The chobo symbols change throughout the day.

They do not represent how many people are registered on a server, but how many people are online at one time in a one area.

The chocobos will change depending on the time and day. Since each server has different Na/Eu/Jp populations.

As far as I know there is no sites that record the server traffic.

Cornelia is semi crowded in Uldah you will not get into Behest in Uldah camps at certain times in the day. Outside that it is not more crowded then the lowest population server though. Atm the only populated place in the game for anyone seems to be uldah.