So far the kiwi has had several weeks of care, including several pedicures to clean the nail and bone, x-rays and blood samples.
"This kiwi is such a fighter.
We are happy to report the little superstar is eating well in hospital and after the first week, when it was touch and go, he has started to venture around his room, exercise, forage and gain some much needed weight.
"But it's going to be a long journey," Nijman says.
It will be several weeks before Wildbase vets will know if the kiwi has a chance of long-term survival.
If he can be released back into the wild, DoC will liaise with iwi on arrangements.
How the battered bird got into the culvert in early August remains a mystery, but he owes his survival to two roading inspectors from infrastructure company Downer.
Downer junior network inspector Logan Turner was with his colleague Isaak Ryan inspecting culverts on behalf of Waka Kotahi on State Highway 3 near Tongaporutu.
At first glance Ryan didn't spot the beleaguered bird, but the pair were surprised when a second look revealed the kiwi and its plight.
"It was the first time I'd seen a kiwi in real life, so it was pretty cool. I have never come across wildlife while inspecting culverts before," Turner said.
After contacting their supervisor, the two men called the Doc Hot Line and offered information on the tools needed to remove the metal grate and access the bird.
DoC ranger Alison Evans then got into the sump leading off the culvert and plucked the kiwi from its predicament.
"It didn't have any objection to being picked up and seemed almost relieved to be rescued.
"It was underweight, cold and suffering from exhaustion," Evans said.
"The culvert was a pretty inhospitable place to be imprisoned, with large trucks travelling past at open road speeds only a few metres away and water at the bottom of the sump."
If people discover kiwi stuck in holes, drains or culverts – and the bird appears unable to get out – DoC recommends using a plank of some kind to create a ramp for the bird to climb on.