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Urban Wildlife Bounty

Research reveals cities support a surprising wealth of species

  • Cynthia Berger
  • Animals
  • Jan 26, 2015
I'M STROLLING THE GROUNDS of the New York Botanical Garden, a quiet green space in the noisy heart of the Bronx. The sun is hot, but once I leave the neat, conventional garden beds and enter the Thain Family Forest, the air is cool under old-growth oak and hickory trees. And when the roar of a JFK-bound jet dies away, I can hear catbirds, white-eyed vireos and a kingbird running through their vocal repertoires.

I’m walking the Spicebush Trail with Myla Aronson, a Rutgers University scientist who is the lead researcher on a groundbreaking study of biodiversity in cities across the globe—a study that refutes what she calls the myth of biotic homogenization. “Everyone assumes that because of globalization, cities are all the same in terms of the plants and animals you find there—mostly rats and pigeons,” Aronson says as we stroll. “It is true that biodiversity is much lower in cities than in undisturbed habitats. But it’s much greater than we expected.”

Completed in 2014, the study was a collaborative effort by two dozen scientists from universities and research institutions around the world. During a four-year period, the group looked at studies of bird diversity in 54 cities and plant diversity in 110 cities. The aggregate data reflect what individual researchers are finding at the local scale: encouraging signs that many species thrive in cities. Researchers in France, for example, recently recorded nearly a third of the nation’s 900 wild bee species living in and around the bustling city of Lyons.

Another key finding of the study is that each city seems to maintain its uniqueness—its local flavor—thanks to the variety of native birds and plants living there. I can see that for myself in the Thain forest. Allison Anholt, a Rutgers ornithology graduate student who’s with us on the trail, points out typical city birds (house sparrows and European starlings) but also spots native forest species like the eastern wood-pewee, great crested flycatcher and red-bellied woodpecker—all living in a patch of woodland that is plunk in the middle of the third most densely populated county in the United States.

This forest is also home to other species you might not expect to find in the heart of a metropolis. Jessica Schuler, our tour guide and director of the Thain Family Forest, tells us that researchers have found nine bat species in these woods. “A family of beavers lives down there, on the Bronx River,” she says, pointing to the glint of water in the gorge below the trail. “And recently, my staff spotted a mink!” Another New York surprise came to light two years ago, when Jeremy Feinberg, a Rutgers grad student, found a new species of leopard frog—previously unknown to science—on Staten Island of all places.

New York City is hardly the only big city that supports unexpected wildlife. In Spokane, Washington, for example, Gonzaga University researchers are studying the city’s population of yellow-bellied marmots (below)—animals that usually are found only in remote mountainous areas. Spokane is “unusual in having these marmots thrive among the cars, the bikes, the dogs and the people,” says Gonzaga biologist Elizabeth Addis, who estimates a population in the thousands. She’s investigating whether lower predation rates in the city may help explain the boom.



Nurturing the Wild Side
The finding that cities support unexpected biodiversity meshes with a movement in some cities to deliberately manage their green spaces with biodiversity in mind. The Texas Parks and Wildlife Department, for example, has a well-established Urban Wildlife Program with a staff of wildlife biologists who offer land-planning assistance to municipalities and property owners.

What sorts of planning decisions does the agency suggest to promote urban biodiversity? Richard Heilbrun, the program’s conservation outreach leader, points to San Antonio, where city planners asked for guidance on creating a network of recreational bike trails along local creeks. “The original plan called for trails that were 12 feet wide and brightly lighted at night,” says Heilbrun, “not very suitable for wildlife.” Instead of the manicured corridor originally proposed, San Antonio created bike trails that wind through diverse native plantings that provide habitat for hawks, owls and foxes (such as these kit foxes, below). “We’re located on the Central Flyway,” Heilbrun notes, “so hundreds of species of migratory songbirds also benefit from these river trails.”

Beyond helping cities make biodiversity a priority, the Urban Wildlife Program also engages residents in monitoring it. Heilbrun’s team works with citizen scientists who track the numbers and kinds of hummingbirds at their backyard feeders, for example. “Now we have much better data on where the different species are,” he says.



Managing for biodiversity is also a priority in Denver, Colorado, where visitors who fly into the area see one example as soon as they leave the airport. “A neglected piece of land adjacent to the main highway into town was an illegal dumping site, with trash, noxious weeds and a polluted creek,” says Scott Gilmore, deputy manager for Denver Parks and Recreation. Now the creek has been cleaned up, and Gilmore’s team also restored the native shortgrass prairie, improving habitat for raptors and deer.

Another Denver project targets Weir Gulch, a deep river valley that feeds into the South Platte River. “The gulches and rivers had been channelized,” Gilmore says, “but we’re returning them to a natural state with pools and riffles, and restoring native grasses and plants on the banks.” The area is adjacent to a neighborhood where 71 percent of the residents live in poverty. “We’re restoring riparian habitat right next to high-rise apartments, pawn shops and industrial parks,” says Gilmore, “creating spaces where kids can experience nature.”

