Cities near the equator hold 42% fewer bird species than nearby natural areas
McGill researchers found urban areas near the equator hold 42% fewer bird species than natural ones nearby, versus 12% at 65 degrees latitude. The tropics' usual lead in species richness is therefore smaller in cities.
The Scientist · Science desk
Three figures. Near the equator, urban areas held 42% fewer bird species than nearby natural areas. At 65 degrees latitude they held 12% fewer. The global figure was 32% fewer.
| Figure | Value | Note | Claim |
|---|---|---|---|
| Urban vs nearby natural areas, near the equator | 42% fewer species | 2 | |
| At 65 degrees latitude | 12% fewer species | 4 | |
| Global figure | 32% fewer species | 3 |
What happened
- Averaged over the globe, urban areas held 32% fewer bird species than nearby natural areas, between the equatorial and 65-degree figures.
- The team drew on eBird, a citizen-science database created at Cornell University, covering more than 10,000 bird species across five continents.
- The team sorted its map cells into urban, suburban and natural using human population density and the degree of landscape modification.
- The researchers said the extra tropical loss comes partly from more intense urbanization there and partly from tropical species coping less well with change.
Why it matters
- exposure A 42% loss near the equator removes more species per area than a 12% loss at 65 degrees, because natural tropical land starts with more species.
- decision For city planners, green space is the lever the authors name: they call such strategies "hopeful measures", and cities with considerable green space saw less decline.
- constraint A species count does not show which birds are missing or how the rest interact, and the team says its next work covers predation and pollination.
The latitudinal diversity gradient is the tendency for biodiversity to rise toward the tropics [1], and the paper's title says urbanization "weakens" it in birds [7]. The reported averages bear that out. An urban area near the equator keeps 58% of the species found on nearby natural land, and one at 65 degrees keeps 88% [15]. Divide the first by the second and the ratio of tropical to high-latitude richness inside cities comes to about 0.66 of its value on natural land [16], a cut of roughly a third [17].
That calculation takes 42% and 12% as the average loss at each latitude, which is how the source reports them [2][4]. It covers urban cells only, and the report does not say how much land those cells take up. Within them, the numbers fit the paper's verb better than the phrase senior author Anna Hargreaves used. "And now, one of Earth's most prominent, obvious biological patterns is almost being erased due to urbanization," she said [6].
Earlier work on the gradient used smaller, more localized data sets [9]. Here, in our view, the completeness filter is the control for uneven birdwatching effort. "We downloaded the data and divided the world into square-kilometer grid cells, only including cells where we had enough eBird data to be confident we were capturing at least 95% of the diversity in each cell," said Jory Griffith, the graduate student who led the analysis [10]. Cells that failed the test are not in the estimate [10]. The thing this doesn't tell you is whether thinly watched tropical cities lose species at the same rate.
What to watch
- A breakdown of how much of the tropical gap comes from urbanization intensity and how much from species tolerance, since the report says only 'partly' for each.
- The share of land the urban cells cover, which would show how far 'almost being erased' applies beyond cities.
- A replication on data other than eBird, which would test the 95% completeness filter.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence68
- Adoption
- Insufficient
- Hype gap+20
- Incentives
- Insufficient
- Confidence65
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
The latitudinal diversity gradient is the tendency for biodiversity to increase toward the tropics.
- [2]
On average, urban areas near the equator contained 42% fewer bird species than nearby natural areas.
- [3]
The comparable global figure was 32% fewer species in urban areas than nearby natural areas.
- [4]
At 65 degrees of latitude, urban areas contained 12% fewer bird species than nearby natural areas.
- [5]
The researchers said the disproportionate loss is driven partly by more intense urbanization in tropical cities and partly because many tropical bird species are less able to cope with changing environments.
- [6]
"And now, one of Earth's most prominent, obvious biological patterns is almost being erased due to urbanization," said Anna Hargreaves, senior author and professor in the Department of Biology.
- [7]
The paper is Jory Griffith et al., 'Urbanization weakens the global latitudinal diversity gradient in birds', published in Proceedings of the National Academy of Sciences (2026).
- [8]
The study looked at more than 10,000 bird species across five continents using eBird, a citizen-science database created at Cornell University that allows users to record bird sightings.
- [9]
Previous research on the latitudinal diversity gradient has used smaller, more localized data sets.
- [10]
"We downloaded the data and divided the world into square-kilometer grid cells, only including cells where we had enough eBird data to be confident we were capturing at least 95% of the diversity in each cell," said Jory Griffith, the graduate student who led the analysis.
- [11]
The researchers classified each cell as urban, suburban or natural, based on human population density and the degree of landscape modification, and compared diversity patterns across the three categories.
- [12]
Hargreaves said the intensity of urbanization had a marked effect, noting that suburban areas and cities with considerable green space saw less of a decline.
- [13]
The researchers suggest such urban planning strategies as preserving green space are "hopeful measures" that might allow birds and other species to share space with humans.
- [14]
The team is now working to understand how changing patterns of diversity affect interactions among species in cities, like predation and pollination.
- [15]
Urban areas near the equator keep 58% of the species of nearby natural areas, and urban areas at 65 degrees latitude keep 88%.
- [16]
The ratio of tropical to high-latitude richness inside cities is about 0.66 of its value on natural land.
- [17]
A ratio of 0.66 is a cut of roughly a third in the tropical-to-high-latitude richness ratio within urban cells.
- [18]
Because the gradient means natural tropical land holds more species than natural land at 65 degrees, a 42% loss near the equator removes more species per area than a 12% loss at 65 degrees.
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Sources
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Topics
- BiodiversityFollow
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Entities
- McGill UniversityFollow
- eBirdFollow
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- Proceedings of the National Academy of SciencesFollow