The emperor penguin taken from Peka Peka beach is to undergo surgery tomorrow, with zoo staff giving it a 50 per cent chance of recovery.
'Happy Feet' was earlier taken to Wellington Zoo in a chilled box from the Kapiti Coast after the penguin's behaviour changed markedly in the last few days.
Veterinary staff at the zoo said the bird was dehydrated and was suffering from heat exhaustion.
It needed to be stabilised before being operated on, but would this afternoon undergo a manual procedure to try to clear its throat, which seems to be blocked.
The penguin was put under anaesthetic this afternoon while vets flushed sand out from inside its body.
Wellington Zoo vet science manager Lisa Argilla said he was a spirited bird and the team was doing their best for him.
"He's still strong and he's got a lot of fight in him, which is good," Argilla said.
"Every animal is important to us. We don't really want him to suffer.
"I'm hoping its just a piece of driftwood that we can reach down and pull out."
As for the future, the zoo was still discussing the best course of action with the Department of Conservation (DOC).
While the best solution would be a return to Antarctica, there was also a facility in the USA which deals particularly with emperor penguins.
Returning the bird to Antarctica was not feasible because there was no transport there in winter and experts advised that large birds could suffer trauma if transported long distances.
Zoo staff said the last emperor penguin to come to New Zealand was released in Foveaux Strait.
DOC biodiversity manager Peter Simpson said the penguin had been eating sand, which may have been an effort to cool itself down, as penguins normally eat snow if they get too hot.
Simpson said it had become lethargic and that it might have an infection from eating sticks.
The bird was first spotted on Peka Peka Beach on Monday afternoon by resident Chris Wilton, who nicknamed it Happy Feet, and has since attracted local and global interest.
A cordon was put up around the penguin during the week, keeping people about 40m away due to high numbers of sightseers, with a group of residents even keeping guard on the beach overnight.
Kapiti Coast District Council also assigned a security guard to prevent harm to it.
It is the second recorded incident of an emperor penguin on New Zealand shores.
- Michelle Duff, The Dominion Post and Stuff
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