What makes a city 'walkable'?

Te Herenga Waka—Victoria University of Wellington PhD student Swarnali Dihingia’s research is at the crux of New Zealand’s intensification debate.

Swarnali stands on Cuba street with her arms crossed.

The National Policy Statement on Urban Development 2020 (NPS-UD) requires a six-storey minimum building height within the walkable catchment of rapid transit stops or the edge of the city centre and metropolitan centre zones.

Now, cities and communities that are for and against intensification—that is, creating urban living spaces that are much closer together than the currently more common sprawl of cities—are debating what is ‘walkable’. Swarnali’s research aims to help answer this question, using tourists as an indicator of how walkable a city is.

“Tourists are more susceptible to the qualities of the urban environment, its safety, and the level of comfort and pleasantness a city has to offer,” Swarnali says. “These elements play a significant role in determining whether a route is suitably walkable or not."

To learn more about the walkability of our cities, Swarnali has investigated tourists’ walking routes and behaviour in Wellington and Christchurch and how they interact with the city topography, public life and spaces, and weather conditions (including Wellington’s often challenging wind).

“New Zealand cities are a blend of high-quality urban spaces that cater for pedestrians, such as Wellington’s Cuba Street or Christchurch’s new downtown areas. However, the underinvestment in public spaces outside these locations has a clear impact on walkability”, she says.

Swarnali’s initial findings have shown that while many central environments in Wellington and Christchurch are accessible to pedestrians, the streetscape elements did have a significant impact on pedestrian comfort and satisfaction with the route. In particular, the tourists felt unsafe on the pedestrianised Wellington waterfront due to distress from running into cyclists and scooters or from overcrowding.

Swarnali encourages local authorities such as Wellington City Council and Christchurch Council to consider tourists as a metric for understanding walkability and walking behaviour as they are the most susceptible to what the city has provided.

“There is much more at stake here than a walkable commute. Walking routes are also economically profitable to businesses and have positive physical and mental health outcomes.”

To advance her research, Swarnali is seeking engagement with Wellington City Council and Christchurch City Council, Waka Kotahi, the tourism sector, walking advocates, and individuals. From engaging these organisations and people, she will provide insights into where and how to improve walkability in New Zealand’s cities. With discussions unfolding across New Zealand due to the National Policy Statement on Urban Development and the Resource Management Act reforms, these insights will be critical in defining walkable catchments for urban intensification.

Swarnali Dihingia is a PhD candidate in the Wellington Faculty of Architecture and Design Innovation under the supervision of Associate Professor Morten Gjerde and Professor Brenda Vale.

Contact Swarnali to hear more about this research on swarnali.dihingia@vuw.ac.nz.

Kei hea te Kererū?

Through interactive maps of the Great Kererū Count, student Samuel Rammell is mapping the way to future ecological restoration through citizen science.

Kereru counts maps comparing 2014 data to 2020 data
Kererū count observation maps created by Samuel Rammell.

Rammell, a Master of Science student at Te Herenga Waka—Victoria University of Wellington, is putting his vision for environmental conservation into action by taking on a pivotal role for the Great Kererū Count.

“The environment has been degraded so much, in so many different ways, that conserving or preserving what we have left, while extremely important, is not enough. We need to actively restore the environment around us,” he says.

The Count—the final of which was held in September this year—is a national survey that relies on citizen scientist data collection to measure the abundance, distribution, and behaviour of Aotearoa’s endemic pigeon. It is, as Rammell calls it, “a real passion project.”

Building on the past eight years of data, Rammell has produced interactive maps of Aotearoa which display the 2021 observations.

“This project focuses on presenting some results from this year’s count back to the people who made it possible, the citizens.”

Rammell is eager to analyse the project further within his thesis, which is set to explore how best to use the data collected.

“Hopefully, this will provide us an updated look at kererū populations throughout New Zealand as well as a new method for analysing citizen science data."

“Citizen science allows collaboration between the public and scientists. This gives scientists access to large data sets, some of which can reveal trends that institutional science can't, while providing citizens with the opportunity to engage in meaningful scientific research, learn, and, in the case of The Great Kererū Count, build their connection with nature.”

