It may have been a damp day but spirits were high at the release of 20 little spotted kiwi at Shakespear Open Sanctuary.

They are our tiniest kiwi and as from April 29 little spotted kiwi are making a new home at the Shakespear Open Sanctuary in North Auckland.

Air New Zealand passengers flying north to Auckland were given a special treat sharing the flight with the feathery VIPs who were travelling free of charge. And while it was a damp day when they arrived, spirits were high.

Weighing around one kilogram, females lay the biggest egg in relation to their size of any bird in the world.

Kimberley Collins Zealandia Reserve in Wellington had one of only two mainland populations of little spotted kiwi.

That's the eye-watering equivalent of your mother giving birth to you when you were six years old.

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Outside of Zealandia Wildlife Sanctuary in Wellington, with around 140 of the birds, and Cape Sanctuary on Cape Kidnappers in Hawke's Bay, Shakespear Regional Park now have the only other mainland population in the country behind their 1.7 kilometre predator proof fence.

The fence from Army Bay to Okoromai Bay encloses around 500 hectares and cost $750,000 seven years ago.

Unlike bigger North Island brown kiwi that are able to fight off pests like stoats and cats, once they reach around one kilogram in weight, many spotted kiwi never reach that milestone making them much more likely to be killed in the wild.

The size of a bantam the kiwi were a popular meal for early Maori and then Europeans. There was also a regular trade in skins with large numbers collected for European museums. Add cats, dogs and stoats to the mix, and the kiwi were all but wiped out by the 1900s.

A remnant population survived on Kapiti Island. After management and with numbers around 1,400 birds, Kapiti Island is now at capacity. A few survived on D'Urville Island in the Marlborough Sounds, but have since died out.

Until recently these kiwi were only able to be trans-located to five other islands.

"With island sanctuaries now at capacity, this new mainland population of kiwipukapuka is critical to their survival," DOC translocation project manager Angus Hulme-Moir said.

"And it reflects the great work Auckland Council and the Shakespear Open Sanctuary Society have done to create this predator free sanctuary, providing a safe habitat for these birds,"

Sixteen birds initially moved onto Tiritiri Matangi Island, just 3.4 kilometres from Shakespear at the end of the Whangaparaoa Peninsula. Since the 1990s the population has grown to around 80 birds.

Also a working farm, all farm dogs at Shakespear have been through the Kiwi Aversion Programme which sees small shocks given to dogs in the presence of kiwi (dead ones) and droppings.

With Defence Force land, WaterCare and the YMCA Shakespear Lodge also behind the predator fence there has been some extra safety fencing to keep the kiwi safe, including around gun emplacements so kiwi can't fall in, and to keep them away from the predator fence ends which they could get around. Specialist dogs and handlers will also be used to find the kiwi once they have been released.

Just 45 minutes north of the CBD around 550,000 visitors to Shakespear Regional Park each year.

"This is an exciting opportunity for Aucklanders to see these birds," Auckland Council Senior Ranger Open Sanctuaries Matt Maitland says.

Ten birds each from Tiritiri Matangi and from Kapiti have been released.

"Another 20 will be released next year. All adults, the birds will lay one to two eggs a year. The park should eventually be able to support around 100 kiwi."

As with all small surviving populations of species, managing the genetics is important. Breeding with a couple of D'Urville Island birds helped add some genetic variation early on but there are still risks limited variation means the entire kiwi population could be susceptible to the same diseases.

"A Shakespear Open Sanctuary population helps secure the future of this species. It will help us build a larger, more genetically robust population of our smallest kiwi," Kiwis for kiwi director Michelle Impey said. The national charity is funding the capture and release alongside Foundation North and contributions from other organisations and members of the public.

"Creating a new population of little spotted kiwi at Shakespear Open Sanctuary ... will help us build a larger, more genetically robust population of our smallest kiwi," says Michelle Impey.

Though brown kiwi and little spotted kiwi would have shared territory in the wild there are no plans to bring brown kiwi into Shakespear.

"Spotted kiwi are rarer and brown kiwi don't need the high protection of the predator free fence," he says.

"It's great that Auckland can play a significant part in protecting kiwi numbers in New Zealand. This release follows on from the successful return of the North Island brown kiwi to the Hunua Ranges last month after 50 years," Auckland Mayor Phil Goff said.