New research shows that small habitats can add up to a big difference.
We love our lawns. In the United States more than 45 million acres—an area eight times the size of New Jersey—are carpeted with them. And we’re adding 500 square miles of turfgrass every year. Maintaining all that lawn is a huge undertaking and, for many, a source of personal pride. Annually, the average U.S. homeowner spends the equivalent of at least a full workweek pushing or driving a mower.
You could say the quest for perfect lawns—richly green, closely cropped, weedless, and insect-free—is almost as American as baseball. But this national preoccupation comes at a cost. Consider how many gallons of water and pounds of pesticides it takes to keep lawns lush. Depending on the conditions, a 25-by-40-foot yard can drink 10,000 gallons of water in a summer. Lawn care accounts for 70 million pounds of pesticides applied in the United States each year, 10 times more than even what is used in farming. The toxic runoff percolates into groundwater, threatening wildlife and human health.
What you get is a cookie-cutter landscape whether you’re in Palo Alto, Houston, Cincinnati, New York, or Phoenix. “All around the country you can find the same few species of grasses and foundation shrubs making up a national, undifferentiated residential landscape,” writes Pam Penick in her new book Lawn Gone!. “It’s like driving cross-country on the interstate and seeing the same four fast-food restaurants at every exit.”
And wherever green grass grows there was once habitat—a forest, prairie, wetland, or even a desert. Which is why many gardeners concerned about disappearing wilderness and wildlife declines are trying to grow the habitat back. With support from conservation groups like Audubon—or just for the love of it—they are digging up their yards and replacing the grass with trees, shrubs, and flowering plants that can again provide birds and other wildlife with food, clean water, shelter, and places to nest. Their spadework is unquestionably restoring varied and colorful homes where chickadees can sing and butterflies can flutter. But until recently few scientists could say for sure whether such efforts are having a meaningful impact on wildlife. Now they are finding proof that even small habitats can make a big difference.
In 2000, when Doug Tallamy bought 10 acres of former farmland near Oxford in southeastern Pennsylvania, one mile from the Maryland border, he wasn’t looking for a new research laboratory. He simply wanted a pleasant place to live with his wife, Cindy, and a reasonable commute to the University of Delaware, where he has now worked for 32 years as an entomology professor. The property, once mowed for hay, was overrun with unwelcome plants. “Autumn olive and oriental bittersweet, Japanese honeysuckle, bush honeysuckle, and multiflora rose—the whole gang was there,” he says.
The exotic plants (nearly all from Asia) overwhelmed most of the landscape. He bought a sturdy pair of hand loppers to cut through the thorns, including autumn olive’s thick, inch-long spikes. Eventually, he could take a walk without injury.
Soon he noticed something else disturbing. Most of those nonnative plants had little to no leaf damage from insects, unlike the indigenous maples, oaks, cherries, willows, and black gums, which were being eaten as usual. He was concerned. Was he witnessing a troubling consequence of the exotic plants that are spreading everywhere? If insects that spent millions of years eating native plants passed up a buffet of aliens—because they either couldn’t or wouldn’t eat them—did that mean areas dominated by foreign plants would support fewer insects? And if the insect populations plummeted, would birds starve?
Tallamy did an exhaustive search of the scientific literature to see whether he could find answers to those questions, but there was almost nothing. So he began studying how throngs of proliferating exotic plants are affecting insect populations and, therefore, the birds that eat them.
Healthy bird communities are inextricably linked to healthy insect populations. Ninety-six percent of terrestrial North American birds raise their young on insects. And not just any insects. Mostly caterpillars. Rich in fat and protein, caterpillars are essential for a bird trying to keep up with the demands of a hungry family. Consider the Carolina chickadee. It takes 390 to 570 caterpillars a day to feed a growing clutch of four to six chickadees in the 16 days from when they hatch to when they fledge from their nest. “That can be more than 9,000 caterpillars to make one batch of chickadees,” says Tallamy. “We know they’re not flying five miles down the road to forage. We know that almost all of a chickadee’s foraging happens within 50 meters [164 feet] of the nest. That’s why you need so many [caterpillars] in your yard.”