The interactive map for 2021, along with a full break down on what the observations mean for kererū, can be found on Rammell’s Great Kererū Count webpage.

Written by Master of Science and Society student Poppy McGuigan-Hay.

Tuatara’s speedy sperm may provide conservation clue, say study authors

PhD candidate Sarah Lamar has discovered that tuatara sperm are the speediest so far discovered in the reptile world.

Published 4 August 2021


Tuatara, Aotearoa New Zealand’s surviving remnant from the age of dinosaurs, are not noted for their speed. But new Te Herenga Waka—Victoria University of Wellington-led research has turned up one surprisingly swift aspect of their anatomy—their sperm.

“While this is a pilot project and more work is ongoing, initial results indicate tuatara sperm may be the fastest reptile sperm ever analysed—two to four times faster than any previously studied reptile,” says Sarah Lamar, a PhD candidate in the University’s Te Tumu Whakaoho Mauri o te Ao Koiora—Centre for Biodiversity and Restoration Ecology (CBRE) and lead author of a PLOS One journal article about the findings.

Despite massive conservation efforts, much about tuatara reproduction remains unknown,

“Our pilot project was the first time we had had live, mature sperm from a tuatara,” says Ms Lamar. “There has been a huge focus on their conservation, but large gaps in our knowledge of male reproduction remain, which is rather surprising.”

Gathering the sperm was the initial challenge. Unlike other reptiles, male tuatara do not have a penis. Instead they mate in a similar way to birds, by lining up their cloaca with that of the female.

“Tuatara are the only living reptiles to mate in this way,” says Ms Lamar. “We conjectured that the speed of the sperm may be because it has a limited time outside the reproductive tract before it becomes non motile (or stops moving), so the faster they can get into the cloaca and female reproductive tract, the more likely they are to be successful at fertilising the egg.”

The researchers found the best way of getting a sample was to wait until the tuatara were actually mating. Although this meant breaking up mating pairs of the reptiles, they do mate multiple times within a season. “It took luck and chance and being at the right place at the right time,” says Ms Lamar. “You can miss it easily but the actual samples are concentrated—a tiny drop has millions of cells.”

Tuatara today occupy less than 10 percent of their historic range. The sex of tuatara hatchlings depends on the temperatures they are exposed to, with more males hatching at warmer temperatures. Projected temperature rises because of climate change are likely to mean many more males being born, and skewed sex ratios in the population can lead to eventual extinction.

“Developing breeding programmes by storing tuatara eggs and sperm cryogenically is a form of insurance,” says Ms Lamar. “We want to develop methods of cryopreservation ahead of time. Storing at extremely low temperatures preserves the integrity of the cells for a significant amount of time—in theory indefinitely—as long as they are stored in the correct chemical.

“Our first study showed quite a bit of variation between individuals and a lot of variation depending on the storage treatment. We are looking at finding the right combination of chemicals that retain cell integrity, with no ice damage, and the correct freezing regime.”

During a recent field season, the team took more samples.

“Using the chemicals that we found worked in the pilot study, and some new chemicals that work in a similar way, we will continue to investigate the best cryopreservative for storing tuatara sperm,” says Ms Lamar.

“We are also looking at more samples to confirm the sperm motility rates and to investigate whether motility relates to the physical aspects of a good male. We have found in other studies that larger males are more successful in fighting off others and being chosen by females. We are yet to find if that is related to sperm motility, and are working on that now.”

Ms Lamar’s fellow researchers included colleagues from the CBRE, which is part of the University’s Te Kura Mātauranga Koiora—School of Biological Sciences, and collaborators at the University of Otago and Grand Valley State University in the United States.

She and they have written an article about the project for The Conversation and it is available for free republication under Creative Commons.

Citizen scientists add to understanding of harmful monarch butterfly parasite

Thanks to nearly 100 volunteers, University entomologists are rethinking how Ophryocystis elektroscirrha and wing deformity are connected.

