Hailey
Cities are usually talked about in terms of people—where they live, how much they earn, and what kind of lives they lead. But what if the same city divisions also affect animals? In St. Louis, Missouri, a single road called Delmar Boulevard does exactly that.
This famous street does not just divide neighborhoods by income and race. New research shows it is also dividing squirrels, changing how they move, live, and even how their genes look over time.
This story shows how human inequality can quietly shape urban wildlife, reminding us that what we build for ourselves also impacts the animals living around us.
What Is the Delmar Divide?
Delmar Boulevard runs east to west through St. Louis. On the north side, most residents are from lower-income Black communities, and the area has more vacant lots, older buildings, and fewer public investments.
On the south side, residents generally earn more money and live in well-maintained, green, gated neighborhoods.
This sharp difference has been called the Delmar Divide for decades. It exists because of past policies like redlining in the 1930s and white flight in the 1940s. These policies shaped where people could live and how much money was spent on different areas.
How Scientists Studied Squirrels in the City
Urban ecologist Elizabeth Carlen from Washington University in St. Louis wanted to know something new:
Did these human-made divisions also affect animals?
To find out, she studied eastern gray squirrels, a very common animal in the city.
How the Research Was Done
Carlen and her team collected data from squirrels across both sides of the city. Their work included:
- Setting safe traps with peanut butter and walnuts
- Collecting roadkill samples when possible
- Measuring squirrel size and health
- Taking fur, photos, and small tissue samples for DNA testing
She compared the squirrels’ genetics using methods similar to popular ancestry tests.
What the Research Discovered
The results were surprising. Just like people in St. Louis, squirrels are divided by Delmar Boulevard.
Squirrels from North St. Louis and South St. Louis showed different genetic patterns. Scientists could tell which side a squirrel came from just by looking at its DNA.
Movement Differences Between North and South
Carlen also studied how squirrels move across the city.
| Area of St. Louis | Squirrel Movement | Main Reason |
|---|---|---|
| North Side | Wider movement range | Fewer gates and barriers |
| South Side | Limited movement | Gated areas and heavy traffic |
| South Side | Higher road risk | More cars and busy roads |
Squirrels in wealthier southern neighborhoods tend to stay in smaller areas. Fences, gates, and busy roads block their movement. This increases the risk of road accidents and may lead to inbreeding over time.
On the north side, squirrels move more freely because there are fewer physical barriers.
Why Human Design Affects Animals
Many gated communities are built to improve safety and privacy. But these same features block animal paths and push traffic onto main roads. More cars mean more danger for animals.
Carlen explains that income, race, and traffic patterns are connected. Where people with higher incomes live, there are often more cars, wider roads, and gated streets—all of which change how animals survive.
She believes environmental justice and social justice are deeply linked.
Similar Wildlife Studies Around the World
This type of research is growing globally. In Poland, scientist Marta Szulkin from the University of Warsaw studies how urban living affects birds. Her research shows that city life can change bird colors, health, and even gut bacteria.
In 2025, Carlen and Szulkin co-wrote a study showing how politics, war, and social divisions can break up animal habitats worldwide. Similar studies also show how urban inequality affects coyotes, changing where they travel and how they behave.
What This Means for the Future
Carlen wants to study other animals like raccoons and mice next. Her work sends a clear message:
What humans do to cities does not stop with humans.
Every fence, road, and policy decision shapes the lives of animals sharing our space.
The Delmar Divide is more than a social boundary—it is an ecological one. This research proves that urban inequality affects both people and wildlife. Squirrels in St. Louis now carry genetic signs of human-made borders, showing how deeply city planning impacts nature.
If cities want healthier ecosystems, they must think about fairness, access, and design for everyone—humans and animals alike. Protecting wildlife begins with creating more equal, open, and thoughtful urban spaces.