One of Tallamy’s studies examined the moth and butterfly larvae that develop on indigenous and exotic plants in the mid-Atlantic region (Virginia, Maryland, Delaware, Pennsylvania, New York, New Jersey, Connecticut, and Rhode Island), where you can find roughly 3,000 of the country’s total of 11,500 caterpillar species. From his findings he created a ranking system of regional trees and plants by the abundance and diversity of caterpillars they can host. First place on the top 20 list went to the oaks, which supported 534 species of caterpillars. Second place went to cherries and plums, which were home to 456; willows came in third, with 455.
The study confirmed Tallamy’s suspicions that gardeners could play a pivotal role in creating safe havens for wildlife. (An estimated 85 percent of invasive woody plants spreading through wild areas originally escaped from home gardens.) Thus he opens his landmark book, Bringing Nature Home, with a call to action: “For the first time in its history, gardening has taken on a role that transcends the needs of the gardener. Like it or not, gardeners have become important players in the management of our nation’s wildlife. It is now within the power of individual gardeners to do something that we all dream of doing: to make a difference. In this case, the ‘difference’ will be to the future of biodiversity, to the native plants and animals of North America and the ecosystems that sustain them.”
Many gardeners and botanists regard Tallamy’s book as the seminal source, and sales remain strong—the paperback is in its seventh printing. Throughout it, Tallamy avoids the term backyard habitat, because he says “it implies that these are so terrible we have to hide them in the backyard. When in fact the front yard is fair game. We’re not talking about creating ugly landscapes. A beautiful oak tree in your front yard is a highly functional plant there.”
Homeowners who landscape with native trees and plants such as oaks, goldenrods, asters, cherry trees, and sunflowers are planting bird food factories that ship caterpillars in bulk, and make regular deliveries of fruits and seeds that help fuel bird migrations over thousands of miles and multiple continents. “The plants in our yards are just as effective as the bird feeder you put up in wintertime,” Tallamy says, “because the plants are making the food that feeds the birds in the summertime.”
For a bird searching for a nice place to raise a family, the classic suburban yard—a tidy bed of grass, one or two shade trees, and a row of leafy foundation plantings imported from China—must be like a foreclosed fixer-upper in a bad neighborhood. The accommodations are spare and all the local restaurants are dives.
The nice neighborhoods, on the other hand, where native plants abound, offer all the perks of a Park Avenue suite with a stocked pantry and a view. There is abundant food, places to nest, and a brilliant stage upon which a bird can sing without competing against the din of a lawn mower.
One of Tallamy’s undergraduate students, Karin Burghardt, compared two such types of landscapes in southeastern Pennsylvania. One property in each of six pairs had a higher proportion of native plants, and the other was more typically suburban, with an indigenous tree canopy casting shadows on lawns fringed by alien ornamental bushes and ground covers like pachysandra.
Not surprisingly Burghardt found a greater diversity and abundance of birds and caterpillars in the yards filled with naturally occurring plants. But one finding blew the researchers away. Birds of conservation concern in the area where the study was done—wood thrushes, eastern towhees, veeries, and scarlet tanagers—were eight times more abundant and significantly more diverse on those parcels. “There was a big jump in their ability to use these properties,” says Tallamy.
During the three months it took Burghardt to gather data, 125 square miles of lawn grew across the country, even in areas where you wouldn’t expect to find grass growing. In Phoenix, Arizona, where temperatures can hit 120 degrees Fahrenheit, the popular garden “oasis” is a mix of turf, subtropical palm trees, and a scattering of desert-adapted plants. Susannah Lerman, a researcher from the University of Massachusetts-Amherst, traveled there to examine the difference between how birds use the “oasis” compared to grounds brimming with native desert plants (a gardening style known as xeriscaping; see “Hollywood Native.”).
The well-watered oasis yards were ruled by grackles, house sparrows, and European starlings—everyday birds that wouldn’t normally survive in such a hot and dry place. “You’re not going to see those species naturally in the desert because they can’t make it without water,” she says. “But as soon as you add water—boom.”
