Si Racha, Thailand - Thailand's pygmy hippo Moo Deng marked her first birthday on Thursday as she grows out of the infancy which boosted her to worldwide internet fame.

Crowds have been invited to a four-day festival at Khao Kheow Open Zoo where Moo Deng – meaning "Bouncy Pork" in Thai – frolicked to stardom and amassed five million social media fans.

The first day of the extravaganza falls on a Thai public holiday and the agenda includes a lecture on Moo Deng's cheekiness, while a skincare beautician has paid $3,000 to sponsor her fruit-festooned cake.

Her handlers are also scheduled to auction off her belongings, but it's unclear what possessions Moo Deng has accumulated in her short life at the Chonburi province zoo a two-hour drive from Bangkok.

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There were hopes her stardom would spotlight the plight of the endangered pygmy hippo, native to West Africa with only around 2,500 left alive according to the International Union for Conservation of Nature.

But social media and search engine metrics suggest Moo Deng's popularity peaked around late September last year before dramatically declining.

"Moo Deng went viral very quickly when she was born," said Joshua Paul Dale, an academic who teaches courses on the phenomenon of "cuteness" at Japan's Chuo University.

"Maybe part of our appreciation of cuteness is knowing that it's something that doesn't last very long," he told AFP.

Moo Deng's blubbery rose-blushed face launched a thousand memes and a plethora of merchandise including piggy banks, party shirts, and popsicles – prompting her owners to trademark her likeness.

The pint-sized pachyderm quadrupled ticket sales for the zoo as people flocked to see her small and sparse enclosure, which was once even broadcasted by a 24/7 livestream.

Moo Deng is part of a pantheon of captive animals who have enjoyed flash-in-the-pan popularity for their cuteness online, including Australia's Pesto the penguin, China's Hua Hua the panda, and Scotland's Haggis the hippo.

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Pygmy hippos have a lifespan of between 30 and 50 years.

While academic Dale predicts she may lose the limelight to longevity, he says Moo Deng could enjoy enduring appeal as fans recall "how unbearably cute she was when she was very, very small and just born".

"That can kind of continue on and affect our relationship with cute things, even when they grow up," he said.