We’re worried about mohua

Here’s how things are looking right now for mohua/yellowhead; and why conservation will continue to require a lot of ingenuity and quick thinking, in advance of meeting our Predator Free 2050 goal.

Which makes for some weird and wonderful work stories …

By the Department of Conservation

We’re worried about mohua—not just mohua, but definitely mohua—as these tiny kowhai/yellow creatures are currently embroiled in a battle for survival they’re too small, too bright, too loud and too smelly to win on their own.

(More on smells soon).

For a long time we’ve been working to protect the mohua population from predators by means of moving birds to create new colonies, and doing extensive predator control at the most important sites on the mainland.

Recently, we had our Predator Free Manager Brent Beaven on the DOC Sounds of Science podcast to talk about our goal of ridding Aotearoa of rats, stoats and possums by 2050.

Brent has several decades of hands-on conservation experience.

And sometimes feet on, too.

We’ll let him explain that.

Transcript of the above clip:

To get to the point where mohua need to be in Brent’s socks to be safe is …. alarming.

But it is at that stage.

New Zealand has one of the worst extinction records of any nation and, today, some 4,000 native species are considered to be at some kind of risk. Around a quarter of those are in real danger of extinction. Mohua are in this mix.

Mohua were once widespread across the whole of the South Island, but have been radically reduced to a few fragmented and sparse populations since humans arrived — and even these are still declining.

Overall, the mohua population (currently estimated at 5000-20,000) has declined on the mainland in the last 150 years and there are concerns this trend will continue without further intervention.

The evolution

As most Conservation Blog readers will know, native species in Aotearoa evolved in the absence of most mammals. The only mammals that are from here are seals, sea lions, and bats, none of which present a problem to our endemic bird populations.

When predators like rats, stoats and possums were introduced, our problems began.

Mammalian predators like these ones hunt by tīare/scent, sound and sight. They sniff out and track down the things they want to eat. Like mohua, hence we opened this blog by calling them loud and smelly. It wasn’t to be mean, more to point out the odds are stacked against them.

Most stoat predation occurs when the chicks are large and vocal: a stoat can hear them begging for miles around a nest, which acts as a large summoning bell for predators.

(Interestingly, mohua don’t smell quite as distinctive as kākāpō, who are known for their particularly floral pong. The distinct scent of kākāpō birds and nests has been likened to potpourri, or the inside of a violin case, or a bunch of very strong roses).

For both kākāpō and mohua, their habits make them easy pickings—kākāpō nest on the ground, and mohua nest and roost each night in tree holes.

Our birds, having evolved without land-based mammalian predators, were used to looking out and up for ruru and Haast’s eagle and the like. Their defence was to stay still and quiet and wait for the predator to keep flying.

It’s also why our native species are fauna coloured – no neon parakeet pinks or mcaw reds for our birds. We stick to the blues of water, the yellows of flowers and greens of the ngahere.

Our birds need to blend.

But blending is no good when you smell, and when you’re loud, and you nest in very easy-to-reach places.

We’ve lost too many of our native species in the last 800 years.

So we’re in a bind.

A big, bird bind.

We could do a deep dive on all of our Threatened and At Risk species, but today it’s mohua.

How are mohua doing, you ask? Not great

Mohua are a taonga for Ngāi Tahu. They’re sparrow-sized, yellow-headed birds found only in the South Island in native forest.

Mohua were once widespread, found all over the beech forests of the South Island. But by the mid-1990s the population was in Very Serious Trouble. By this time, mohua had disappeared from more than 90% of the South Island. In places like the Landsborough Valley, there were just over a dozen left.

Mohua were looking extinction in the face.

Through intensive predator control, the decline in the Landsborough Valley was reversed.

But we’re a long way from home safe for mohua.

Our predator control has not been intensive enough at most of the other core sites.

Because mohua are extremely sensitive to predators, they’re often an indicator species for how successful predator control is in an area. If you see lots of mohua, things are going great.

But we’re not seeing that in many places.