Published 9 July 2021


Te Herenga Waka—Victoria University of Wellington researchers have thanked the nearly 100 volunteer citizen scientists around Aotearoa New Zealand who provided samples from monarch butterflies to help determine how many of the popular insects have been harmed by a potentially deadly parasite.

The only previous survey for the parasite Ophryocystis elektroscirrha (OE) in New Zealand sampled six butterflies, but the citizen scientists enabled Professor Phil Lester and Dr Mariana Bulgarella from the University’s Te Kura Mātauranga Koiora—School of Biological Sciences to look at more than 550.

As a result, the entomologists are rethinking how OE and wing deformity in the butterflies are connected.

OE can harm monarch butterflies in many ways, including their pre-adult survival, adult body mass, mating ability, fecundity, flight ability, and adult lifespan.

The citizen scientists, ranging in age from 4–86 years, responded during last year’s COVID-19 Alert Level 4 lockdown to a callout in media and elsewhere by Professor Lester and Dr Bulgarella.

Between mid-April and late-July, from Dunedin to Doubtless Bay in Northland, they used clear sticky tape to collect spores from the abdomens of the butterflies—a harmless process when following the researchers’ instructions—and also recorded their physical condition and sex.

Based on the citizen scientists’ contributions, Professor Lester and Dr Bulgarella have now published a research paper in the journal Ecological Entomology.

In it, they outline how they found wing deformities in the butterflies increased with lower temperatures, while the prevalence of OE decreased, with the parasite preferring higher temperatures. No OE were observed in the coldest locatation of Dunedin, but all samples were infected in the warmest one of Doubtless Bay. The prevalence of OE and wing deformities did not vary with the sex of the butterfly.

The researchers had expected wing deformities to increase with parasitism rates, as in international studies, but their findings did not show this.

By way of possible explanation, Professor Lester says, “We believe temperature affects both the parasite and the butterfly independently. Cold temperatures during development cause wing deformities in these butterflies, which is why you see more deformities the further south you go. The parasite also seems unable to tolerate cold conditions. In the warmth of Northland, it is abundant, but environments like Dunedin appear too cold for OE.”

As a result of their findings, Professor Lester and Dr Bulgarella suggest the butterflies may perform better at intermediate temperatures and conservation approaches may therefore need to be tailored regionally.

“These are important findings and they would not have been possible without so many New Zealanders volunteering to help us,” says Professor Lester. “This project emphasises the value of citizen scientists for researchers and we cannot thank those who took part enough. Because of you, we are a step further in our understanding of monarch butterflies and the threat OE poses to them.”

Study shows a short time to save coral reefs

University marine biologist Dr Christopher Cornwall has some good news to offer amid a grim outlook because of the scale of carbon dioxide emissions.

Published 11 May 2021


Image by David Clode on Unsplash.

The window of opportunity to save the world’s coral reefs is still open but time is running out, new research shows.

An international study jointly led by Te Herenga Waka—Victoria University of Wellington marine biologist Dr Christopher Cornwall has calculated how coral reefs are likely to react to ocean acidification and warming under three different climate change carbon dioxide scenarios—low, medium, and worst-case.

The study, just published in the journal PNAS, has some good news to offer amid a grim outlook.

Dr Cornwall, a Rutherford Discovery Fellow in the School of Biological Sciences, who earlier this year won a $200,000 Prime Minister’s MacDiarmid Emerging Scientist Prize, says if the world can reduce carbon dioxide emissions drastically coral reef growth will be reduced “but many reefs will still be able to grow.

“Some of them will even keep pace with sea-level rise. Even if we fail with those reductions but do keep within the intermediate emissions scenario, some coral reefs will still keep growing for a short while, but by the end of the century they will all be eroding.

“If we hit the worst-case scenario, very shortly all coral reefs will be eroding.”

The research by academics in New Zealand, Australia, the United States, France, the Netherlands, and the United Kingdom breaks new ground.

Jointly led by Dr Cornwall and French colleague Dr Steeve Comeau, the interdisciplinary group of scientists initially formed in 2016 as a working group led by the Australian Research Council’s Centre of Excellence for Coral Reef Studies.

