By Kim Griggs
If you are a bird that does not fly, having two legs is pretty important.
Currently, Tahi can only hop around
So when a wild kiwi lost one of his legs below the knee to a gin trap, a New Zealand zoo decided to help out this iconic native bird.
"The bird gets around well enough (by hopping) but he won't be able to breed with one leg," says Gerry Whitehouse-Tedd, an animal training and conditioning specialist at Wellington Zoo where Tahi - Maori for "one" - lives.
The zoo decided to see if it could fit a prosthetic leg to the North Island brown kiwi.
"For this particular sub-species of kiwi, he is an important bird," says Mr Whitehouse-Tedd.
Film star treatment
For help, the zoo turned to its neighbours - the Wellington Artificial Limb Board and the Weta Workshop, makers of special effects for movies such as Lord of the Rings and King Kong.
To create a mould of the bird's stump, Gino Acevedo, prosthetic and visual creature effects art director at Weta Workshop, used the same techniques on the kiwi as he would on a film star.
Tahi was anaesthetised while a cast was taken
"When we take a face cast of actors, such as when we have to duplicate someone like Christopher Lee or Ian McKellen to make a nose, we have to be able to see all the pores and detail so we can match it exactly onto the actual prosthetic," says Acevedo.
So with the bird anesthetised to prevent any distress, Mr Acevedo coated the kiwi's stump in alginate, the same material orthodontists use for taking casts of teeth.
After the alginate set, the leg was released and Acevedo then used casting plaster to make a mould which the prosthetic makers could use.
"So, whatever prosthetic [the technician] would make, it would fit the stump exactly," says Acevedo.
The mould was an exact replica of Tahi's leg
Armed with the Weta moulds, which replicated everything exactly, right down to the kiwi's rough, scaly skin, Peter Allen from the Wellington Artificial Limb Centre set about making an artificial leg for the kiwi.
Without the usual communication he would have with a human customer, Allen resorted to videos to figure out just how to mimic the kiwi's gait.
"I spent two or three hours looking at the videos trying to see what the leg does.
"I'd find a segment that showed me the information, and then I would freeze it and frame advance the video to see (the) angles - in the different parts of the joint."
The prosthetic limb is articulated
Because of the way the kiwi bends its leg when running and sitting, Allen decided to make Tahi an articulated prosthetic.
"There are no prosthetic components that make joints this small; they just don't exist. So I scrounged around for little bits and pieces of metals, pins, bits of tube and recreated the joint," he said.
Taking the next step
The test for the work's success came when Tahi tried the limb for the first time. Standing was no problem for the kiwi, but when it tried to run, the leg buckled too much.
Its keepers think this is caused by the strength the flightless kiwi has in its legs.
"Their legs are actually so strong because it's part of their defence mechanism as well," says Annemieke Timmermans, an assistant animal trainer at Wellington Zoo.
"They'll roll over and kick out with their legs."
The next stage is to adjust the leg so that it is less flexible, enabling Tahi to run on it.
The aim is for Tahi to be able to run with the limb
The zoo's Gerry Whitehouse-Tedd is full of praise for the experts who have volunteered their help to the zoo.
"It's definitely one of the best false legs I've ever seen for a bird or for any animal," he said.
And if it works, there are plenty of other New Zealand native birds who would benefit," added Mr Whitehouse-Tedd.
"This is not the only bird in New Zealand with one and a half legs. There are many, many more out there and there will be as long as people set [gin] traps."