Early bird tickets usually refer to discount tickets purchased within a certain period of time, and the price will be cheaper than regular tickets. Whether the fare difference needs to be paid depends on the specific fare policy and event arrangements. Generally speaking, if you purchase an early bird ticket, if the ticket price increases after the early bird promotion period ends, you may need to make up the difference before you can purchase it at the new ticket price. But there are also some events that may allow you to continue purchasing tickets at early bird prices after the promotion period ends. The specific situation needs to be judged according to the specific description of the event when purchasing tickets.