Cara the Chimp undergoes surgery

Anaesthesiologist Dr. Kerrie Lewis (right) and surgeon, Dr Rebecca Garland operating on Cara. Photo / Supplied

A 33-year-old chimpanzee at Wellington Zoo has undergone major ear surgery after rejecting a custom-made plug to prevent her from inserting sticks and pieces of straw into her ear.

Plagued by persistent infections, Cara had her right ear canal removed by ear, nose and throat surgeon, Dr Rebecca Garland at The Nest Te Kōhanga, the zoo's animal hospital.

"Surgery went smoothly, and we were able to patch up Cara's ear," said Dr Garland.

"As with humans, the resulting loss of hearing after having both ear canals removed will be approximately 60 per cent."

But a hearing test done while Cara was anaesthetised showed that her level of hearing had already been compromised.

Cara, who has lived at the Zoo since 1992, for years suffered from a chronic infection in her left ear that couldn't be resolved by oral antibiotics.

It became life threatening when it spread into her inner ear and part of her skull so surgery was performed in 2010 and the infection as cured.

But last year, it was discovered she had a new infection in her right ear.

In September, she underwent surgery and a custom-made plug was inserted to prevent Cara from inserting sticks and pieces of straw in her ear.

Cara has lived at Wellington Zoo since 1992. Photo / Supplied

But the clever primate was not a fan of her new ear accessory and found a way to remove the plug shortly after waking up from general anaesthetic. And she kept using objects to relieve the pain.

The zoo is hopeful her follow-up surgery is a success.

"Animal welfare is our number one priority at Wellington Zoo," said Dr Lisa Argilla, the zoo's manager of veterinary science.

"We have been able to treat Cara's symptoms to make sure she is comfortable, and we have tried innovative techniques to save her ear - but this surgery means she won't be able to have an ear infection ever again."

Paul Horton, life science manager at Wellington Zoo was positive about Cara's recovery and reintegration with other primates.

"Chimpanzees communicate primarily through gestures, body postures and facial expressions, as well as some vocalisations.

"Cara's hearing has been impacted for some time without impacting her status among the other chimpanzees.

"Knowing that she had already lost a significant level of hearing and had still functioned well within the group means we can be confident that she can be integrated back into the group without issue."

Dr Craig Johnson, Professor of veterinary neurophysiology at Massey University, evaluated Cara's hearing ability before surgery.

The information gives the keepers who care for Cara a good indication of how she will integrate back into the troop of chimpanzees.