How do birds know when to fly south and when to return?

Answer 1

They are genetically programmed.

Answer 2

it could be a number of things:

patterns of stars,

watching older birds fly south and copying what they've done,

if they're dark birds and they're in an area that snows (the north), they could stand out to predators if they don't fly to an area without snow (the south) where they can blend in better

following food - in the winter in cold areas, there's not as much food so they fly south where weather is warmer and food is more abundant

and also if they're water birds (like geese), the water gets cold in the winter, so they move to areas where the water is warm so they can swim!

Answer 3

The truth is that nobody knows. But you can just as easily ask "How do you know it is fall?"

Climate, position of the Sun, Stars, condition of the foliage...there are a number oyf clues that they could be keying on...

I think a more interesting question is WHY do they migrate? I live near NYC and everywhere there is a manicured lawn there are flocks of Geese that stay all year round and graze like cattle...If they aren't driven to migrate then is it just learned behavior?

Answer 4

Birds migrate to find food, not to stay warm. They instinctively know when to go when the food is not available & they know which way to fly to look for food because of their internal instincts.

Answer 5

They have a special weather department that tells them so.

They get in on a special BBC (Bird Barnstorming Channel) radio

Answer 6

cold=south, hot=north

Answer 7

their sensitivity whenever climate changes,, if your talking about the migratory bird,,

Answer 8

because the nutura characteristic

Answer 9

they're internal body clocks.