Urban Rewilding Makes Cities More Biodiverse And Better For Our Health

Forbes

05-06-2025

Two new studies show that successful efforts to bring animals back into global cities come with widespread benefits
The reintroduction of kākā to Wellington is just one of several successful programs designed to ... More re-wild the world's cities. Other research suggests that easy access to biodiverse regions improves human health
The kākā (Nestor meridionalis) is a large parrot found only in Aotearoa New Zealand. Its olive-brown plumage, grey head, and red-orange underwing and belly mean that it can easily blend into dense forest canopies. Its agile wings allow it to weave silently through tree trunks and branches. And thanks to its strong beak and claws, the kākā is a skilled forager, eating everything from insects and seeds, to nectar and fruit.
The first time I ever saw a kākā in person was not in a native forest, as you might expect. It was in a hilly part of New Zealand's capital city, Wellington (Te Whanganui-a-Tara), a short walk from a busy road. Their presence is the result not of luck, but of a decades-long conservation effort that's a story in itself. At the heart of it is a fenced, 225-hectare sanctuary called Zealandia Te Māra a Tāne. In 2000, it became 'the world's first zone in an urban environment free from introduced mammals.' Two years later, less than ten captive-bred kākā were introduced to the sanctuary with the aim of breeding them – the first time the birds had been seen in the city in close to a century. By 2018/19, that population had swelled to over 1,000 kākā, and it spilled out into the wider city. Today, it's relatively common to see (and hear) these intelligent parrots socializing in flocks, or if you're very lucky, on your balcony.
Looking after our urban native birds* has become a city-wide obsession. Alongside Zealandia, the department of Conservation, the city council, and national organizations like Predator Free NZ, volunteers work to restore native plants in the city's numerous reserves and parks, to provide habitat and food for the birds. Traps to catch rats, possums, and stoats are scattered across key parts of the urban landscape, with hundreds of locals offering their gardens as trapping sites.
All of their effort is paying off. Between 2011 and 2024, annual counts of kākā increased by 170%, and for kererū (the NZ wood pigeon famed for getting 'drunk' on fermented fruit) the increase was a staggering 243%. In the same period, populations of my two favorite birds, the tūī (Prosthemadera novaeseelandiae) and pīwakawaka (NZ fantail) have increased by 93% and 37% respectively. In other parts of city, kiwi are successfully being reintroduced.
The remarkably effective 8.6km-long fence that encloses the Zealandia sanctuary is made of tight, ... More mouse-proof wire mesh which extends into the ground. Its height (2.1-2.4m) and rounded cap help to ensure that introduced mammals and predators cannot enter by climbing, either. At 25 years old, the fence is nearing the end of its lifespan. Plans are underway to begin replacing it
Wellington is not the only city working to reintroduce animal (fauna) species to its urban jungle. A new paper from a group of Australian ecologists, published in the journal Bioscience, looked specifically at efforts to reverse unprecedented biodiversity decline through urban rewilding.
While there is no singular definition of the term 'urban rewilding' – it has been adapted and changed over time – these authors offer their own rather wordy version: 'the reintroduction of locally extirpated, missing, or surrogate faunal species into habitat patches, parks, and reserves within or adjacent to human commercial or residential areas.'
With that description in mind, the ecologists searched existing scientific databases for real-world examples of successful urban rewilding. Of the 120 relevant studies they identified, two-thirds focused exclusively on vegetation, and just 17 'documented active terrestrial faunal species re-introductions into urban environments.'
Wellington's work with kākā was one of them. Some of the other successes include a project to reintroduce beavers to London for the first time in 400 years, peregrine falcons now nesting on Chicago high-rises, the oriental pied hornbill breeding in Singapore, and a baby platypus spotted in a Sydney park a few months after five pairs has been reintroduced.
The aim of urban rewilding typically goes beyond the recovery of particular species. Community engagement, education, and cultural restoration all play roles in these projects, as lead author Dr Patrick Finnerty explains, 'They reconnect people with nature – an antidote to what researchers call nature deficit disorder. In today's urban environments, many children can name hundreds of brands but often not a single native bird or mammal. Bringing wildlife back into daily life improves mental health, fosters environmental stewardship, and reminds us that nature isn't something 'out there'.'
A family of 5 beavers, 2 adults and 3 kits, were released back into Paradise Fields reserve in west ... More London, for the first time in 400 years.The project is part of the London Mayor, Sadiq Khan's, 'Rewild London' fund. (Photo by)
There is a group of social scientists in China who would agree with Finnerty's conclusions on health. Their (unconnected) paper, published in the journal Nature Cities just a few days after the Australian one, looked not at urban rewilding, but at the accessibility and mental health impact of 'biodiversity-rich recreational areas' close to cities.
There have been a large number of studies which show that having more green areas in a city comes with physical and mental health benefits to its residents. And there's some evidence that the quality of that green space matters, with, for example, wooded areas linked to lower levels of hypertension than a grass lawn. However, understanding the relationship between nature experiences and mental well-being is complex, and is likely influenced by how easily someone can 'access' nature – is it on their doorstep, or do they need to travel long distances to reach it?
This study, which looked at 9,034 cities scattered around the world, aimed to 'bridge [the] divide between biodiversity conservation and public health research.'
In each city, the researchers analyzed how accessible and affordable it is for residents to reach biodiverse regions. Their second research question was around the mental health impact of visiting biodiversity-rich recreational areas – they wanted to know how cost-effective such access can be as a public health intervention in the treatment of anxiety and depression.
Having easy access to lush, green forest can improve city-dwellers' mental health (photo from Long ... More Bay Coastal Okura Track in Auckland).
They found that 96.7% of cities are within a two-hour journey to a biodiversity-rich recreational area, but that accessibility was not evenly distributed. Cities in Europe, Oceania, and North America had the best access to such areas, with 85% of them able to reach one within 15 min. For the majority of cities in South America and Asia, travel times were closer to an hour. The lowest accessibility (and highest travel cost ratios) was seen in cities in sub-Saharan Africa, West Asia and Southeast Asia, where many residents are more than 4 hours away from one of these areas.
In terms of using biodiversity-rich recreational area visits as a public mental health intervention, the researchers found that it would be 'very cost effective' in 242 cities and 'cost-effective' in 1206 cities. Most of these cities were in high-income countries in Europe, North America and South America.
But they say that if travel costs were excluded from the analysis, the benefits of accessing biodiversity-rich recreational areas would be a cost-effective mental health intervention in every city they studied. In other words, if these areas were easier to reach, everyone would benefit.
The authors conclude, 'Realizing the untapped potential of accessible biodiversity-rich recreational areas to cities could substantially enhance their benefits via a number of interventions. For instance….the restoration and rewilding of degraded areas near cities…[and] progressively expanding protected areas.'
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* The focus is on birds is because New Zealand's only native mammals are bats and marine mammals (like seals, dolphins and whales).