What Do Birds Do for Us?
Some might not realize the tangible value of birds, but it would be foolish to underestimate how tough life would be without them.
Of course, none of these studies measures the personal benefits that watching a warbler can bring. Studies have shown that spending time in nature improves both cognition and mental health. "Birding is such a gateway to nature," says Ohio's Kimberly Kaufman. "It gets people outside--away from the computer, away from the television." It exposes them to fresh air and lifts their spirits. "We've been using the phrase ecotherapy, " she says. "Let's face it: We can all use more joy in our lives."
Perhaps the least sexy service birds provide is eating dead bodies. "We've got an enormous amount of roadkill produced on our highways in the United States," says Travis DeVault, a research wildlife biologist with the U.S. Department of Agriculture. "I don't think anyone knows what that would look like if vultures weren't around to clean up a big portion." Though scientists have long valued scavenging birds for their sanitation services, he says, "it's pretty recently that we've begun to discover how that translates into human health."
Some of that discovery has come the hard way--from a natural experiment playing out today in South Asia. Vultures are particularly valuable in India because Hinduism prohibits the slaughter and consumption of cows. The livestock, therefore, die naturally, in the open. "We don't have an organized carcass-disposal system," says Vibhu Prakash, principal scientist at the Bombay Natural History Society. "After skinning, vultures would come, and within half an hour they would finish everything that is perishable from a carcass. Then we have people who collect the bones, so there will be no mess around and no stench."
Starting in the 1990s the populations of oriental white-backed, long-billed, and slender-billed vultures began to crash. Researchers noticed the birds' necks drooping in the wild, a sign of debilitating weakness. Within a month, they would be dead. Today their numbers have been reduced by 99 percent-- 99.9 percent for oriental white-backed vultures. Scientists traced the cause to an anti-inflammatory medicine called diclofenac, which is used as a painkiller for aging cows but also triggers fatal kidney disease in old-world vultures.
In 2006, after a bird-friendly alternative drug was identified, India banned the veterinary use of diclofenac. While some pharmaceutical companies have cooperated, others continue to sell the human formulation in multiple-use vials large enough to medicate a cow. They have refused pleas by conservationists to sell the drug only in small vials appropriate for human doses. "For the drug companies, profit is the main consideration," says Prakash. "They will not stop manufacturing multi-dose vials voluntarily."
Without vultures around, feral dogs have taken over carcass disposal. Massive packs roam India's trash dumps, looking for piles of dead cattle to eat. With this growing canine population comes more fatal dog attacks, as well as rabies from bites. (India has the world's highest human rabies rate.) Economist Anil Markandya has estimated almost 40 million additional dog bites in India between 1992 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.
South Asia's vulture story offers the most dramatic example of how birds keep us healthy. But non-scavenging species contribute, too. While ducks have been implicated in the spread of influenza, in 1914 Pennsylvania's health commissioner, Samuel Dixon, declared that "the duck is one of the greatest known enemies of the mosquito, and therefore of yellow fever and malaria." Dixon ran an experiment involving two ponds--one stocked with mallards and the other with goldfish--and discovered that the ducks ate mosquito larvae far more "ravenously" than the fish did.
In the high mountains of the American West, there's a tree called the whitebark pine that both humans and other animals have come to rely on. Its large seeds feed grizzlies and black bears. Whitebark pine communities provide habitat for deer, elk, and raptors. And because the pines grow all the way up to the treeline, they are effective at protecting drinking-water supplies. "The mountains are the water towers," says Diana Tomback, a professor of integrative biology at the University of Colorado-Denver. The trees' roots hold the soil in place, preventing erosion. Their presence reduces the danger of avalanche. And their canopy shades the snowpack, ensuring a protracted melt rather than a sudden springtime flush.
The tree's seeds are dispersed by just one bird: 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. "What would happen if we didn't have the Clark's nutcracker?" Tomback asks. "In the case of whitebark pine, it is unlikely that it could sustain itself."
The value of the nutcracker is coming into sharper focus now that the tree is in danger. A fungal disease called blister rust and the growing menace posed by the mountain pine beetle (in part because of global warming) have delivered what Tomback calls a "one-two punch." In some areas, she says, "whitebark pine ecosystems are verging on nonfunctional."