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Reports on Bird Biodiversity Reveal the Impact of Redlining in Cities

Six birds sit on a power line and one bird sits on a lower power line in front of a blue and cloudy sky.

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The foundation of various biodiversity conservation initiatives heavily relies on public records of bird observations. However, in the United States, the majority of bird-watching data collected through crowdsourcing are from predominantly white and wealthy neighborhoods, while there is a noticeable absence of data from historically redlined neighborhoods. Recent studies have revealed that this is a result of the racially discriminatory housing practices in the 20th century, which continues to impact current efforts in biodiversity conservation.

Diego Ellis Soto, who led the recent study, stated that even after 100 years, redlining in 1933 remains a significant factor in the limited availability of bird data in previously redlined regions. This highlights an environmental justice issue that is often overlooked in conservation decision-making.

Ellis Soto, a doctoral student at Yale University, stated that providing fair and equal representation and access to nature for citizens and residents of the United States is a crucial aspect of federal policy. However, there is currently a significant gap in this area.

The birds exist, but the data is missing.

During the 1930s, the HOLC evaluated neighborhoods based on their perceived level of investment security using a rating system of A (green), B (blue), C (yellow), or D (red), with D being the lowest rating. These boundaries were largely determined by the race and socioeconomic status of residents, resulting in poorer and racially diverse neighborhoods receiving lower grades of C or D, while wealthier and predominantly white neighborhoods received higher grades of A and B. This discriminatory housing practice, commonly referred to as redlining, continues to have lasting effects today, including ongoing segregation in housing, wealth disparities, health inequalities, and unequal access to green spaces and their benefits.

Ellis Soto and his team aimed to explore the impact of past zoning practices based on race on our knowledge of urban biodiversity. They selected documented bird observations as their measurement, as they make up the bulk of biodiversity information.

Previously, areas with an A-grade had a sampling density that was more than double that of areas with a D-grade.

According to Ellis Soto, birds are the most extensively researched living beings on our planet due to the popularity of bird-watching as a recreational activity.

The scientists collected approximately 12.3 million reports on bird biodiversity, which were georeferenced and spanned from 1932 to 2022. This included data from the widely used bird watching app eBird. They compared these records with nearly 10,000 neighborhoods defined by HOLC in 195 cities across the United States. The researchers also calculated the density and completeness of bird sampling, while taking into consideration the amount of green space in each neighborhood. This allowed for a fair evaluation of bird biodiversity in various urban environments.

In various cities throughout the country, regions that were once classified as A-grade had a sampling density that was more than double that of regions previously classified as D-grade (approximately 1,600 per square kilometer compared to around 700 per square kilometer). 13% of D-graded areas had no recorded bird sightings, while only 8% of A-graded areas lacked any bird records. The regions with the most significant lack of biodiversity were those classified as C and D-grade.

A map of the contiguous United States with multicolored dots marking major cities. Inset charts show that in Los Angeles, Detroit, and New Haven, Conn., formerly D-graded neighborhoods had the lowest bird sampling density.

Bird sampling density is typically lower in areas that were once redlined and higher in neighborhoods that received the highest housing grade in cities throughout the United States. This information was reported by Ellis Soto et al. in 2023 and can be found at under a CC BY-SA 4.0 license.

The team concluded that the HOLC grading system’s rank-order is consistent with the amount of bird sampling that has been done.

Ellis Soto, who resides and attends school in New Haven, serves as a prime illustration of the data disparity. On the grounds of Yale University, there have been numerous sightings of birds reported, totaling in the tens of thousands. According to Soto, if they were to walk just two blocks, they would enter the Dixwell neighborhood, which has a history of being heavily segregated and was once redlined. Despite being only 300 meters away, there is significantly less data on bird sightings in this area. Soto emphasizes that it is highly likely that the same birds seen on campus also fly over this neighborhood.

A chart with four bars that descend, left to right, and are colored green (A), blue (B), yellow (C), and red (D).
The density of reported bird sightings was highest in areas that had been rated A and B grade in the early 20th century and was lowest in formerly C- and D-graded areas. Credit: Ellis Soto et al., 2023,, CC BY-SA 4.0

In September, the findings were published by the researchers in Nature Human Behavior.

Many cities are experiencing gentrification in neighborhoods that were previously neglected. This involves an increase in investment, new businesses, and housing, which often leads to the displacement of long-time residents. While this study did not consider how gentrification may impact data collection, it did find that these once-redlined neighborhoods, now more affluent, still have lower levels of biodiversity compared to areas that were not redlined.

According to Ellis Soto, if gentrification had been taken into consideration, the disparities would have likely been much more noticeable.

As more people participated in these efforts to gather data, previously redlined regions were overlooked.

Additionally, there has been a 36% increase in the reporting gap in the last two decades due to the rise of bird-watching apps that rely on contributions from the public. This means that as more people participate in collecting data, previously excluded areas are being neglected.

According to Ashley Dayer, a researcher at Virginia Tech in Blacksburg, not sampling enough poses various problems for both bird conservation and human communities. This is because eBird data is frequently utilized for conservation planning and prioritization.

The Biden administration has launched various initiatives, including the Justice40 Initiative and the America the Beautiful Initiative, which allow federal and state governments to allocate conservation funding to areas that are vulnerable to environmental deterioration, specifically those that have been overlooked in the past. These initiatives utilize the EPA’s Environmental Justice Screening and Mapping Tool, which takes into account factors like air quality, proximity to Superfund sites, and access to clean water.

How can we safeguard something that we are not aware of having?

The Environmental Protection Agency tool does not include measures for biodiversity, so government officials use statistical models to allocate funds to regions with a high risk of species decline. According to Ellis Soto, having accurate records of bird locations is essential for understanding biodiversity. Rather than relying on unfairly gathered data, it is important to know the actual whereabouts of birds in order to protect urban biodiversity.

The scientists posed the question, “How can we safeguard something that we are not even aware exists?”

Expanding the Scope of Birdwatching

Previous studies by Dayer have revealed that the majority of eBird participants (95%) are white, which is significantly higher than the representation of white individuals in the U.S. population (77%). It is believed that these bird enthusiasts tend to engage in their hobby within their local communities, which are less likely to have been affected by historical redlining policies.

According to Ellis Soto and fellow researchers, the solution to the problem does not involve sending privileged, older, and white birdwatchers to areas with limited data. Instead, they suggest that educating K-12 students and involving the community in their local neighborhoods is crucial.

If individuals do not see others who resemble them participating in (e)Birding, they may not consider it to be an activity for them and may not become involved.

Dayer concurred with this evaluation. She stated, “The answer isn’t simply to have the current eBird users explore these underrepresented regions.” She believes that involvement in birdwatching in general and specifically eBird likely offers advantages in scientific knowledge, physical well-being, and mental wellness, which should be accessible to more than just wealthy white birders.

“We need to prioritize addressing the disproportionate representation of white participants in eBird and tackle underlying systemic issues and barriers that hinder participation,” she stated. “If individuals do not see those who resemble them involved in (e)Birding, they may not perceive it as an activity for themselves and therefore, may not become involved.”

—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer

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Citation: Cartier, K. M. S. (2023), Bird biodiversity reports reflect cities’ redlined past, Eos, 104, Published on 5 October 2023.
Text © 2023. The authors. CC BY-NC-ND 3.0
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