The penguin known as "Happy Feet" has vanished in the ocean on his way home from New Zealand, eluding his trackers just days after his release and leaving behind a mystery that may never be solved.
After seizing global celebrity by going off-course and landing on a New Zealand beach far from its Antarctic abode, the emperor penguin has simply disappeared from the grid.
Happy Feet's satellite transmitter went silent Friday, five days after experts released the bird from a research ship into the Southern Ocean about a quarter of the way down to Antarctica.
Initial dispatches from the device showed that Happy Feet swam in a meandering route, ending up about 75 miles (120 kilometers) southeast of where he began by the time the last transmission came across Friday morning. Experts say his looping pattern was typical for a penguin chasing fish.
At this point, the transmitter may have simply fallen off, experts tell the Associated Press. It was attached to the bird's feathers with super glue and was supposed to fall off anyway early next year when he molted.
"Who knows? He's probably swimming along quite happily without a transmitter on his back," said Peter Simpson, a program manager at New Zealand's department of conservation.
Or, he may have died of natural causes.
Or, something more sinister: Happy Feet could have been eaten by an orca or a leopard seal.
Scientist likely will never know.
But there's a tiny chance they could get more clues one day because of another, small device implanted under the bird's skin. This transponder chip could send a signal if it comes close enough to an Antarctic monitoring site, but that might take years.
Named after the penguin odyssey film "Happy Feet," the bird was discovered on a New Zealand beach in June.
He became sick from eating sand which he likely mistook for snow, but was nursed back to health over two months at the Wellington Zoo. Veterinarians, who determined the bird's gender, repeatedly flushed his stomach to remove sand and fattened him up on a diet of fish before he was released back into the ocean Sept. 4.
Kevin Lay, a consultant at the company Sirtrack, which attached the tracking device, said staff have gone over diagnostics from the tracker and it appears it was functioning well until the last transmission.
Lay said the tracker needs to be above the water's surface to transmit. Because penguins surface regularly to breathe, that hadn't proved a problem until Friday.
"We think the most likely scenario is tag detachment," Lay said. "The intention was always that the transmitter would fall off."
Simpson said he was still confident that releasing Happy Feet was the right thing to do.
"He's a marine bird and he's designed to swim and he's designed to live in the ocean," Simpson said.
Scientists say there's an outside possibility they may again hear from Happy Feet because of the implanted transponder chip, similar to those used to identify household cats and dogs. The chip could be activated if the penguin turns up near certain monitored emperor colonies in Antarctica.
Because Happy Feet is believed to be about 3 years old, it could be a year or two before he would arrive in an Antarctic colony to breed _ if he is still alive.
New Zealand penguin expert Colin Miskelly said it's time to face facts.
"It's unlikely that we will ever know what caused the transmission to cease," Miskelly wrote on his blog. "But it is time to harden up to the reality that the penguin has returned to the anonymity from which he emerged."