A city is more than its buildings
Look up from a busy pavement and a peregrine may be using a tower as a cliff. Look down beside the railway and a strip of rough vegetation may be feeding bees. A city is an improbable nature reserve, assembled from rooftops, gardens, rivers, vacant lots and scraps of land that planners may never have intended as habitat. The question is not simply whether wildlife can live among people. It is which wildlife, in what numbers, and for how long.
Peregrines are an arresting example. The birds traditionally nest on cliffs and rocky ledges, but tall urban buildings can offer similar nest sites.¹ A city supplies perches and prey as well as hazards. Their success should not persuade us that urbanisation is harmless: a species that can use concrete ledges tells us little about a woodland specialist that needs continuous tree cover or an insect that depends on a particular plant.
The surprising value of untidy ground
People often judge a green space by its neatness. Wildlife has different criteria. An abandoned industrial site may contain bare soil, rubble, flowering plants, damp hollows and patches of scrub within a small area. That mixture provides nesting, basking and feeding places for different invertebrates. Buglife notes that some brownfields hold threatened species and can be among the last wild places available to urban communities.² A smooth lawn may look greener from a distance while offering far fewer ecological opportunities.
Railway land can work in a similar way. Britain’s lineside estate stretches through urban and rural areas, and Network Rail’s biodiversity plan explicitly considers its value as habitat and as a set of wildlife corridors.³ Insects can use sunny banks, flowers and rough vegetation along these edges. Yet a corridor on a map is not proof that every creature can travel it. Roads, fences, lighting and gaps in suitable habitat can interrupt movement, and different species need different kinds of connection. A review of urban connectivity research found that many proposed links have not been tested against actual animal movement.⁴
Gardens, street trees, cemeteries, canals and parks add still more niches. A single garden can offer nectar, shelter and water; neighbouring gardens can become a larger network. The design and management of each patch matter. A mature tree, flowering understory and leaf litter offer different resources from a newly planted ornamental bed. London's urban greening guidance therefore treats biodiversity as a design question, not merely a matter of adding green colour to a plan.⁵
Winners, losers and misleading headcounts
Cities filter nature. Animals that tolerate people, noise and novel foods often do well; species needing darkness, quiet or large unbroken habitat may retreat. A global study drawing on observations from hundreds of cities found that urbanisation selects for particular animal traits across birds, bees, bats, amphibians and other groups.⁶ That is why a lively city can still be missing much of the wildlife that occupied the land before it was built.
Counting species is useful but not sufficient. An urban park might acquire many introduced ornamental plants while losing locally distinctive native species. The total list grows, yet the local ecosystem may become more like parks everywhere else. Research on urban biotic homogenisation describes this tendency towards similar assemblages, although its pattern varies by place and group of organisms.⁷ The better question is whether a city supports healthy populations of species that matter to its region, including the less charismatic ones.
City life also brings specific threats. Bright nights can disrupt nocturnal animals and alter interactions between insects and flowers. Artificial-light research identifies ecological risks, though effects differ by species and lighting design.⁸ Traffic kills animals and fragments habitat. Pollution changes soil and water. Cats, collisions with glass and heat can add pressures. Even conservation measures can misfire: a flower-rich patch mown during peak bloom may lose much of its value, while a poorly placed nest box cannot make up for missing food.
Conservation that survives beyond a photograph
Effective urban conservation starts by asking what is already there. A brownfield should be surveyed before being labelled empty. Existing mature trees, wetlands and connected habitat often deserve protection before new decorative planting is proposed. That approach can be inconvenient where land is scarce, but replacement habitats take time to develop and may not serve the same species. England's biodiversity net gain system seeks measurable improvements from many developments, yet a numerical gain should still be checked against ecological reality on the ground.⁹
Then comes management. Let some grass flower and set seed; retain varied vegetation heights; provide native plants suited to the site; reduce unnecessary night lighting; and keep waterways and green spaces connected where possible. Natural England's design guidance recommends a diversity of vegetation types, including meadows, shrubs and woodland layers, rather than treating every public space as short grass.¹⁰ Choices need to account for access, safety and the species actually present. A useful meadow beside a path is still a public place.
Monitoring matters just as much as planting. Did the target insects appear? Are birds breeding successfully, rather than merely visiting? Can wildlife move between patches? Those questions take repeated observation and local knowledge. They also make room for residents, whose gardens and records can reveal changes that a one-day survey misses.
There is no universal number for how much wildlife a city can support. A city is a changing collection of habitats under pressure from development, climate and human habits. The most hopeful answer is practical: protect the good places already present, make ordinary spaces more hospitable, and judge success by the lives sustained over years. The peregrine on the tower is a thrilling beginning, not the whole inventory.