Question

why do the birds move their nack often

Answer 1

Hello friend,
Birds often move their neck for wide field vision purpose.
hope it helps.

Answer 2

Hey there!

As we know now a days people kill birds with their guns. Birds move their neck often for their protection. It makes them aware if any danger will be there. If any hunter came to shot them then they fly high in the sky. 

Hope it helps you!