Animal Kingdom was introduced to Walt Disney World on Earth Day, April 22, in 1998 and each year those two special events have been celebrated with lots of activities. 2013 will continue in this tradition with its Party for the Planet throughout the park.
http://www.themouseforless.com/tripplanning/wdwparks/annual/Apr-JunEventsED.shtml
http://land.allears.net/blogs/dnews/2013/04/animal_kingdom_15th_anniversar_1.html