Protecting Crops with Predators Instead of Poisons

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Protecting Crops with Predators Instead of Poisons
By Andy McGlashen
Environmental Health News | March 15th, 2018

The idea isn't new; the U.S. Department of Agriculture established an "economic ornithology" unit in the 1880s to study birds for pest control. But that body was disbanded in 1940, around the time synthetic pesticides like DDT were hitting the market and being hailed as wonders for controlling insects that spread disease and ruined crops.

By the 1960s, scientists were beginning to understand the serious ecological effects of those chemical compounds. Rachel Carson's landmark 1962 book Silent Springdetailed how DDT built up in birds and made their egg shells too thin to protect chicks, and its title raised the prospect of a future deprived of birdsong. A decade later, DDT was banned, and populations of raptors and other birds began to rebound.

But other pesticides hit the market. Currently more than one billion pounds of pesticides are used in the U.S. each year, and more than 5.6 billion pounds are used globally. Scientists increasingly point to potential health hazards of this widespread use—as certain pesticides have been linked to genetic changes, cancers, endocrine disruption, nerve disorders, mental health issues and reproductive problems.

In response, some food producers and researchers have grown more interested in the on-farm benefits birds can provide.

At this point, it's not clear how much pesticide use could be offset by partnering with natural predators, said Lindell, who describes beneficial birds as "one tool in the toolkit" of an integrated pest management approach.

However, she and others caution that if farmers are drawing in predators, they should avoid toxics to control pests, since the poisons can work their way up the food chain and kill birds and other animals. A study by the state of California found that three-quarters of raptors, bobcats, coyotes and other wildlife tested positive for rodenticides.

"People love to think that we've got to have poison in the toolbox, and we say you can't have both," said Lisa Owens Viani, director of Raptors Are the Solution, a California-based project of the nonprofit Earth Island Institute that works to stop rodenticide use. "We think it's unfair to put up an owl box and lure an owl to a place where there's poison being used. The bottom line: Do we want them to help us control rodents, or do we want to poison them?"

Owens Viani said that, at least in some cases, raptors alone are enough to control rodents. She pointed to a recent study by California's Ventura County Watershed Protection District, which works to control burrowing rodents that can degrade levees and dams. In findings published last December, the agency reported that levee sections where workers had installed perches to attract raptors had substantially less damage from ground squirrels than areas treated with rodenticides. The report called for replacing the poisons with raptors system-wide, noting that the county would save $7,500 a year for each mile of levee.

In another California study, barn owls essentially formed a colony at a research site after nest boxes were installed, with the population at one point reaching 102 owls on a 100-acre vineyard. The birds killed more than 30,000 rodents over the course of three breeding seasons, for a fraction of the cost of trapping or poisoning them, said lead researcher Mark Browning, a biologist formerly with the Pittsburgh Zoo who now owns the Barn Owl Box Company, which sells the nest boxes.

That suggests, at least in some situations, natural predators could make rodenticides unnecessary, he said.

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