Photo/Illutration A staff member of Adventure World dressed like a parent penguin tries to feed an emperor penguin chick through a syringe in Shirahama, Wakayama Prefecture, on Oct. 2. (Hiroshi Ono)

SHIRAHAMA, Wakayama Prefecture--At first glance, aquarium staff here appeared to be engaged in a bizarre cosplay act involving an emperor penguin chick.

But the employees, wearing penguin costumes, were actually on a scientific mission.

As the Adventure World aquarium has learned, emperor penguin chicks raised by undisguised humans do not mate after being reunited with their real parents.

So they hoped the chick would be duped into thinking that it was being raised by penguins, not humans, and would later breed.

The recently hatched chick of the world’s largest penguin species is the 13th born at the aquarium.

The chick’s real mother, a 21-year-old, laid the egg at the aquarium on July 26. The egg was then transferred to an incubator to prevent it from being crushed by the nearly 40-kilogram parent.

The egg was seen moving in mid-September, and the chick tried to break out on Sept. 29. It emerged from the shell on Oct. 1, weighing 300 grams.

But it had to be raised by humans to ensure its survival for an eventual return to its real parents.

Adventure World hatched the first emperor penguin chick in Japan in 2004. And since 2012, the aquarium has been making efforts to return chicks to their parents after they grow to some extent.

Birds view the first moving things that they see as their parents. The aquarium found that the emperor penguin chicks that recognized humans as their parents do not mate after growing to adulthood, effectively ending the desired breeding cycle of penguins at the aquarium.

To raise the latest chick, staff members wore a penguin-shaped mask and a special left-handed glove resembling the head of a parent penguin.

Without saying a word, they fed the chick liquid food comprising mashed herring and krill five times a day with the chirping of the parent birds playing in the background.

In one earlier case, it took as long as three months for the parent birds to accept the returned chick as their own offspring and start feeding it.

Last year, the acceptance period was shortened to eight days, according to Adventure World officials.

The penguin species is also kept at the Port of Nagoya Public Aquarium in Nagoya, but Adventure World is the only facility in Japan that has succeeded in breeding emperor penguins.

Shota Sato, 32, an Adventure World staff member, explained the difficulty in keeping the bird species.

“Emperor penguins have larger bodies and are thus smarter, so they do not easily recognize chicks that have once been taken away from them as their offspring,” Sato said.

The new penguin chick went on display at Adventure World on Oct. 5 and was returned to its parents on Oct. 21 after its weight topped 500 grams.