How Christchurch lost its tūī, and how to bring them back

Wednesday, 25 August 2021

Early settlers stripped Christchurch of its bush, taking many species with it. Ecologists now say a change of perspective could bring them back. AMBER ALLOTT​ reports.

Nature-loving Kiwis have long lamented the disappearing dawn chorus as native bird species decline across New Zealand.

But one pair of ecologists say the key to bringing it back to our cities could be a shift in how we think about our own backyards.

Stuff and The Press are trying to help Christchurch become New Zealand’s first National Park City – a greener, healthier, and wilder place to live.

It is a large-scale and long-term vision that will give relationships between people and nature a pivotal role in the city’s planning and decision-making.

**READ MORE:

* Bird counts: Important for conservation, and not always a walk in the park

* 'Tūī Corridor' planned to bring the native bird back to Christchurch

* Signs the elusive tūī may slowly be returning to Canterbury

**

Christchurch, and the broader Canterbury Plains, have had vast swathes of native bush cleared for productive farmland since they were first settled. Research from 2004 found the plains had less than 0.5 per cent of its native plant cover left.

As a result, Christchurch is the only major city without tūī, one of the country’s most beloved songbirds.

Ecologist Laura Molles, an expert in animal behaviour and conservation, says tūī disappeared gradually from the region, with Banks Peninsula their last stronghold.

“They disappeared almost entirely around 1990. Their numbers had been declining for many decades, but by that point, there wasn’t a breeding population left any more.

“There’s never really one thing that causes a species to go extinct, there’s a whole combination of factors. The one thing they have in common is that they’re all our fault.”

For tūī on the peninsula, habitat loss played a big part.

By about 1900, Banks Peninsula forest coverage got down to a low of about 1 per cent, leaving no food, and no place for the birds to live, Molles says.

At the same time, mammalian pests were being introduced, and their populations started to climb rapidly.

“These are a huge threat to tūī and other bird species. Tūī are a species we know responds really well to predator control.

“Browsing mammals as well, so deer, pigs, goats, stock getting in forest areas would have degraded what habitat was left too, their food supplies.”

As the population dwindles they become more vulnerable to chance, and a storm near one patch of forest could mean no breeding happens that year, Molles says.

“A lot of species didn’t make it… Tūī were one that actually managed to hold on for a lot longer than the other species.

“The ones that we still have here, the korimako, the grey warbler, the fantail, they have actually been able to pull right through, and in some cases they’re now increasing because of positive work people are now doing to try and protect them.”

In 2009 and 2010, Molles helped reintroduce more than 70 tūī to Banks Peninsula, and close to 20 per cent of the area is now covered in regenerating forest.

“At the point we were doing this, tūī had never been reintroduced anywhere before. We didn’t really know what to expect, if it would work.

“Translocations of bellbirds have been attempted – they’re probably the closest species – but they haven’t gone very well. They had to move a lot of bellbirds to get any to stick in Wellington.”

But the tūī is a success story. After months spent gorging themselves on kahikatea fruit in Hinewai Reserve, where they were first released, the population moved on and based itself around Akaroa.

But while tūī can and do visit parts of Christchurch during their winter hunt for food, Molles says if people want them year-round, they need to create a home for birds in suburbia.

“Crossing 7 kilometres of pasture, no problem. It’s nothing to them … but during the breeding season, they need all of their resources to be in one place, and this is especially true for a female bird who needs to sit on a nest, and feed her chicks.”

A mother bird needs to dart off the nest maybe once an hour, she says.

“When she’s feeding her chicks, she needs to find all these insects [for them], and to keep herself fuelled up with fruit and nectar. For tūī, they need to be able to do all of that within a few hundred metres of where they’re nesting.”

Each pair needs one or two hectares of continuous forest to make it through the breeding season. Even places like Riccarton Bush or the Botanic Gardens could only ever support a few pairs of bellbirds, and even less of the larger tūī.

A lack of food isn’t the only threat intrepid, urban-dwelling birds face. Pests including rats, stoats, ferrets and possums are a major danger in the city.

“But then we have our pets. Cats are a big problem, potentially, if we want to have native birds nesting in the city.”

Buildings also pose a risk, as well as cars, she says.

In the Akaroa tūī population, causes of death were known for about 35 birds.

“Half those are birds hitting windows or glass balustrades. We have another five that were hit by cars, and two cat predations.