Although there has been research investigating the impact of climate change on individual corals and coralline algae, the new study gives broader projections of ocean warming and acidification, and their interaction, on the net carbonate production of coral reefs.

“We have known for more than a decade ocean acidification will affect the ability of calcifying coral reef taxa to form their calcium carbonate skeletons, a process called ‘calcification’,” says Dr Cornwall.

“Also, we have known ocean warming brings increasing frequencies of marine heatwaves that cause coral mass bleaching, but that this warming itself also reduces calcification once it gets above a certain threshold.

“Although there was a wealth of information known about how certain organisms would fare under climate change, coral reef growth is not just the product of coral calcification and survival. Calcifying red algae, known as coralline algae, glue these reefs together and even form their own reefs in certain places in the world’s oceans.

“While corals are highly susceptible to ocean warming, coralline algae are more vulnerable to ocean acidification. Coral reef growth is also dictated by the removal of this calcium carbonate through either bioerosion—living organisms eating the reef—or the dissolution of sediments that help fill in the cracks between larger pieces of calcium carbonate.

“Both processes are likely to accelerate under ocean acidification and warming. However, no one study had put these processes together quantitatively previously.”

There are thousands of coral reefs around the world, each comprising different proportions of corals and coralline algae, with different types of bioeroders, such as parrotfish, sea urchins, and cyanobacteria, and different rates of sediment production.

The study used data on net calcification, bioerosion, and sediment dissolution rates measured or collated from 233 locations on 183 distinct reefs, 49 percent of them in the Atlantic Ocean, 39 percent in the Indian Ocean, and 11 percent in the Pacific Ocean.

This was then modelled against three Intergovernmental Panel on Climate Change emissions scenarios for low-, medium-, and high-impact outcomes on ocean warming and acidification for 2050 and 2100.

Dr Cornwall says their projections show most coral reefs will be unable to maintain growth from carbonate production by the end of the century under the medium- and high-impact scenarios. Even under the low-impact scenario, reefs will suffer severely reduced accretion rates.

“We forecast mean global reef net-carbonate production under these three pathways will decline by 76 percent, 149 percent, and 156 percent respectively by 2100.

“While 63 percent of reefs are projected to continue to accrete by 2100 under the low-impact pathway, 94 percent will be eroding by 2050 under the worst-case scenario, and no reefs will continue to accrete at rates matching projected sea-level rise under the medium- and high-impact scenarios by 2100.”

Drastic reductions in carbon dioxide emissions are now needed to give coral reefs the best chance of continuing to accrete in a future ocean, says Dr Cornwall.

“We are already observing global shifts in coral assemblages and severely reduced coral cover due to mass bleaching events. It is very unlikely corals will suddenly gain the heat tolerance required to resist these events as they become more frequent and intense.

“Our only hope for these reefs now is converting to alternatives to fossil fuels as soon as possible.”

Dr Christopher Cornwall has co-written an article about the study for The Conversation, which can be republished for free under Creative Commons: https://theconversation.com/rising-co2-emissions-will-halt-coral-reef-growth-without-action-160251

Researchers illuminate a role for moonlight in fisheries management

A University-led study shows how the lunar cycle influences the behaviour of larval fish predators and prey and as a result growth rates.

Published 9 February 2021

The phases of the Moon could be harnessed to improve the management and conservation of fisheries around the world.

Research by Te Herenga Waka—Victoria University of Wellington’s Professor of Ecology Jeffrey Shima and colleagues shows the brightness of the moonlight plays a major role in the growth of larval fish just below the sea surface.

By factoring the reliable 29.5-day patterns of the lunar cycle into existing models, fisheries management could be made more sustainable.

Professor Shima, who is in the School of Biological Sciences, says incorporating nocturnal illumination into fisheries models, which already include environmental variables like temperature and primary productivity, would be relatively simple.

The researchers’ newly published paper in Proceedings of the Royal Society B“Lunar rhythms in growth of larval fish”, studied the daily growth rates of the sixbar wrasse (Thalassoma hardwicke) around the island of Mo’orea in French Polynesia.

They found the “best” nights for the sixbars were near the last-quarter moon, when larval fish grew about 0.012mm a day more than average.

