Light, temperature, a velocity of the wind, etc. affect bird migration.
When birds consume more amount of food, the fats deposited under subcutaneous layer affects the nervous system, then, the birds migrate towards the breeding place.
Biological or Hormonal factor
Due to the intensity of light, the pituitary gland stimulated which secretes the gonadotrophic hormone (FSH and LH). These hormones activate gonads which affect nervous system then the birds migrate towards breeding place.
Shortage of food
In the northern hemisphere, due to ice sheet during winter, shortage of food occurs. So, the birds migrate towards southern hemisphere.
Latitudinal migration: North to south and vice-versa. Eg; Siberian crane.
Longitudinal migration: East to West and vice-versa. Eg; Starling bird.
Vertical migration: Up and down in the mountainous region. Eg; Daphe.
Partial migration: Within a single species, some do migrate and some do not. Eg; birds of the temperate region.
Irregular migration: Migrate in all direction covering few or many miles. Eg; Herons.
Regular migration: Birds came out from their nest in the morning to search food and return back in evening hour daily. Eg; Pigeon, Sparrow.
Seasonal migration: Some birds are winter visitors like snow bunting whereas some birds are summer visitors like swift.