Mohua are responding well to predator control in the Landsborough in South Westland and Hurunui South Branch in Canterbury, but are currently declining at other key sites such as the Catlins, Blue Mountains and Dart and Eglinton valleys.

We know for a fact that aerial 1080 saves species, and we wouldn’t have a hope of keeping anything alive without it. We’re on the lookout for a better tool, but until then, 1080 is the only large-scale option we have.

For mohua, just like all endangered native species, the period between mast and 1080 application is critical and requires extensive complementary trapping networks to keep stoat numbers down.

Let’s walk through this:

In Landsborough and Hurunui South Branch, where there’s 1080 use as well as extensive trapping networks to keep predator number under control in between mast times, mohua are having a ball*

(*Well, close. They’re slowly increasing, but compared to rapidly decreasing, that’s a ball).

However, at sites such as the Catlins, Blue Mountains and Dart and Eglinton valleys, they’re still declining. The reasons behind this are complex but it’s to do with masts.

A mast is when more flowering trees leads to more seed, leads to more predators, leads to more predation. (Here’s an animated short showing how this works). It doesn’t happen every year, but when it does, there’s an explosion in predator numbers.

There are a few reasons for mohua to be struggling in some sites, despite our best efforts.

Monitoring shows that using aerial 1080 to control beech mast predator plagues is more effective in silver beech forest than in red beech, which produces more seed.

And predator control regimes relying on aerial 1080 without extensive complementary trapping networks to keep stoats down between forest masts also seem less effective for mohua.

Climate change plays a factor too, as the increasing frequency in forest masts means species like mohua have less time to recover between masts, because more rats naturally survive the winter.

The Mohua Recovery Group, which includes Department of Conservation and Ngāi Tahu representatives, is looking at options to improve management at these sites to try and turn this trend around.

And it’s fair to say that conservationists and Predator Free experts, like Brent, are busting a gut trying to do their best for mohua.

There are also mohua populations which appear to be stable on the eight pest-free offshore islands in Fiordland and Southland, where additional populations (estimated at 3000 birds) have been successfully established.

But these populations are reliant on everybody undertaking good island biosecurity. Pest incursions to these islands would be costly and deadly for precious species.

This is all to say: mohua aren’t yet in the green, despite improvement at some sites.

So what?

This is why Brent’s story about catching mohua in his socks was a laugh-then cry moment.

One of those ‘oof that’s funny but dire’ situations.

Someone catching birds in their socks and popping them in pockets is funny.

The fact they’re doing it because the species is in dire straits and will die out unless we can get enough birds to translocate them to offshore islands, which is currently the only way we can be confident about their survival is not so funny.

Brent told us the mohua-sock story recently and we published it on the podcast last week, but the actual sock-catching happened years ago. This was on Breaksea Island to get enough birds to successfully establish a population on Whenua Hou.

It worked.

Brent’s socks weren’t an elegant solution, but they were a solution. 

The mohua population on Whenua Hou is doing pretty well, because it’s a predator free island.

If we can meet our ambitious goal of making all of Aotearoa Predator Free by 2050, our mohua could become a frequent sight on our main islands.

Imagine mohua all around Te Waipounamu/the South Island!

That would be neat.

To hear Brent explain the PF2050 goal and lay out the key mahi, have a listen to the DOC Sounds of Science Podcast, available wherever you get your podcasts. Part 2 of our chat with Brent will be out next week.

Episode 13: Predator Free and me (part one) – DOC Sounds of Science Podcast

Brent Beaven tells us everything we need to know about New Zealand's goal to be Predator Free by 2050. How will we? What is this? Is it even possible? Brent has the answers. In fact he has so many, we’ve split his interview in two. Brent is an expert on predator control and has decades of hands-on field experience. He's herded sea lions, been hounded by kiwi, and caught mohua in his socks. In the world of threatened species conservation, you name it and Brent has done it. Listen and learn. Show notes available at http://www.doc.govt.nz/podcast

For more about mohua see: https://www.doc.govt.nz/get-involved/run-a-project/translocation/translocation-success/mohua/