by In Sapzurro bay on the Colombia-Panama border, the blue land crab can be found scuttling around human infrastructure, burrowing in the nooks and crannies of the coastal settlement. This species, which can grow up to 15cm and its color ranges from violet to bright cerulean blue, is considered critically endangered or threatened in this region, although it can be classified as invasive elsewhere. It traditionally lived in the region’s rich mangrove forests, many of which are now urbanized – a loss of habitat that scientists have blamed for the crab’s decline.
But when the scientists studied the distribution of the species around the Sapzurro bay, they were surprised to find that it was still successful in areas where there was no vegetation: creeping into grass, banana and coconut plantations, and scouring under concrete structures. Although holes in urban areas were smaller and smaller, he managed to build houses along sewer canals and among houses.
A growing body of research is gathering data on species like this crustacean – learning about threatened wildlife to thrive in urban spaces alongside people.
“We often forget that we are dealing with living animals,” says José Marin Riascos, a marine ecologist at the Corporation Center of Excellence in Marine Sciences of Colombia, which published the study on the blue land crab in April 2024 “It’s not like that. passive, they are active. If you change something, they respond with another change.”
These findings also complicate the long-held idea that cities cannot be hotbeds for animals and plants, and that conservation is something to be done far away, in out-of-touch places with him.
“We’re assuming that when people change an ecosystem, biodiversity habitat is lost,” says Riascos. That’s not always the case, he says. In some contexts, “it’s changing”.
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In general, cities have very negative impacts on wildlife. On average, if there are 100 species in a region, only 25 would be found within the city, and populations can be up to 92% smaller than outside the urban area. But the remaining chunk of wildlife includes some species that are doing better in cities than outside them. This group can provide useful insights into how animals can adapt – or not – to human spaces, but more importantly, how people can adapt their cities to be more wildlife-friendly.
Studies have found that 66 out of 529 species of birds that live in cities are only found in urban areas. In Santo Domingo, Dominican Republic, threatened Hispaniolan parakeets hold their ground in urban green spaces and old buildings. Across North America, great, fluffy owls have found new burrows in cities. Australia’s three endangered species of cockatoos—Baudin’s black cockatoo, Carnaby’s black cockatoo, and the forest red-tailed black cockatoo—are adapted to munching on urban pine forests. In London, peregrine falcons found mimics of tall trees in high-rise buildings.
“This is definitely something we’ve overlooked,” says Erica Spotswood, an urban ecologist at Second Nature Ecology + Design in California. In a study published in 2021 in the Journal of Bioscience, she argues that cities could perform various services for the surrounding wildlife.
That doesn’t mean we have to lose nature and wildlife by building cities and having places to live – we can have both
Kylie Soanes, urban ecologist
“We’ve created cities in places we like, along rivers, along the coast, in alluvial plains, at the bottom of valleys,” says Spotswood, and human choices overlap with those of many species. This means that cities have a wide range of habitats within them, and a lot of diversity.
Urban spaces can be a refuge during times of stress and scarcity in the wild, providing easier access to an abundant variety of resources throughout the year. And cities can help species escape threats to animals in the surrounding landscape – for example by providing refuge for pollinators from pesticides that are systematically spread across agricultural land.
Studies have shown that some different species of native bees are more abundant and diverse in cities than in their surrounding landscapes, and that cities can be hot spots for some pollinators. “Bees are a great example,” says Robert Francis, professor of urban ecology and society at King’s College London. “The growing season for plants is extended in cities, so there are more plants over a longer period and the resources are very good.”
Only in the urbanized coastal waters off South Florida is the small sawtooth fish, once abundant in North American waters, increasing in size, according to one 2020 paper. And studies show that western ring-tailed possums are at risk after finding refuge in residential gardens across Australia, even as they have access to more rural areas.
When builders went to fill an abandoned industrial site in Sydney to build a new stadium for the 2000 Olympic Games, they found the dirty water filled with green frogs and golden bells – chunky, cartoonish amphibians. endangered throughout Australia.
“Everyone thought it was a horribly degraded urban site, but it turned out to be critical habitat for these hanging frogs,” says Kylie Soanes, an urban ecologist at the University of Melbourne.
Like this frog, for the “vast majority” of threatened species found in cities, the city is their home range with people built on top of it. But this also means that the city is the last place where the species – a category of animals that Soanes calls “last chance species” – has a foothold, so urban spaces are a vital opportunity to protect and preserve them.
In order to do that, the assumption that cities cannot be places of conservation, she says, needs to be strengthened, and to recognize that they provide opportunities for intense supervision by people.
Related: The world’s cities go head-to-head in the race to see the most urban wildlife
“City building and housing doesn’t mean we have to lose nature and wildlife – we can have both in the same place,” says Soanes. She points out that she grows more wildlife-friendly plants in private gardens, and that more wildlife-supporting infrastructure, such as bird nesting boxes, bee hotels and frog ponds outside homes and around the city, is “blurring the lines” between urban and natural.
In Brazil, the Macacos Urbanos Program has built aerial wooden and rope bridges across roads to help prevent monkeys from electrocuting themselves by swinging on power lines. In the UK, building product manufacturers have started making “quick bricks” – plastic bricks designed to allow nesting nests, and bus stop roofs have been converted into small patches of grass known as “bee stops”.
“It’s just saturating the city with biodiversity-friendly things: green space and green infrastructure,” says Francis, who lives in a housing estate where some of the buildings have bat nesting boxes. However, he cautions that it is too early to know whether these small changes make significant differences to animal populations in cities, and on a large enough scale to support population growth over generations and to the surrounding landscapes. repopulate all too,” or if it’s just a tiny little difference”.
But, says Francis: “Recent research on cities has revolutionized our understanding of urban ecosystems.”
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