Really good question...I believe this is big issue in India as no job/work in villages and people migrate frequently during particular session as they harvest crops and move to close by metro to earn money. The biggest challenge is in BUNDELKHAND REGION In INDIA and people are facing problem of drinking water. Villages are almost empty with huge migration in DELHI NCR.
I observed this issue from last 8-10 years and found an answer to dot he calculation using RAILWAY GENERAL CLASS TICKETS and MEETING IN GENERAL BOGI that too in JHANSI RAILWAYS STATION. that gave me rough estimation and few ideas.
Please let me know if you want more information.
Regards
Rajeev
NOW A DAYS i m DEALING WITH THE RESEARCH ABOUT SEASONAL MIGRATION OF kONKANA TRIBAL PEOPLE OF 5 TRIBAL TAHSIL OF NASHIK DISTRICT MAHARASHTRA. THESE ARE SEASONAL MIGRANTS . THEIR SPAN OF MIGRATION IS FRON OCT. TO APRIL. IMY PRAPOSED PH.D. WORK IS ON THIS TOPIC. IF YOU HAVE ANY MATERIAL OR EXPERENCE SHARE WITH ME IN FUTURE. WE WILL B IN CONTACT.
You could see the Migratory Intensity Index compiled by the National Population Council of Mexico
See the following link
http://www.conapo.gob.mx/swb/CONAPO/Indices_de_intensidad_migratoria_Mexico-Estados_Unidos_2010
http://www.conapo.gob.mx/es/CONAPO/Indice_Absoluto_de_Intensidad_Migratoria_Mexico_Estados_Unidos_2000-2010
http://www.conapo.gob.mx/es/CONAPO/Indice_Absoluto_de_Intensidad_Migratoria_Mexico_Estados_Unidos_2000-2010
http://www.conapo.gob.mx/swb/CONAPO/Indices_de_intensidad_migratoria_Mexico-Estados_Unidos_2010
It depends what you want to do and what data is available. . If you want to work mainly statistically then you might want to check, if migration is part of the questions asked in the census. Then you can calculate migration data from one to other censuses. In the end you have statistical data on how relevant statistically migration is, but you not necessarily know, what makes people migrate.
To learn about reasons, you better make interviews with migrants. These would be most likely immigrants, people who moved to the place where you conduct field work. This kind of research will be more qualitative in nature.