How do brids navigate during migration?

[Lisa!]

How do brids find their directions during migration? Do they have any natural compass in their brain?

 

[Danger]

I don't know too much about this, but they do have a magnetic organ which I believe is just above the base of the beak. There's also strong evidence that they can calculate things based upon the position of the sun.

 

[jim mcnamara]

birds do sense a magnetic field, e.g., thrush nightingales:
http://news.nationalgeographic.com/news/2001/11/1102_TVbirdflite.html
More general:
http://www.gi.alaska.edu/ScienceForum/ASF5/512.html

Research also cites a use of the sun and maybe stars as a secondary navigational aid.

 

[_Mayday_]

I guess this question is related, so I can understand why birds would migrate south, but then why do they have to migrate back up north again? What is not down south in the European Summer that is there in the European winter in other words?

 

[jim mcnamara]

Primary productivity in more Northern latitudes during summer is very high compared to the tropics - ie., more bugs, fish, and seeds for baby birds. Photosynthesis increases so much that there is a dip in atmospheric [itex]CO_2[/tex] during the summer months.[/itex]