On the properties most closely resembling the arid desert surroundings, she found Gila woodpeckers nesting in saguaro cactuses, Anna’s hummingbirds sipping nectar from mesquite, and curve-billed thrashers nesting in cholla cactuses. She also discovered that the birds frequenting those xeriscaped properties were staying longer and eating until they were full. “They didn’t have to keep moving around, which takes a lot of energy,” she says. “They could stay in one patch and do all of their activities. If you’re a bird that doesn’t have to fly from yard to yard desperately trying to find food, you can go off and do other important things, like attracting a mate or feeding your young.”
Lerman worries about one potential hazard of creating a bird retreat in a desert of grass and pavement. In the right set of circumstances it could become a Bates Motel. “We have to be really careful that when we do create these habitats we don’t create ecological traps.” (This refers to the inadvertent bait and switch that can happen when wildlife is drawn to an area that ultimately jeopardizes its safety.) “If you create a wildlife habitat, and then you have a cat outside, it’s completely unproductive. You’re attracting all these birds to your yard with beautiful plants, and your cat is waiting to kill them.”
It doesn’t have to be your cat either. It could be a neighbor’s or a feral one. In fact, a recent study by scientists at the Smithsonian Conservation Biology Institute reported that between 1.4 billion and 3.7 billion birds are killed each year by cats roaming outdoors. “This is a huge and complicated issue,” Lerman says, “because you can’t control other people’s behavior.”
While cutting-edge research is expanding scientists’ understanding of how people can support birds and other wildlife—one garden, schoolyard, and urban park at a time—there is still a lot to learn. “Prior to this research, it was largely suspected that backyard habitats could be helpful in providing sanctuary to birds during nesting and migration,” says Steve Kress, Audubon’s vice president for bird conservation and author of The Audubon Society Guide to Attracting Birds. “Their research gives us solid information that shows how important the native plants are.”
But he emphasizes that selecting plants that host the insects birds eat is only part of the equation. Fruiting plants and seeds fuel birds during migration, and are thus equally essential in any habitat. “Of course, plants should also be selected for other features than food, such as shelter during extreme weather and usefulness for nesting structure. Just as some plants sustain diverse caterpillar populations, others provide good options for nesting structure and safety from predators.”
Nest boxes hung on posts or standing trees are another key feature, he says, because people tend to remove downed trees and other structures with cavities that birds would use naturally. In addition, birds need sitting perches where they can keep an eye out for predators; a place to get out of the sun on a hot day or to weather a winter storm; water for drinking and bathing; and even some thorny shrubs like hawthorns that can provide a fortress against prowling animals, including cats.
At the same time scientists are taking a hard look at nonnative invasive species that provide birds with food but also harm the ecosystem. Porcelainberry is firmly on the National Park Service’s “least wanted list” for its habit of forcefully twining through woodlands and smothering native plants. But apparently the birds aren’t too picky. “[They] eat porcelainberries up the wazoo,” says Michelle Frankel, a conservation biologist who is leading Audubon’s Bird-Friendly Communities initiative in the Atlantic Flyway. Some people think: Why make such a fuss. Just leave it. But Frankel says you have to also consider the plants that porcelainberry displaces. What’s more, not all plants are created equal. A recent study revealed that the highest fat content and energy densities in fruits that migrant birds ate at two field sites in Rochester, New York, came from native shrubs—not the aliens. The birds were choosing the higher-octane fuel and eating it more voraciously.
More and more, citizen science projects continue to deepen our understanding. Two such programs were launched this spring. “These initiatives are designed to look more closely at bird and plant associations and answer some of the questions, particularly having to do with backyard habitats,” says Frankel.
YardMap is a Cornell Laboratory of Ornithology project that encourages people to gather data about the habitats that they are most familiar with—their yard, their favorite birding spot, a schoolyard, even a cemetery—to provide insights about how they can aid wildlife. The program is like Google Earth, allowing users to zoom in on their place and mark the types of plants that exist there. “It’s connected to eBird [a real-time online checklist program that collects and broadcasts bird data], so they can also keep track of the birds they see,” says Frankel. “It’s a very cool tool.”
