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.
In response, the U.S. Forest Service has been growing rust-resistant whitebark pine seedlings to plant by hand. This is labor-intensive work: Specially trained climbers must ascend into the canopy twice, first to place animal-proof cages around the cones (which need water and nutrients from their parent trees) and later to harvest the cones. In nature the seeds would germinate over two years, but the forest service speeds the process by specially treating the seeds before they are sown for germination. Figuring out the cost of this process has allowed Tomback to calculate the value of the nutcrackers' dispersal services: between about $800 and $1,000 per acre, based on what it would cost to do the hand planting. Multiply that by about 14.3 million acres of whitebark pine forest, and that's more than $11 billion in the United States alone.
Throughout the world, birds are essential seed dispersers for plants that provide us with food, medicine, timber, and recreation. Among their qualifications: They travel long distances. They assist germination when they eat fruit by removing the pulp and scratching the seed coat. Sometimes their interests coincide perfectly with a tree's.
That's the case in Costa Rica, where male three-wattled bellbirds show off to females from song perches at the edges of canopy gaps. "They're trying to be conspicuous," says Dan Wenny, an ornithologist at Iowa's Loras College. "So they often pick areas that are more open." The bellbirds consume fruit from trees in the avocado family, which are highly prized for their timber. The birds frequently deposit those seeds in the sunny areas below their perches. "It turns out that being dispersed into a gap is an advantage," says Wenny. "There's a lower probability of getting infected by fungal pathogens."
Many of us have read Rachel Carson's 1962 book Silent Spring, which chronicled the lethal effects of the insecticide DDT. While Carson, a biologist, documented the havoc wreaked throughout the food chain, her book is best remembered for its account of how the fight against Dutch elm disease poisoned entire populations of robins as well as 90 other bird species. Carson's robins--along with the thinning egg shells of American bald eagles exposed to 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. Birds often meet the technical criteria, such as sensitivity to environmental changes. "But there's also this practical reason that if we're going to translate science into public action, it needs to be something we care about," says biologist John McCarty from the University of Nebraska-Omaha. Another practicality: Humans have recorded bird populations for generations. "Because people care about birds, we have a lot of data out there"--the North American Breeding Bird Survey and National Audubon's Christmas Bird Count are among the best known --"that we can use to try to evaluate ongoing changes without having to start a whole new program," McCarty says.
McCarty is among the researchers who have used tree swallows to study the impact of a wide range of toxins: PCBs in the Great Lakes and Hudson River, pulp-mill effluent in Western Canada, petroleum in Wyoming's North Platte River, metals in New Jersey. Their work has shown that contaminants that land in aquatic sediment don't remain there; they work their way up the terrestrial chain.
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. A 2012 report by the Maine-based Biodiversity Research Institute (BRI) calls the birds "excellent sentinels of threats impacting aquatic ecosystems. They live more than 20 years, are at the top of the food web, and are very territorial." By measuring the loons' breeding success and correlating it to mercury contamination, the BRI has been able to provide "evidence for the need to stringently regulate mercury and acidic emissions on national and global scales."
Scientists use bird abundance to measure everything from wetlands health to radioactive contamination. Some of the most innovative work uses birds to study climate change. On the Crozet Archipelago in the southern Indian Ocean, zoologist Lewis Halsey has placed heart monitors on king penguins to measure how much energy they expend while foraging for fish. Halsey, who now lectures at London's University of Roehampton, says energy levels might have to increase if climate change or overfishing makes food more scarce.
And at Oregon State University, researchers use microphones to mechanically monitor bird songs in the western Cascade Mountains during (and before) the breeding season. "The minute the bird arrives from its wintering grounds, you know when it showed up," says Matt Betts, an associate professor of landscape ecology. "Then, if you start comparing those data across years, you can get some idea of how arrival times shifted. As the climate starts warming, are we seeing birds arriving earlier? This is being reported in some studies, but our effort would be to do this in an automated way," and thus collect more data than manual counts possibly could. Betts is now working with computer scientists on his campus to create a program that identifies species by call, even in noisy forests.