“Most of the deaths that we know about have been things that are really particular to suburban environments, so that’s something else we’re going to need to think about if we want to encourage birds in our cities to stay there and live year round.”

Molles’ husband, Lincoln University senior ecology lecturer Jon Sullivan, says there needs to be a shift in how people see their parks and gardens.

In terms of planting, that meant letting things get a little messy.

“Less tidy – nature doesn’t want it to be super tidy.”

On his runs and bike rides around the city, about 90 per cent of the pīwakawaka (fantails), riroriro (grey warblers) and korimako (bellbirds) he sees are in the few patches of dense vegetation that have cropped up, often the result of community planting projects, Sullivan says.

“[We need] more dense, protected forest where these birds can hide from predators, which we don’t tend to have – we tend to have oak trees and daffodils and lawn.

“If you’re going to roost, or you’re going to nest, you want somewhere safe to do it that’s not going to be found by a rat. You want to be in a big, complicated thing, not just in a nice, standard, trimmed tree. The rat’s going to find you up there.”

Molles says tūī love nesting in places like the tangly tops of kānuka, a plant that once thrived in Canterbury’s dryland ecosystem.

“You want things that are complex and messy because that’s where all the invertebrates live. We want native invertebrates in the city as well, not just because they’re amazing, but also because they’re food for birds.

“It’s one of those other things a lot of native species need, specifically to feed their chicks. If that complexity is not there, it makes it that much harder for them to make a living in the city.”

Anyone with a backyard could help, so long as they are willing to lay off the manicuring.

“Especially if you have a whole neighbourhood that starts moving in that direction, suddenly you’re getting to the point where you have enough habitat for some birds to start nesting.”

However, how and what we plant is just one aspect, and some tough conversations need to be had to stop the city being a “death trap” for wildlife, Sullivan says.

“We also need to think about, do we need to have such a high density of cats, do they need to be outside, free-roaming all the time?

“That’s a conversation we still need to keep having. Do we want birds or cats? There’s a balance we need to come up with here as a society.”

There are also options available to help stop birds from banging into windows, he says.

“Overseas you can get glass with UV markings imprinted in it the birds can see, but we don’t tend to have that in New Zealand.

“All the solutions are there, it’s just a matter of putting them all together.”

The pair both support the National Park City initiative.

Sullivan says there are great things in the city that need to be both celebrated and protected.

“There are as many native species in the wider Christchurch area as there would be in one of our national parks, [but] they’re not abundant.

“They’re all on the fringes in these little patches of vegetation here and there, often struggling. They need to be higher profile, they need to be looked after better.

“Having Christchurch as New Zealand’s first National Park City – if we got there first – would be a fantastic way of saying that we care about these things, and we are going to think about how to build a city that treasures all of our inhabitants, and allows what was here before we arrived to thrive around us.”

Eco-sanctuary could have dramatic impact on birdlife

Christchurch is the country’s only major centre without a large, predator free eco-sanctuary, but a local charitable trust is working to change that.

Waitākiri Eco-Sanctuary Trust chair Bruce White says their proposed 180-hectare sanctuary, in the heart of the Christchurch red zone, will be a perfect fit for the National Park City concept.

“I see the red zone as a wonderful opportunity for Christchurch.”

The trust’s proposal, which it is trying to get the Christchurch City Council on board with, involves fully fencing 50ha of red-zoned land in east Burwood, and combining it with Travis Wetland.

“One of the most unique aspects, unlike Orokonui in Dunedin for example, is it’s surrounded by suburban land, rather than being in a rural environment.

“A lot of local people will be wanting to visit, so it’ll be designed to be completely accessible to the public.”

Travis Wetland is already regarded as ecologically significant, and White says the eco-sanctuary could have a dramatic effect on the city’s biodiversity.

“Like Orokonui and Zealandia, it provides a habitat for the regeneration of species, who then move out into other parts of the city.

“It’s called the ‘halo effect,’ [and] it’ll help the regeneration go much faster without predators.”

Birds like tūī, kererū, and South Island kākā travel as far as 15km for food, while kākāriki, whio (blue ducks) and native bats will travel up to 5km.

Having Waitākiri as a safe stronghold means people across the city could soon have a rainbow of rare natives gracing their gardens.

“The Avon Corridor could be absolutely wonderful … [but] collaboration with council is vital.

“Christchurch has tremendous potential – the sooner we get on with it, the better.”