A rare New Zealand bird has been evacuated to a remote island despite the strict coronavirus lockdown, with the high-risk mission “essential” to the survival of the species, conservationists say.

Despite stringent lockdown orders in place country-wide, as New Zealand battles Covid-19, five juvenile shore plovers – or tūturuatu – were flown from captivity in Christchurch to the remote, predator-free Mana Island off the coast of Wellington on Saturday.

The birds caught a near-empty Air New Zealand flight for the 450km journey, taking up full rows, and being monitored by cabin crew who have few human passengers to attend anymore.

Conservation minister Eugenie Sage said a lot of careful planning went into staging the operation.

“There are just 250 of these birds left in the world and these juveniles are a critical part of attempts to establish a self-sustaining population on the pest-free Mana Island so numbers can grow,” Sage said.

The journey of the critically threatened species – whose juveniles become violent if quarantined in small spaces for too long – was deemed “essential”, and stringent planning went into place to keep the birds and their human carers safe throughout the journey.

There are only 250 tūturuatu left in the country, with the population vulnerable to attack by predators such as rats, stoats and cats.

Dave Houston at the Department of Conservation (DoC) said the birds were part of a third transfer this year that was put on hold when New Zealand went to alert level four.

“A review highlighted the serious welfare risks posed to the birds by further delays. The young tūturuatu have been … in a small quarantine aviary and, like us, are subject to stress when confined, but with more serious health implications,” he said.

Death by territorial aggression or stress-related health problems were a very real possibility if the birds were not relocated immediately, said Anne Richardson, wildlife manager at the Isaac Conservation and Wildlife Trust, and the loss would have been a real blow after a successful breeding season.

Strict Covid-19 lockdown regulations are in place country-wide, banning any non-essential domestic travel and international travel.

Nick Fisentzidis and son Theo check on a New Zealand shore plover during their transfer to the predator-free island of Mana Photograph: Department of Conservation, New Zealand

A sole carer travelled with the shore plovers for each leg of the journey, and social distancing measures were carefully maintained at pick-up and drop-off points, as well as extensive use of PPE. The urgent relocation was personally approved by the conservation minister.

“Getting the birds to Mana Island as soon as possible is the best outcome,” said Houston.

Now the birds have arrived, they have a strong chance of survival

“Released juveniles are more likely to view the release site as their new home when they are in larger numbers,” Houston said. “The birds help to anchor each other to their release site. Establishing new populations is critical to the recovery programme and we cannot afford to lose one year’s worth of effort.”

DoC ranger Nick Fisentzidis has remained as caretaker and manager on Mana Island with his family, and they are all self-isolating together, as well as caring for the local animals.

The plover will be fed by Fisentzidis to help acclimatise them to their new home, before being released in a few days.

There have been more than 1,200 cases of coronavirus in New Zealand and five deaths. A total lockdown of the country was implemented on 25 March, which has stopped the DoC doing the majority of its work, including pest control. Only the most at-risk and endangered animals kept in captivity or breedings centres continue to receive care from DoC rangers during lockdown.

The prime minister, Jacinda Ardern, will make a decision on how long the country’s lockdown will continue next week.