Creating a Bird-Friendly Yard
New research shows that small habitats can add up to a big difference.
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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."