On the “worst” nights, near the first-quarter moon, they grew about 0.014mm a day less than average.

“We think the difference is due to the relationship between the sixbars’ prey and predators. Zooplankton—potential prey—respond quickly to the arrival of darkness, while micronekton, which hunt larval fishes, may take much longer to reach surface waters from the depths.

“So prey availability for sixbars in surface waters may be hindered by early nocturnal brightness, while the arrival of predators may be held up by late nocturnal brightness.

“As a result, growth may be worst at the first-quarter moon because prey are suppressed but predators are not, while it may be best at the last quarter because predators are suppressed and prey are not,” says Professor Shima.

Predicting marine population dynamics remains largely unreliable, even after more than 100 years of research into what causes variations in the growth and survival of larval fish.

“Considering some of the important biology that happens at night may improve our forecasting ability and lead to better management recommendations.

“Given we struggle to make such predictions in today’s conditions, it becomes even more complicated when we introduce future climate scenarios to the mix.”

Professor Shima says the findings are also relevant to fisheries in temperate zones.

“These vertical migrations of prey and predator have a global distribution and appear to be affected by moonlight in the same way everywhere.

“In an earlier study, we evaluated the effects of the Moon on the growth of larval temperate fish and found a similar effect, although the effect is stronger and more nuanced in our latest paper, most likely because the waters in the tropics are comparatively clear.

“Our findings also hint that other factors which cause night-time illumination of the sea may disrupt marine ecosystems, such as reflection of artificial lights from cities, suspended sediments, and significant changes in cloud cover due to climate change.”

Professor Shima’s collaborators were Professor Craig Osenberg from the University of Georgia, Associate Professor Erik Noonburg from Florida Atlantic University, and Professor Suzanne Alonzo from the University of California, Santa Cruz, all in the United States, and Professor Stephen Swearer from the University of Melbourne in Australia.

They have written an article about their research for The Conversation. It is available for free republication under Creative Commons.

Their research was supported by a grant from the Marsden Fund, which is administered by the Royal Society Te Apārangi on behalf of the Ministry of Business, Innovation and Employment.

Study finds birdsong remains the same after 1080 drops

Researchers find no evidence forests 'fall silent' because poison is killing large numbers of the very birds it aims to protect.

Published 9 February 2021

Claims that forests “fall silent” because birds are killed in such large numbers during 1080 poison drops are unsupported by newly released research by Te Herenga Waka—Victoria University of Wellington scientists.

Aerial 1080 (sodium monoflueoroacetate) operations control introduced mammals such as possums, rats, and stoats that prey on native species, including birds. The introduced mammals are also vectors of bovine tuberculosis and eat significant amounts of native vegetation.

Debate around continued use of 1080 often centres on its potential impact on non-targets, with some groups saying it kills large numbers of the very birds it aims to protect.

Associate Professor Stephen Hartley and Master’s students Roald Bomans and Asher Cook, from the University’s School of Biological Sciences, used bioacoustic monitoring to track the short-term general and species-specific trends of birdsong in treatment and non-treatment areas.

Their study was conducted for a five- to eight-week period before and after three different 1080 drops in the Aorangi and Southern Remutaka Ranges of the lower North Island in 2014 and 2017. Non-treatment sites in the Taraura and Northern Remutaka Ranges were studied for comparison.

The study’s results are in the New Zealand Journal of Ecology.

Overall, the researchers found little evidence of short-term negative effects on native bird communities.

After the 2014 Aorangi operation, the mean prevalence of birdsong increased slightly in treatment sites, while it remained at near-identical levels in non-treatment sites during the same period. In the 2017 Aorangi operation, birdsong decreased in both treatment and non-treatment sites, but there was no evidence this was connected to 1080 in treatment sites.

In the 2017 Southern Remutaka operation, birdsong actually increased in treatment sites two to six weeks after 1080 was dropped, whereas birdsong decreased in non-treatment sites.

In all cases, both increases and decreases were minor.

Of nine native bird species studied for specific impact, five showed no impact, three showed increases in birdsong after at least one operation, and one (the tomtit) showed an increase, a decrease, and no change.

