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1. They provide pest control.

Modern history is filled with stories of birds saving potato fields, fruit orchards, and cranberry bogs from insect devastation. Now researchers are studying the phenomenon more formally, trying to quantify birds' value as living pest controllers.

Consider the case of the coffee berry borer. These tiny insects invade individual coffee berries and spend almost their entire lives inside, making those beans unsellable. There are no safe pesticides that kill the insects, and attempts to control them with parasitic wasps have shown, at best, limited success.

But black-throated blue warblers, American redstarts, and other birds feast on the borers when the insects are first drilling into the berries. A researcher at one site in Jamaica's Blue Mountains calculated the birds' pest-control value at $125 per acre, or nearly one-eighth of the total crop value of $1,044 per acre.

In the Netherlands insect-eating birds protect apple orchards, and in Missouri's Ozark Mountains they safeguard white oaks, whose lumber is highly sought by furniture makers. Birds even reduce pests at organic wineries.

2. They're money makers.

Birds stimulate economies just by being the beautiful, fascinating creatures they are. In an economic analysis released in 2009, the U.S. Fish and Wildlife Service calculated that, based on a 2006 survey, birders spend $12 billion annually on travel and an additional $24 billion on equipment including binoculars, camping gear, and nest boxes. That money ripples out, generating $82 billion in economic output, employing 671,000 people, and enriching state and federal governments by $10 billion.

You need only visit Ohio's Maggee Marsh to see that ripple effect in action. This 2,000-acre wildlife refuge on Lake Erie is a stopover for neotropical migrants, which rest and refuel before crossing the lake. With such avian abundance, the marsh attracts more than 100,000 birders a year. One researcher calculated that in 2011 Magee Marsh and five other Lake Erie birdwatching areas in Ohio collectively generated $26 million in spending and created 283 jobs.

3. They clean up.

Perhaps the least sexy service birds provide is eating dead bodies. They clean up enormous amounts of roadkill all over the world. Unfortunately, vulture populations everywhere have suffered major declines. In many cases, the cause can be traced to indirect poisonings that are the result of drugs given to the animals the vultures feed on. When vulture numbers plunged in India, feral dogs took over carcass disposal. This led to a growing canine population, which meant more fatal dog attacks, as well as an increase in rabies and bites.

Economist Anil Markandya estimates that there have been almost 40 million additional dog bites in India between 2002 and 2006, resulting in about 48,000 extra deaths. He calculates that the vulture-dog connection alone produced human health costs totaling $34 billion over 14 years.

4. They spread seeds.

In the high mountains of the American West, the future of a tree called the whitebark pine hangs in the beak of a particular bird. The tree's seeds are dispersed only by the Clark's nutcracker, a black-and-white-winged cousin to the crow. The nutcracker's long, sturdy bill opens the pinecones to pluck out the seeds, which it eats or stores inside its throat. It then buries the uneaten seeds at the depth and location that the trees often need to reproduce. Without the nutcracker, it's unlikely that the whitebark pine could sustain itself.

Researchers with the U.S. Forest Service have done some experiments that help quantify the value of the nutcracker's dispersal service. They figure its worth at between $800 and $1,000 per acre, based on what it would cost to plant the pines by hand. Multiply that by about 14.3 million acres of whitebark pine forest, and you get savings of more than $11 billion in the United States alone.

5. They announce danger.

Most of us are familiar with Silent Spring, Rachel Carson's 1962 book, which chronicled the lethal effects of the DDT. Carson's robins—along with bald eagles exposed to the pesticides—signaled to many Americans that birds could serve as "winged sentinels" of environmental degradation. More than 50 years later scientists routinely use birds to gauge the health of ecosystems—and not just for purely biological reasons.

Tree swallows are providing insight on the impact of a wide range of PCBs in the Great Lakes and Hudson River, pulp-mill effluent in western Canada, petroleum in Wyoming's North Platte River, and metals in New Jersey. Likewise, scientists have been monitoring the health of common loons in New York's Adirondack Park to understand the impact of atmospheric mercury from coal-burning power plants and incinerators. By measuring the loons' breeding success and correlating it to mercury contamination, scientists have been able to provide evidence for the need to stringently regulate mercury and acidic emissions on national and global scales.

6. They pollinate.

Pollination is the recognized realm of bees, bugs, and butterflies. But more than 900 bird species worldwide pollinate, too, and their sophisticated sense of geography suits them well to the task. The durian munjit, a wild fruit that is collected and eaten in northern Borneo, relies exclusively on spiderhunters, members of the sunbird family.

A passerine called the Canarian chiffchaff pollinates the Canary bell-flower, an ornamental plant with edible fruit that grows on Spain's Canary Islands. (It was cultivated in the royal garden of England's Hampton Court Palace as early as 1696.) And when the cold weather keeps insects away, China's winter-flowering loquat tree reproduces with the help of two passerines, the light-vented bulbul and the Japanese white-eye. The loquat's fruit is eaten in many forms and used medicinally.

7. They help farmers.

After California farmers harvest their rice crops, they need to get rid of the leftover rice straw. Burning it is cheap, but it pollutes and is therefore illegal. An alternative, tilling the straw into the soil, is expensive.

Fortunately, farmers can enlist help from wintering waterfowl that travel along the Pacific Flyway. By foraging for leftover grain, weeds, and bugs in flooded rice fields, mallards and other birds help decompose the straw. This reduces the need to till the fields, providing considerable savings to growers, concluded a 2000 study from the University of California-Davis. Farmers would be well advised, the report noted, to flood their fields and create wetlands for these avian wayfarers.

8. They poop.

Seabird guano—rich in nitrogen, phosphorus, and other nutrients—provides an important source of fertilizer and income to many people living near seabird colonies. This has been true for centuries: Guano was considered essential to the Incas' agriculture, "upon which their civilization was based," wrote Edward How Forbush in 1922. Two years earlier ornithologist Robert Cushman Murphy determined that the best Peruvian guano was 33 times as effective as barnyard manure based on its nitrogen content.

Unfortunately, guano production is one of the most threatened avian ecosystem services, due to the rapid decline of seabirds worldwide, say scientists. Among the culprits are fishing longlines, which lure and then drown such birds as black-browed albatrosses.

9. They are heroes.

Birds possess skills that historically made them useful to militaries. During World War I pheasants detected incoming hostile aircraft at long distances and "gave the alarm by their insistent cries," says one account; canaries, of course, offered early warnings of poison gas; gulls followed submarines in search of garbage. Carrier pigeons successfully navigated through shellfire (and past bullets aimed at them). They carried messages that helped the Allies capture German submarines, and that saved the crews of downed seaplanes and a sunken mine sweeper.

10. They just are.

We have all been transported by simply watching a flying bird. We have been lifted out of ourselves; we have felt our hearts race when the wings flash by.

Every one of us has seen what really matters—seen it in the blistering stoop of a peregrine, heard it in the richly harmonic dawn song of a thrush, caught its essence in the slow undulations of white pelicans against a blue sky.

And we've realized that for those moments, we were privileged to experience something beyond ourselves—that older, greater, glorious world that a wild bird inhabits, and which through its very existence embodies and makes vivid to us.

Adapted from "," by Barry Yeoman, and "," by Scott Weidensaul, in ±¬ÁϹ«Éç magazine's special "Why Birds Matter" issue (March-April 2013).