One kokako doesn’t make a summer

In the world of applied conservation even the successes can be failures. Almost a decade ago the New Zealand government committed to eradicating pests (stoats and red deer) of Secretary and Resolution Islands, two huge in-shore islands, nearly 30,000ha of remote and mostly extreme forested terrain.

Secretary Island

The steep forest slopes of Secretary Island, Fiodland National Park. photo: James T. Reardon)

This grand effort to rid these islands of their invasive pest species was not made on a whim (although the political back-story makes interesting telling); conservationists saw the potential of these islands to hold robust and ecologically meaningful populations of species now extinct on the mainland. Those conservationists weren’t just the late 20th century types either. Back in the 19th century Mr. Richard Henry, an Irishman, via Australia, saw both the wonder and beauty of New Zealands strange endemic biota and also the potential roles that the large islands like Resolution might play in cheating their extinction. Henry had witnessed the release of mustelids into NZ at the behest of the pastoral lobby to control rabbits, and within a decade of the event had observed the steady eradication of species such as kakapo and whio (blue duck) as the introduced predators swept across the mainland. Diligently, he set about translocating kiwi and kakapo onto Resolution Island in the belief that the introduced predators sweeping the mainland would be held at bay by the ocean current. Sadly, in the early 1900s stoats arrived on Resolution Island and Henry called it quits. One can only imagine the depression such a realisation would bring after many years of remote hardship apparently all for nothing.

Richard Henry outside his boatshed, Pigeon Island, Dusky Sound, Fiordland, March 1900

Richard Henry outside his boatshed, Pigeon Island, Dusky Sound, Fiordland, March 1900. image: Te Papa

Over 100 years later and the eradications are well under way, but the same cause of Henry’s abandonment, the stoats ability to swim amazing distances in rough cold oceans, still plagues progress. Despite extensive trapping that is serviced 4 times a year, new immigrant stoats still arrive. Sometimes there may be a lull, sometimes a spike, but rarely a year goes by that individuals to dozens of stoats are not being removed from the island.

With such small numbers of stoats left on the islands it’s easy to see why conservationists want to start releasing threatened species as even the most sensitive could possibly recover if predation is kept to a minimum and only a small handful of predators roam the vast islands. So it was that in 2008 and 2009 that kokako, 26 in all were released onto Secretary Island. It was the first wave of species reintroductions and special in itself as North Island kokako, which were to be used for the release were ecological surrogates for the now extinct South Island kokako. Whilst sightings were not common, in early 2011 what we all hoped was a sure sign of success, the first Secretary Island fledged bird was observed. Wattles still a glorious mauve, the bird came to our recorded calls and hopped around us for over half an hour.

kokako juvenile, Secretary Island (photo: James T. Reardon)

The first and only known kokako to be fledged on Secretary in recent times (photo: James T. Reardon)

We were ecstatic. My partner especially as she had fund-raised and managed the complex politics and logistics of getting these birds from their North Island forest homes, safely down to Fiordland. That very afternoon it was resolved: we needed to thoroughly survey the whole island to understand the full extent of successful establishment before supplementing the population with a further translocation to ensure a genetically robust founder population.

Juvenile kokako  (Callaeas cinereus) inspects the conservationists (photo: James T. Reardon)

Juvenile kokako (Callaeas cinereus) inspects the conservationists. photo: James T. Reardon

Fast-forward to March 2013 and the survey is underway, with 8 kokako experts and tough conservationists ready to spend a week with gps and call recorders scouring the islands suitable habitat to take a census of the kokako. The weather, in a very un-Fiordland like manner turned to clear blue skies and virtually no wind for the whole week. The on-going deer and stoat eradication gave the team amazing access to helicopter and boat transport. Perfect except that in a long week of searching absolutely no sign of kokako was recorded. Not a single note heard. As if that was bad enough, South Island robin, released onto the island the same year (2008) were nowhere to be seen either. The team also noticed that the introduced blackbird was significantly less abundant than in previous yrs. A look at the data when back in the office confirms this. The robins are as much of a mystery as the kokako. For 2-3 years they seemed to be doing well, spreading across the island and breeding. Other bird species seem to be on the mend, bell bird and weka numbers have certainly recovered post 2006.

This is bad news. Conservation dollars are very hard to come by, we don’t waste them. To not waste the time, money and effort expended to put kokako on Secretary Island we need to understand why it failed. The habitat seems good, and was proven good enough for a least one pair to raise a chick to fledging. Predator numbers are extremely low but there are in addition to stoats, both falcon and weka on the island. But in their North island strongholds kokako recover in the presence of both falcon and stoats probably at higher abundances than on Secretary. Secretary island is free of rodents and possum, so could it be some strange predator-prey relationship? But then it’s hard to imagine that stoats would kill more than the incubating females and maybe naive fledglings. Weka surely couldn’t eradicate a bird with limited but perfectly functional abilities of flight? What about climate? Well whilst these islands are hundreds of kilometers south of their original home, the climate of these islands is ameliorated by the oceans that surround them. Disease? This is certainly a possibility. During their translocation health screening detected haemogregarine parasites that were previously unknown to science. These hypotheses need data and those data aren’t cheap. But conservation is a science, all be it a very practical science where many of the best practitioners are pragmatists and ‘get it done’ types.

Before we charge into fund-raising to answer these questions there is one other species to check up on. Rock wren, New Zealand’s only true alpine bird and a member of the once numerous (and largely flightless) Xenicus genera that are basal to all modern passerines. This species is vulnerable to nest predation by both rodents and stoats and in an effort to offer them some security a founder population was released onto Secretary Island in 2009-2010. We know they bred initially but what of their fate three yrs on. Time to go and check.

female rock wren, Xenicus gilviventris, New Zealands only true alpine bird and vulnerable to the ravages of both stoats and rodents (including mice) in it's remote alpine home. (photo: James T. Reardon)

Female rock wren, Xenicus gilviventris, New Zealands only true alpine bird and vulnerable to the ravages of both stoats and rodents (including mice) in it’s remote alpine home. photo: James T. Reardon

~ by motolorax on March 17, 2013.

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