WELLINGTON - Nothing has been heard for several days from a young Emperor penguin released last week after capturing global attention when it washed up on a New Zealand beach thousands of kilometres from home.

The bird, nicknamed "Happy Feet" by locals, was released into the southern ccean on Sept 4 from a New Zealand research ship and had been tracked since then by means of a GPS transmitter that showed it heading southeast.

But no transmissions have been received since September 9, said Sirtrack, a wildlife tracking firm that had been following Happy Feet.

"This indicates that the satellite transmitter has not broken the surface of the water, required to transmit, since that time," the company said on its website, noting that the transmitter had been working correctly when last heard from.

"This leads to the conclusion that either the satellite transmitter has detached or an unknown event has prevented Happy Feet from surfacing."

The bird became the focus of the media after it turned up on a beach some 4,000 km (2,500 miles) from its home, only the second Emperor penguin known to have shown up in New Zealand.

It underwent endoscopic surgery in June to remove three kg (6.6 pounds) of sand from its stomach and subsequently recuperated at the Wellington Zoo, its every move monitored by a "penguin cam" that let fans watch it around the clock.

Penguins normally eat snow to stay hydrated but veterinarians believe Happy Feet, named after the main character in a popular animated film, became confused and ate sand instead.

It travelled back to the southern ocean in a specially designed crate and tumbled down a tarpaulin ramp to freedom on Sept 4, fitted with the transmitter and a transponder under his skin.

Colin Miskelly, curator of terrestrial invertebrates at the Museum of New Zealand Te Papa in Wellington, said in a blog post that while solar flare activity had initially been blamed for the silence, that did not appear to be the case.

"It is unlikely that we will ever know what caused the transmissions to cease, but it is time to harden up to the reality that the penguin has returned to the anonymity from which he emerged on 20 June," he said.

"Maybe, just maybe, he will surprise us all by turning up at a monitored Emperor penguin colony, where the transponder inserted under the skin on his thigh will remind us all that once upon a time, a long time ago, he was more than just another penguin."