The annual wildebeest migration takes place over the course of the year and it can be difficult to track their exact movements and then plan your safari holiday to coincide. This site tries to do the impossible by tracking their movements across the Serengeti and the Masai Mara;
http://wildebeestmigration.blogspot.com/
Above is an example of the quality of their tracking maps. The site only updates when the herds move a significant distance, so at times the updates can be slow.
For more information on safaris in the Masai Mara, Serengeti and the Wildebeest migrations visit the African Travel Experts
African Holidays Blog 