Disney's Animal Kingdom turns 21 today. But Disney (DIS 1.54%) won't celebrate the Earth Day birthday of its animal-based theme park the way it did last year. Disney loves round-numbered milestones. However, now that the park has hit Florida's legal drinking age, it does lead one to wonder what the next 21 years will bring for Disney World's youngest park.

Disney is in the process of beefing up its gated attractions, and several new rides and experiences will be coming to Disney World between now and late 2021, when the resort turns 50. Again, Disney has a thing for round numbers. Three of Disney World's four theme parks will be getting major additions in the next two years and change. The lone holdout -- for now -- is Disney's Animal Kingdom. 

A family walking through Pandora -- The World of Avatar at Disney's Animal Kingdom.

Image source: Disney.

Wild thing

A lot has changed since Disney's Animal Kingdom made its debut on Earth Day 1998. The park didn't get into a groove right away, with controversy leading up to its grand opening. There were animal fatalities as it populated its exhibits, and Disney had to tone down graphic poaching imagery on its flagship safari ride during previews. Attendance declined for three consecutive years after its first full year of operation, and it wasn't until it added Disney World's tallest roller coaster that it finally resonated with park guests. Now, the park that opened without a single sit-down restaurant has two. 

The 2017 addition of Pandora -- The World of Avatar helped catapult the park from third to second in terms of Disney World annual attendance, but those days are numbered. Disney's Hollywood Studios should be a pretty consistent silver medalist once its Star Wars-themed expansion opens in late summer, building on the momentum it started with the introduction of Toy Story Land and the slated opening next spring of Mickey & Minnie's Runaway Railway. Epcot initially brings up the rear, but it won't stay in fourth place once the Guardians of the Galaxy indoor roller coaster and Ratatouille dark ride open. The original Magic Kingdom park has never come close to losing its pole position as Disney World's top draw, but Disney's busiest park will become even more popular when its neon-illuminated Tron Lightcycle Power Run coaster opens in 2021. 

When Disney World announced its ambitious four-year plan for new rides in the summer of 2017 ahead of Disney World's 50th anniversary, it was only Disney's Animal Kingdom that wasn't slated for a new e-ticket addition. It had opened its Pandora-themed expansion just a couple of months earlier, but it was odd to see Disney not try to cash in on the animal park's momentum. Two years later, and we're still left wondering what the park's next act will be.

Theme parks are a big part of Disney's business. It's the media giant's most consistent segment, and given the volatility with its theatrical releases and the uncertainties of its media networks juggernaut, this is the smoothing agent for its otherwise lumpy financials. There are enough new things coming to Disney World's other three parks to lock tourists in for the next few years, but neglecting the fourth seems dangerous. With so many things going right for Disney these days -- and the stock at all-time highs -- it can't afford to let any part of its Florida empire meander at a time when its biggest rival is about to announce plans for a major resort expansion.

The next 21 years for Disney's Animal Kingdom will be as successful as the world's leading theme park operator lets it be.