Almost a quarter of the little-spotted kiwi introduced to Shakespear Open Sanctuary are now dead.

A deadly disease has ravaged the little spotted kiwi population in an Auckland sanctuary, killing more than 10 per cent of the endangered birds at the park.

A total of 40 kiwi were moved to Shakespear Open Sanctuary in north Auckland in two batches, in March 2017 and in April 2018.

Since then five birds have died of avian malaria, with four others dying of other causes.

Renee Clayton Matt Maitland uses the radio transmitters to listen to their heart beats.

The 2017 kiwis were 10 females from Tiritiri Matangi Island and 10 males from Kapiti Island and all of the birds in 2018 were sourced from the Kapiti Island stronghold population.

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Auckland Council Senior Ranger Matt Maitland said avian malaria was fundamentally unmanageable in wild bird populations.

Bryan Lowe The first batch of kiwi bred successfully at the open sanctuary and none of the birds have been killed by predators.

All kiwi moved to Shakespear were assessed as fit for transfer prior to their move.

Massey University Senior Lecturer in Wildlife Pathology Stuart Hunter said avian malaria was caused by a parasite that invades red blood cells and other tissues, such as the liver, spleen, lungs and brain.

"The parasite is transmitted by mosquitoes," he said. "It is thought the parasite arrived in New Zealand with the introduction of non-native birds, such as the blackbird, who appear to carry the parasite without it causing any ill-health.

Delwyn Dickey Jonathan Miles of Auckland Council's biosecurity team puts a transmitter on one of the kiwi.

"Our native birds have little or no natural immunity to this parasite so it often causes severe and often fatal disease."

Department of Conservation (DOC) Principal Science Advisor Dr Hugh Robertson said kiwi translocations usually had good survival rates and DOC strived to maximise the health and wellbeing of the birds during this naturally stressful time.

"With the total remaining little spotted kiwi population in New Zealand being descended from as few as five birds, they possibly have a lowered immunity to diseases.

"Large scale translocations like this are intended to increase the overall population and genetic resilience of the species, and spread the risk in case of future large scale threats to birds on Kapiti Island, the main home of the species."

Shakespear Open Sanctuary Society Incorporated chair Peter Jackson said Shakespear volunteers were disappointed by the deaths.

"We are saddened by these unexpected deaths, however the remaining kiwi appear to be thriving and we are not aware of anything we could or should have done differently."

At the moment about 30 birds remained but there was some uncertainty as not all birds carry radio transmitters.

Maitland said health checks had taken place this week ahead of the breeding season in July.

"Four birds were located and recaptured on Wednesday, of these, three had made a 300g or greater weight gain (on transfer weights around the 1000g mark) and one had held stable.

"The birds look like they're in a great condition," he added.