Like the hum of bees and the rising-and-falling flight of monarch butterflies, the dramatic swoop of swallows is one of the common, comforting features of a rural landscape. Along with other farmland bird species, such as tree sparrows and starlings, swallows are part of the rich ecology that exists in agricultural areas. But like bees and butterflies, their populations are being affected by the use of chemical pesticides on the fields they call home.
A study published Wednesday in the journal Nature suggests that a dramatic drop in populations of farmland birds in the Netherlands is likely tied to the use of neonicotinoids—the same class of systemic pesticide implicated in honeybee population declines. The peer-reviewed study found that concentrations of imidacloprid, a type of neonic, of more than 20 nanograms per liter in surface water brought about a population decline of 3.5 percent annually. The researchers, led by Hans de Kroon of Radboud University, date the beginning of the bird declines to the mid-1990s, when neonics were first introduced.
David Goulson, a professor at the University of Sussex who was not involved with the study, tells The Guardian that the results ring true: “The simplest, most obvious explanation is that highly toxic substances that kill insects lead to declines in things that eat insects.”
Just as neonics kill insects, such as bees, when they consume parts of plants that are treated with the systemic pesticide—which is applied to the seed and remains present throughout the plant for an extended period of time—the neurotoxins are passed along to other species too. The Nature study found that at least 95 percent of what’s applied to crops ends up in the surrounding environment. And similar to the loss of honeybees, which could have a catastrophic impact on agriculture, declining bird populations are bad news for farmers too. Insectivorous birds—such as swallows—one of the species most affected in Holland, are like death on wings for the same pests the chemicals are being used to eradicate.
Barn swallows, for example, love to eat aphids, the scourge of vegetable farmers. Instead of making these and other pests toxic to the birds—killing or weakening all parts of the ecosystem—some farmers who practice integrated pest management take advantage of the birds as one tool in a broad-ranging fight against pests. A study published in PLOS One in 2011 found that after encouraging Western bluebird populations in California vineyards, birds in areas near nests ate 3.5 times more larvae of beet armyworms—a pest—than those in control plots.
Another 2011 study, published in the journal Environmental Toxicology and Chemistry, found that birds that feed on insects were more dramatically affected by changes in pest management than species who eat seeds and grains. The researchers, who focused on apple orchards in southeastern France, observed that overall populations and species diversity “were highest in organic orchards and lowest in conventional orchards during the three study years.”
News that starlings were one of the species most adversely affected by neonics in the new study will surely be met with glee by some American farmers. The European species was introduced in North America in the 1890s, and the population has since boomed. Considered an invasive species, the birds have been blamed for contaminating grain harvests with their droppings and spreading infectious diseases across livestock populations. There’s a wealth of starling-killing footage on YouTube.
But what may be considered “good” news in the eyes of some is yet another sign that Rachel Carson’s promise of a silent spring could still become reality. While much of the prairieland and grassland habitat that North American bird species used to call home has been plowed under, swallows and others have adapted to the farmland that replaced them. Rather than further marginalizing them with deadly chemicals, farmers should embrace these species as the highly evolved insect killers they are.