory birds to follow migratory patterns and observe this behaviour over generations.