Staring down the barrel of an ecological disaster, conservationists were left to hedge their bets when it came to saving a critical population of one of New Zealand's most endangered bird species.

It was October 2011, when the grounding of the containership MV Rena off the coast of Tauranga was poised to swamp Bay of Plenty beaches with hundreds of tonnes of spilt heavy fuel oil.

As conservationists scrambled to rescue other birds, including hundreds of little blue penguins from around the shores of Tauranga, ecologist Dr John Dowding helped make the call on what to do with 120 NZ dotterel spread across about 70km of coastline.

Although dotterels had been raised in captivity, never once had the species been recovered and taken out of the wild.

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"There was still 1300 tonnes of oil on the Rena and she'd already leaked 350 tonnes and they hadn't yet stopped the flow, so we thought, hell, there's a lot of oil still out there and we are going to lose an awful lot of birds," said Dr Dowding, who revealed new insights into the rescue at the New Zealand Ecological Society's conference in Christchurch today.

"So we thought we'd hedge our bets and take 60 into captivity, which would provide an insurance population if the other 60 that were left out there got killed by oil.

"On the other hand, if everything turned to custard with our captive situation, and we lost a lot of birds from having them there, we'd still have half the birds out there in the wild, taking their chances with the oil, and we'd always have the chance to catch any that got oiled and rehabilitate them."

While some of the captive dotterels died from a disease - the result of stress from being held in captivity for weeks - the majority survived and were able to be returned to breeding beaches that had been cleaned while they were gone.

The majority of the captive dotterels survived and were able to be returned to breeding beaches that had been cleaned while they were gone. Photo / Supplied
The majority of the captive dotterels survived and were able to be returned to breeding beaches that had been cleaned while they were gone. Photo / Supplied

Dr Dowding's follow-up monitoring showed that, while population numbers took a slight dip after the first year, by the second, three-quarters were still at the sites they'd been caught at.

"So essentially, it looked very much like, after two years, it was business as usual again for dotterels in the Bay of Plenty."

The major lesson had been that the birds were able to be recovered and taken into captivity, although some elements of their handling would need to be improved in the next operation.

"The other really big lesson was the timing," he said.

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"Now, we've got enough information that, in the event of this happening again, we'd be able to go to the authorities and say they've got to clean up the beaches within five weeks - otherwise birds will start dying in captivity."

Meanwhile, researchers from members of Massey University's Wildbase Oil Response Team have shown oiled birds that are rehabilitated are also able to return to normal behaviours after an oil spill.

They say these findings justified the costs of oiled wildlife response worldwide.
After the Rena spill, 383 Little Blue penguins were captured, cleaned, cared for and released back into a cleaned environment.

Previous research had shown these rehabilitated penguins to have similar survival rates to other, unaffected birds in the area.

In a new study, published in the Marine Pollution Bulletin, scientists evaluated the foraging (diving) behaviour of eight rehabilitated birds using tracking devices and compared it to the behaviour of six unaffected birds.

A group of little blue penguins at the Oiled Wildlife Response Centre that was set-up during the grounding of the MV Rena in 2011. Photo / Alan Gibson
A group of little blue penguins at the Oiled Wildlife Response Centre that was set-up during the grounding of the MV Rena in 2011. Photo / Alan Gibson

They found both rehabilitated and non-rehabilitated birds were behaving similarly - diving to similar depths and in similar locations.

By analysing the carbon and nitrogen levels in the birds' feathers, they were also able to show the penguins were feeding on similar prey.

Co-author on the paper, Dr Louise Chilvers from Massey's Institute of Veterinary, Animal and Biomedical Sciences, said it was also necessary to evaluate the behaviour of animals affected by oil spills, not just the overall survival rates.

"Oil pollution not only affects the larger animals, like the little blue penguins, but can have severe impacts on all levels of the food chain, from krill all the way through to fish. Obviously, an animal's ability to forage affects their long-term survival."

This study, along with other research done over the last two years, indicated the birds were finding and eating enough prey to gain the nutrients and energy they need to survive and reproduce at similar rates to other populations of little blue penguins in Australia and New Zealand.

Dr Chilvers said the study justified the need to continue supporting oiled wildlife response.

"Opponents of oiled wildlife response argue that rehabilitation is an expensive anthropogenic need to lessen the stress of oiled wildlife and has very little or no conservation value.

"This research shows rehabilitation and intervention is effective both in the short and long term."