One introduced species, the chaffinch, showed a very slight decline after one of the three operations, which might plausibly be linked to 1080, as this species is known to eat grains, and the toxin is delivered via cereal baits.

Interpreting the findings, Associate Professor Hartley says: “We know from previous work that most native New Zealand forest birds benefit in the years immediately following effective mammal control. This study confirmed that modern 1080 operations do not cause forests to go silent, and that few, if any, native birds are suffering short-term adverse effects. Regrettably, without appropriate control of introduced mammals, population declines and extinctions of Aotearoa’s native and unique biodiversity will continue.”

The study was part-funded by Tbfree NZ.

Impact of wolves’ reintroduction on pumas has lessons for predator-free NZ

Seeing how pumas have been affected by recently re-established wolves in North America may help Aotearoa develop a more effective Predator-Free 2050 programme.

Published 12 January 2021


Te Herenga Waka—Victoria University of Wellington’s Associate Professor Heiko Wittmer says lessons from observing competition between the two predators at the top of the food chain in a United States national park should be taken into consideration here.

That’s in spite of our top predators—invasive mammals such as stoats—being much smaller.

Associate Professor Wittmer, from the School of Biological Sciences, says the research in and next to Wyoming’s Grand Teton National Park showed interactions between species on the same “trophic” level of the food chain—determined by their feeding behaviour—could be just as important as those between levels.

“In New Zealand, we don’t have comparably sized apex predators in our terrestrial ecosystems. However, we have a range of invasive mammalian predators, such as stoats and rats, that occupy the apex predator position in a similar way to wolves and pumas.

“We are embarking on a predator-free strategy where we will manipulate the abundances and interactions of a range of top predators. Our research shows that changes within trophic levels and resulting changes in species interactions, such as competition, will likely have important follow-on effects as well, particular if one species is managed and the other isn’t.”

In a recent paper in Proceedings of the Royal Society B, Associate Professor Wittmer and co-authors highlighted how reintroducing wolves in Grand Teton National Park negatively affected pumas.

The Grand Teton area gave researchers a “wonderful opportunity” to study puma population dynamics using a unique 16-year data set, he says.

“In particular, we were able to look at the effects wolves might have on pumas. Wolves were reintroduced into this system north of our study area in Yellowstone National Park and then naturally dispersed into our study area, where they had been absent for at least 80 years or so.

“We found the effect of re-established wolves explained most of the observed decline of the puma population in our study area, and it explained it better than other variables we looked at, such as food availability or hunting.

“That was due to quite complex sideways species interactions between pumas and wolves, which included direct mortality of kittens and increased starvation of juvenile pumas.”

Interactions within trophic levels need to be understood before New Zealand implements conservation and management strategies, particularly in systems where species are either reintroduced or heavily controlled or even removed, says Associate Professor Wittmer.

“That is exactly what we are planning on doing with Predator-Free 2050. We have demonstrated we are quite good at reintroducing our native birds to predator-free offshore or mainland islands, but now we are proposing to completely eradicate seven of the most damaging invasive species we have in our ecosystem.

“We know a lot about how these species affect our endangered bird populations, but we don’t really know what is going to happen when we are removing or controlling only some of those species but not others.

“Take rats and mice. The relationship between them is complex and includes competition for food, and at times rats kill mice.

“What we are doing right now is proposing to remove rats from the ecosystem, but not mice. So will we see a mice eruption afterwards because they are now freed from the competitive interactions with rats? We just don’t know.

“Both rats and mice have negative effects on native species. But will there be benefits from removing rats for our rare invertebrates, such as weevils or wētā, if mice numbers increase because they are no longer competing with rats? It highlights that all these systems are highly complex.”

Associate Professor Wittmer is now investigating how scavengers can affect predators in North America and then plans to look into New Zealand ecosystems and apply lessons from overseas.

He hopes increased long-term research funding of 10 years or more will become available in New Zealand.

“Understanding and teasing apart complex species interactions is difficult and requires long-term data. Until we make an investment into make long-term studies, it will be difficult to address topics that require research over many years.”