Increasingly each year, humans foraging in American supermarkets select organically grown food. Not so with wild songbirds searching for sustenance in the gardens of England.
Given a choice between organically and conventionally grown wheat, they opt for the conventional stuff — which is higher in protein — 55 to 60% of the time, a study has found.
The findings, which were published in the Journal of the Science of Food and Agriculture on Tuesday, raise yet again the question of which is healthier: organic or conventional food.
The research team, based at the school of biology at Newcastle University in England, didn't expect the birds to prefer conventionally grown wheat, said lead researcher Ailsa McKenzie. Earlier lab studies had reported that hens and rats preferred organically grown beetroot and wheat over conventionally grown.
But the problem with earlier preference studies, said McKenzie, is that none tested animals for longer than seven days, which meant that the animals did not have time to establish a preference.
"Birds learn," she said. "They need to associate what they're eating with where it is to learn a preference."
In the Newcastle study, researchers positioned two feeders — one stocked with organic wheat and another with conventionally grown wheat — in 36 English gardens. Then over a period of six weeks in 2008, they measured how much wheat birds ate by gauging every two days how much food was consumed from each feeder.
The scientists conducted a second test in early 2009, this time studying 15 gardens over eight weeks. They also tested preferences among canaries in the laboratory.
All three trials found a preference for the conventionally grown food. In the 2008 trial, for example, the birds consumed 58,954 grams of wheat, 45% of it organic and 55% conventional.
The higher protein content of the conventional wheat — about 10% greater than the organic wheat's — "most likely" accounted for the birds' liking it better, the scientists wrote.
Conventionally grown crops are usually treated with fertilizers that deliver higher levels of nitrogen to plants than organic fertilizers do, in a form that can be processed more quickly. Plants use nitrogen to produce protein.
What the findings mean for humans is unclear.
"Our results suggest that the current dogma that organic food is preferred to conventional food may not always be true, which is of considerable importance for consumer perceptions of organically grown food," the report concludes.
Advocates of organic farming beg to differ.
"For a team of scientists to extrapolate from a modest difference in what birds selected to make a statement that consumer perception should change is ludicrous," said Charles Benbrook, chief scientist at the Organic Center, a research organization in Boulder, Colo., that promotes "the conversion of agriculture to organic methods," according to its website.
Benbrook said most consumers say they buy organic produce to avoid pesticides and because they prefer the taste. U.S. sales of organic food were $24.8 billion in 2009, according to the Organic Trade Assn., an industry group in Greenfield, Mass.
Benbrook said that although conventionally grown crops are higher in protein, organic foods are higher in vitamin C and antioxidants — health-promoting nutrients that, unlike protein, are lacking in the Western diet.
"This is a silly study," he said. "It suggests to me that they're grasping at straws to say something negative about organic food."
But Robert Goldberg, a professor at UCLA's department of molecular, cell and developmental biology, said there was no scientific evidence that organic food is better than food grown conventionally.
"It's one of the most popular non-scientifically supported myths out there. …It costs consumers who purchase organic food a lot of extra money for no nutritional benefit, or any other benefit," he wrote in an e-mail.
McKenzie agreed that it would be hard to extrapolate from the study to human preferences and agreed that people buy organic for many different reasons.
"Just because the birds preferred conventional food doesn't mean it's better for them," she said. But at least the study "will make people think."
Unlike English finches and sparrows, she has nothing against organic produce, she added. "I don't have an agenda. I eat organic food."