What Nature Intended 
Better known for skyscrapers than wildlife, Chicago has developed Chicago Wilderness, an alliance of businesses and nonprofit groups working to restore green infrastructure and protect wildlife in the region. Abigail Derby Lewis of the city’s Field Museum is active in the alliance. “Our Climate Action Plan for Nature emphasizes restoring native biodiversity,” she says, pointing to trees as an example. Early in the 20th century, developers chose to plant native ash trees almost exclusively on many city streets, even though the original native forests were a rich mix of  species, including oaks. “Now we’re losing 30 percent of the urban forest canopy to the emerald ash borer,” Lewis says. “We need to make smarter decisions and choose replacements for the ash trees with the goal of increasing species diversity.”

To help urban planners across the country make biodiversity-oriented management decisions, the U.S. Forest Service has developed a convenient tool called i-Tree—modeling software that allows users to plug in different tree-planting scenarios and see how each would influence environmental factors such as water quality and air pollution. Suzannah Lerman, a Forest Service research fellow based at the University of Massachusetts–Amherst, is adding bird habitat models to the software so that planning for wildlife diversity can also be part of the process. “You’ll be able to ask, ‘What species of birds could that forest support?’” she says. “Do you need to add different tree species? Do you need more canopy cover? Do you need standing dead trees for cavity-nesters like chickadees?” The i-Tree program will help provide answers.

Lending Nature a Hand
Large green spaces like the 50-acre Thain Family Forest in the Bronx are key to protecting urban biodiversity.  But connecting small green spaces also helps. The National Wildlife Federation’s Garden for Wildlife™ program is challenging cities and towns to enlist their residents, businesses, municipal agencies and schools in efforts to transform properties into habitats that support native wildlife and plant species. “For native species to continue to thrive, we must make sure we provide appropriate space for them,” says NWF Naturalist David Mizejewski. “At the city scale, collective action really makes a difference.”

Cities across the nation are rising to the challenge. At this writing, 78 communities in 27 states have become NWF certified Community Wildlife Habitats®, and several more are on schedule to qualify for the program. Baltimore, for example, has launched a citywide effort called “B’More Wild” to achieve certification. Oak Crest, the city’s largest retirement community, is already a Certified Wildlife Habitat site with a pond, forest buffer zones and wildlife-friendly trees such as viburnum, wild cherry, oak and hickory on its 87 acres of grounds.

“Planned communities and homeowner associations can make a big difference for biodiversity because they coordinate the landscaping on multiple properties,” notes Lerman. In a study of how landscaping choices in Arizona backyards affected bird diversity, she found that some neighborhoods with homeowner associations chose a richer variety of plants—and supported more native wildlife—than did neighborhoods with no formal land-use rules.

“Many churches, synagogues and mosques also have extensive grounds,” adds Naomi Edelson, NWF director of state and federal partnerships, “and usually they’re planted with pretty ordinary stuff.” To enhance the biodiversity of these spaces, NWF is developing a new program called Sacred Grounds that will help places of worship create wildlife-friendly landscaping. “If more houses of worship considered biodiversity when choosing their plantings,” says Edelson, “it could really have an impact and also inspire congregants.”

Managing for biodiversity improves urban habitat for people, too. The famed 19th-century landscape architect Frederick Law Olmstead got it right when he called New York’s Central Park the “lungs of the city.” According to the Forest Service’s Urban Forest Ecosystem Research Unit, metropolitan forests inhale tons of carbon monoxide, sulfur dioxide, ozone and other gaseous pollutants, breaking them down into less-harmful compounds through photosynthesis.

City green spaces also provide vital ecosystem services. Constructed wetlands, rain gardens and green roofs can help manage storm-water runoff, reducing the risk of damaging floods while also helping protect drinking-water supplies by filtering pollutants from rainwater that washes over city streets. And the more biodiverse such constructions are, the better. “Sure, you could plant a bioswale with a monoculture of grass and it would do the job,” says NWF’s Director of Climate Change Adaptation Bruce Stein. “But if you cultivate a diverse collection of native plants, they’ll do a much better job managing storm water—while also providing food and forage for butterflies, bees, small mammals and birds.”

A Source of Serenity
Beyond these ecological services, green spaces provide measurable psychological benefits for humans. In one study, researchers in Great Britain found that people expressed greater feelings of well-being when they spent time in urban natural areas. The study subjects—ordinary city dwellers, not scientists capable of identifying plants at a glance—also reported feeling greater benefit from green spaces that contained more species, suggesting an intuitive appreciation for biodiversity.

As we reach the end of our walk in the Thain Family Forest, I can definitely see how green spaces make people happy—everyone we pass seems to be smiling. Aronson points out native wildflowers like jack-in-the-pulpit, spicebush and mayapple, a diversity of species that may be thriving here because the forest is protected from the destructive browsing of white-tailed deer—which are common in the suburbs but can’t cross city streets to get here. So not only do cities support biodiversity, Aronson notes, they can even be a refuge. 



How to Certify Your Community

As part of its ongoing efforts to provide habitat for native plants and wildlife and promote biodiversity in metropolitan areas, NWF’s Garden for Wildlife™ program certifies entire communities that provide appropriate sources of food, water, shelter and places to raise young. To learn more, visit www.nwf.org/community.

Certify Now

Pennsylvania writer Cynthia Berger is a regular contributor to this magazine.

Writer Lesley Evans Ogden is based in Vancouver, British Columbia.

More from National Wildlife magazine and NWF

Creating Bird-Friendly Urban Landscapes
Searching for Bird-Safe Windows
The Ultimate Urban Cats
When Carnivores Come Calling
NWF at Work: Urban Communities

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