She says that the program is being promoted to Audubon chapters around the country, and the schools, neighborhood groups, and municipalities receiving mini-grants to create “Urban Oases” demonstration habitats will be asked to track their sites with YardMap.
The second program, called Hummingbirds at Home (www.hummingbirdsathome.org), joins Audubon’s citizen science programs, such as the Christmas Bird Count and the Great Backyard Bird Count, by enlisting people to log observations of hummingbirds on flowers and note blooming patterns. Several recent studies indicate that the arrival of hummingbirds on their foraging grounds is out of sync with food availability and flower pollination. “The Hummingbirds at Home program aims to gain insights into what’s going on, and how people can help,” says Audubon chief scientist Gary Langham.
There is plenty of evidence to show that anyone can play a vital role in preserving bird habitats, says Tallamy, who even goes as far as to call it a moral imperative. “Our success is up to each one of us individually,” he writes in Bringing Nature Home. “We can each make a measurable difference almost immediately by planting a native nearby. As gardeners and stewards of our land, we have never been so empowered—and the ecological stakes have never been so high.”
Shovel Ready: Transforming Your Yard
- Get started by signing Audubon’s Healthy Yard Pledge to promote bird-friendly communities. It aims to remove invasive exotic plants; plant native species; reduce pesticide use; conserve water; protect water quality; and support birds and other wildlife. Visit audm.ag/HYPledge.
- Begin small and have a plan. “Someone always comes up [after a talk] and says, ‘I’m going to run home and rip out all my lawn,’ ” says Doug Tallamy, author of the renowned gardening book Bringing Nature Home. “That is not my recommendation. If you take something out, be ready to replace it.” He suggests an easier pace. “This can be a hobby. You don’t have to do it all at once.” Or, for instant results, hire someone to do the work. If you already pay to have your lawn cut and cared for, you might consider putting at least part of that budget toward managing your yard in a way that’s more beneficial to birds.
- Convert the salespeople at your nursery. If you go to one with the name of a native plant that you want to buy, they will likely take you to the closest thing in stock. “What you say to them is, ‘That’s not what I want. Can you get this for me?’ And if they can’t, you walk away,” says Tallamy. “If they hear that enough they’ll start carrying this stuff.” (Find resources that can help you locate plants native to your region at audubonmagazine.org.)
- Try to avoid cultivars of the native plants you’re buying. When the horticultural industry tweaks a plant’s features (for instance, its color or petal size and shape), the plants may become less desirable or even incompatible with the insects that evolved to eat them.
- Shun the misconception that gardens brimming with native plants look weedy. “If you go to the fine gardens of Europe, many of the plants they display are from North America,” says Tallamy. “So this notion that just because a plant grows down the street, it can’t be used formally is just an urban legend.” For some domestic inspiration, Tallamy points to a new 3.5-acre native plant exhibit at the New York Botanical Garden that is both beautiful and beneficial for wildlife in one of the world’s most crowded cities.
- There’s power in numbers. Enlist your neighbors and wider community to help incorporate bird-friendly plantings in yards, parks, workplaces, schoolyards, and other public areas. Join a growing army of citizen scientists collecting data about how birds can coexist with us and become part of Audubon’s Hummingbirds at Home program. Visit audubon.org/citizenscience, where you can also download the mobile app.
- This winter participate in the Christmas Bird Count (birds.audubon.org/christmas-bird-count) and the Great Backyard Bird Count, two ongoing citizen science programs that help track long-term bird population trends.
- Register your plot of habitat at YardMap and document its value to birds as you make improvements.
- Hang out at home. Half the nation’s lawn equals about 20 million acres—roughly the collective size of 15 national parks, including Denali, Yellowstone, Yosemite, Great Smoky Mountains, and The Badlands. “We have to get rid of the notion that nature is something you must drive to,” Tallamy insists. “That’s why people go to national parks, to connect with nature. You can do that right at home—every time we look out the window or go outside.”