A City Built for People and Birds: Lessons from Gothenburg’s Dense Neighbourhoods

Cities are being encouraged to become denser so that homes, public services and transport networks can serve more people without pushing development farther into undeveloped land, and tightly packed neighbourhoods can also remove the green and blue spaces that wildlife needs. The study 'Building Dense or Compact Cities Without Jeopardizing Biodiversity: Insights from Bird Observations in Gothenburg, Sweden,' published in the journal npj Urban Sustainability, explores whether dense urban growth and biodiversity can coexist.

Researchers Ahmed Hazem Eldesoky, Oskar Kindvall, Meta Berghauser Pont, Ioanna Stavroulaki, Jorge Gil and Nadia Charalambous examined bird communities across Gothenburg and found that dense districts supported fewer species than greener reference areas, while also revealing that well-designed habitats can keep a surprising range of birds inside compact neighbourhoods.

Thousands of Hours of Birdsong Reveal Life Across the City

The researchers studied 30 locations across Gothenburg during the spring breeding season, from 21 April to 16 June 2024. Nineteen sites represented three common urban forms: compact low-rise neighbourhoods dominated by row houses and spacious courtyards, compact mid-rise districts with taller buildings but similar ground coverage, and dense mid-rise areas where buildings occupied a larger proportion of the available land. Eleven reference sites included large parks, woodlands, semi-natural areas and sparsely built neighbourhoods with plenty of vegetation.

Small AudioMoth recorders attached to trees captured bird sounds for one minute every two minutes during periods of strong vocal activity around dawn, morning and evening, producing 10,691 hours of recordings and 239,597 occurrence records. BirdNET, a convolutional neural network system for identifying bird calls, processed the recordings, while an expert ornithologist manually reviewed more than 5,000 detections to remove errors caused by tram noise, overlapping calls and other urban sounds. Records with an occurrence probability below 0.75 were excluded, leaving 230,822 observations representing 61 species from 25 families.

This intensive monitoring allowed the team to measure species richness, meaning the number of species found at each site, alongside species composition, which describes the identities of those birds and how communities differed between locations. Birds were chosen because they are diverse, widely distributed, comparatively easy to monitor and sensitive to environmental change, while their pollination, seed dispersal, pest-control and cultural roles make them valuable indicators of wider ecosystem health.

Greener Reference Areas Hosted Richer and Different Communities

The reference areas contained a median of 33 bird species, compared with 24 across the three dense or compact urban forms, a difference that confirms the biodiversity cost associated with intensive development. Bird-community composition also differed between these two broad groups, with several habitat-sensitive species recorded only in greener locations. Common Reed Warblers and European Nightjars, for instance, depended on environmental conditions unlikely to be found in tightly built neighbourhoods.

Some compact or dense sites supported more species than individual reference locations, showing that high building density does not automatically produce an ecological wasteland. The Lesser Black-backed Gull appeared only in the built-up group, reflecting its ability to use rooftops as nesting places, while other observations showed that uncommon urban birds can occupy dense districts when suitable resources survive.

The three urban forms did not differ from one another in either species richness or community composition. Compact low-rise, compact mid-rise and dense mid-rise sites contained considerable internal variation, yet their bird communities overlapped strongly when compared as separate categories. Building height and ground coverage alone could not explain why one site performed better than another.

Habitat Area and Landscape Connections Matter More Than Building Type

Local natural habitat emerged as the strongest and most consistent influence on urban bird diversity. The researchers measured green and blue habitat within 70 metres of each recorder, matching the distance at which acoustic detections were considered reliable, then calculated structural connectivity by examining how close each location was to surrounding natural habitats across distances ranging from 200 metres to four kilometres.

The best-performing model combined local habitat area with connectivity measured across an 1,800-metre radius. A one-standard-deviation increase in nearby natural habitat was associated with a 16% rise in expected species richness after connectivity was taken into account. An equivalent improvement in structural connectivity was linked to a 10% increase. Connectivity remained statistically important across scales of roughly 1.4 to 2.4 kilometres, a distance that falls within the movement range of many bird species.

Local habitat area was also the main factor associated with changes in which species were present. Habitat diversity, measured through the number and balance of different habitat types, showed no dependable relationship with either richness or composition in the strongest models. The finding suggests that preserving or expanding a meaningful amount of natural space may help birds more than squeezing many small habitat categories into an area without providing enough usable territory.

A Common Tern was found at a dense mid-rise site close to the Göta älv River, where water supplied the resources it needed. A Stock Dove, rarely recorded in urban settings, appeared in a compact mid-rise green space containing old beech trees with nesting cavities and feeding opportunities. These examples indicate that site-specific features can carry greater ecological weight than the surrounding neighbourhood's architectural label.

Dense Development Needs Nature at Several Connected Scales

The results give planners two linked routes for protecting biodiversity. The first is to retain or expand high-quality green and blue spaces inside dense districts, since local habitat area delivered the strongest benefit. The second is to connect constrained sites with larger natural areas through riverbanks, railway embankments, parks, yards, green roofs, vacant land and other spaces that can function collectively as ecological stepping stones.

Targeted measures could provide nesting cavities, breeding areas, native vegetation, food sources and microhabitats for species with particular needs. Placing those resources along movement routes may help birds reach feeding and reproduction sites scattered across the city, while a collection of neighbourhood spaces supporting different species could produce greater biodiversity across the wider urban landscape. Native habitats deserve priority because non-native species may disrupt ecosystems or introduce risks to human health.

The study contributes to the debate between 'land sharing,' where development accommodates nature throughout the built environment, and 'land sparing,' where dense construction leaves larger natural areas intact elsewhere. Gothenburg's evidence suggests that compact development can preserve valuable habitats at the urban fringe while still supporting wildlife internally, provided local natural space, habitat quality and wider connectivity are planned together.

Only birds were examined, three environmental variables were tested, and the work covered one Swedish city during a single spring season. Noise, artificial light, microclimate, vegetation management and interactions among species may also shape urban biodiversity. Passive acoustic monitoring can miss quiet or infrequently calling birds, despite the extended recording schedule and expert validation used here. Research involving additional cities, seasons, monitoring methods, and animal or plant groups will be needed before the patterns can be widely generalised.