WELLINGTON, New Zealand — The wayward penguin known as "Happy Feet" is missing in the Southern Ocean.
Experts tell The Associated Press the most likely scenario is that the emperor penguin's satellite transmitter fell off. The small unit was attached to his feathers with super glue and was designed to fall off when he molted early next year.
But the unit stopped transmitting Friday, just five days after the penguin was released into the sea south of New Zealand.
Other possibilities are that Happy Feet was eaten by an orca or a leopard seal; that he died of natural causes; or that the transmitter malfunctioned.
The aquatic 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 repeatedly flushed his stomach to remove sand and fattened him up on a diet of fish.
After he was released from the deck of a research vessel, Happy Feet's satellite tracker showed that he swam in a meandering route, ending up about 75 miles (120 kilometers) southeast of where he began when the last transmission was received Friday morning. Experts say his looping pattern was typical for a penguin chasing fish.
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."
That's the scenario favored by Peter Simpson, a program manager at New Zealand's department of conservation.
"Who knows? He's probably swimming along quite happily without a transmitter on his back," Simpson said.
"I'm still confident we did the right thing by releasing him back into the wild," Simpson added. "He's a marine bird and he's designed to swim and he's designed to live in the ocean."
Scientists say there's an outside possibility they may again hear from Happy Feet. The penguin also has been fitted with a transponder chip under his skin, similar to those used to identify household cats and dogs. The chip will 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."