Humans are the leading cause of species declines and extinctions across the planet. There is no doubt about that. But more and more, I hear about people’s close encounters with urban wildlife, including my own. Just the other day, I was walking my dogs on the greenway here in Raleigh and on our way back, we came across four deer in the mowed grass just before you turn onto a somewhat busy road. We actually saw the deer when we started our walk, but they were in the creek on the other side. My coyote-sized, loud dogs barked at them then, but they didn’t budge. Then one of the deer did move, but walked towards us, not away. We were about 15 m away from them overall. I was struggling just to keep my dogs’ leashes in my hands, while the deer were mostly unfazed through all of the ruckus. The deer never left their spot while my dogs were barking incessantly even as they were out of sight.
It seems like encounters like the one I described above are happening more and more. A lot of people think that such close encounters like these are becoming more frequent because we have destroyed animals’ habitats, leaving animals unexposed with no where to go and therefore easier to see. But in some areas, urban wildlife are appearing in places that they haven’t lived for a very long time. For examples, coyotes now thrive in downtown Chicago and in New York City, cities that have been heavily developed for hundreds of years.
On the eMammal project that I am a part of in Raleigh, we have been training citizen scientists to set up camera traps in their backyards for several years. It seemed like we were getting more mammals captured on camera traps in the more suburban settings than the rural. I work with teachers and they set up camera traps at their schools. I worked with one at a school in suburban Raleigh, right across the street from a large outdoor shopping mall. Normally, when you think of urban wildlife, you think of squirrels, raccoons, and opossums. I couldn’t believe we were getting grey foxes and coyotes in the extremely small patch of trees, nothing large enough to be considered a forest, right behind the school. A few years ago, we decided to officially study this and compare how the mammal community (mammals larger than a chipmunk) of human-dominated areas matched up to the wild.
Large-scale Urban Mammal Study
We conducted a large-scale study investigating the abundance, species richness (number of species), and diversity of urban wildlife, specifically mammals you can capture on a camera trap, across the rural-urban gradient here in Raleigh, NC, and with our partners at the Smithsonian in Washington DC. If you think about a city, there tends to be a downtown area which is the most urbanized and “hostile” to wildlife (fewer green spaces and lots of pavement). Surrounding the city is a concentric ring of circles of decreasing urbanization.
We worked with volunteers to set camera traps in their backyards across these different zones of urbanization from urban to suburban, exurban, rural, and wild areas using heat-and-motion-triggered camera traps. We also included three other plot types within each development zone to look at the impacts of habitat. These included large forests, small forest fragments, and open areas. We ran this study for several years, deploying cameras in nearly 1,500 locations across the two cities.
What Did We Find?
We expected to find the declines in diversity, richness, and abundance typically associated with human development, but were surprised to find that urbanization did not appear to impact the mammals we detected with camera traps. Most animals were photographed across all levels of development and with most detections in the suburban/exurban zones rather than rural/wild areas. No species were found only in the wild areas.
We also found no significant decline of species diversity or richness from suburban to wild areas. However, we did find in DC, that diversity was lower in the urban zones. Because it is difficult to run camera traps in truly urban environments due to the likelihood of theft and the high volume human and vehicle photos, we had the fewest locations in truly urban areas, and these locations were only in DC. It’s difficult to know if the declines are a real effect, or if they are due to small sample size. (FYI-I did see a grey fox in downtown Raleigh on a dinner date last month. Just sayin’.)
The species that seems to have the hardest time adapting to urbanization was the bobcat, which was detected infrequently in suburban/exurban areas in both DC and Raleigh. There was also some variation within species across the two cities such as chipmunks, being commonly found in the suburban areas of Raleigh compared to mostly in the wild areas of DC. Although bears are actively discouraged from colonizing Raleigh, our study found them to be within in exurban, rural, and wild areas in DC.
Carnivores tend to be the animals that are most impacted by urbanization, yet our results showed that green space was more important than development. In other words, as long as carnivores had green space, whether it was large or small, they could survive in all development zones. The mammal diversity found within peoples’ yards was higher or the same as diversity found in large and small forest fragments.
Why are Mammals Urban?
As scientists, we were honestly surprised by these results. We knew there were already mammals living in the developed landscapes of Raleigh and DC, but I didn’t expect it to be higher than or the same as in wild areas and with the full suite of species. There are some good reasons why mammals might even like developed landscapes. First, they might be able to exploit different resources. For example, deer may feed off of your garden, squirrels may come to your bird feeder, or animals may also scavenge from your garbage or compost. However, there are studies that show that urban mammals, like coyotes in Chicago, primarily hunt over scavenge. Our next study actually is investigating this, if accidental or purposeful feedings attract different types of animal residents.
Humans can also provide dimension and structure to habitat. For instance, landscaping and ornamental trees might provide better cover for some animals than more open forests. Such diversity across yards might allow for more individuals to squeeze in.
There might also be some behavioral effect from humans. Hunting is not allowed in the suburbans, in contrast to wild or rural ares. Animals living in more developed landscapes have likely learned this, which is a likely a reason why I can easily see deer on the greenway or that they aren’t scared of my dogs (they learned they are on leash and cannot chase them).
While the results of our study are encouraging for mammals, it is important to remember that these results are NOT the same for other types of urban wildlife. The diversity of amphibians, reptiles, birds, insects, and even other mammals that we can’t capture on camera traps (mammals smaller than chipmunks and bats) decrease in response to development. Additionally, we’ve already driven other large mammals that use to live in the eastern US to extinction (gray wolves and cougars). Despite this, it is promising that many mammals can adapt, and even thrive in developed areas. Our study also reflects the importance of green spaces, even small ones, in helping mammal communities thrive.
While many other studies show diversity declines across other taxa, it’s important to not throw the baby out with the bathwater. Urban green spaces, even for animal groups that decline with increasing development, are important for their survival and can serve as hotspots within a sea of sprawl. If you see wildlife in your yard, consider yourself lucky. To help out the local wildlife in your neighborhood, you can advocate for more green spaces and make your yard friendly for wildlife. I personally find it exciting to know that my neighborhood is wild.
To identify animals in your backyard, use the best field guide out there, Mammals of North America, written by my boss, Dr. Roland Kays!
Finally, check out our video on red fox in suburban Raleigh! Complete with photos of cute, baby red fox pups.