WASHINGTON - Using crops genetically engineered to resist weedkillers might harm birds - not because the genetic changes are harmful but because killing weeds means less food for birds, researchers said yesterday.
Some farms where such crops are used could see a 90 percent drop in the number of weeds - a boon to farmers but bad news for hungry birds, Andrew Watkinson of the University of East Anglia in Norwich, England, said.
Watkinson and colleagues used a computer model to predict the effects that planting a weedkiller-resistant sugar beet would have on a weed known as lamb's quarters or fat hen (its scientific name is Chenopodium album), whose seeds are a major food source for skylarks.
"We predict that weed populations might be reduced to low levels or practically eradicated, depending on the exact form of management," they wrote in their report, published in the journal Science.
"Consequent effects on the local use of fields by birds might be severe, because such reductions represent a major loss of food resources."
They said the effects on overall bird populations would depend on whether a few large farms used the genetically modified (GM) crops in just a few places, or if such crops were planted by many different farmers.
"These results probably apply widely to other crops, weeds, and seed-eating birds," Watkinson told Science.
But he stressed the results would be seen as a result of any weed management practice. It is just that using GM crops is a particularly effective way to get rid of weeds, he said.
Watkinson said bird populations in Britain have fallen by up to 90 percent in the last 25 years.
"It seems likely that the widespread introduction of herbicide-tolerant crops will result in further declines for many farmland birds unless other mitigating measures are taken," he said.
Monsanto Corp., which makes the Round-Up Ready soybean genetically modified to resist its herbicide of the same name, was quick to issue a response to the study.
"It is important to understand that this is not an issue of biotechnology," the company, a division of Pharmacia Corp., said in a statement.
"It is an issue of weed control, whether through biotechnology or other methods. This mathematical model, and any conclusions drawn from it, must be viewed with caution because it does not reflect real farming conditions."
But Watkinson had pointed out that using a computer model saved having to wait for years of field studies.
One argument made in favour of GM crops is that they can allow farmers to use less weedkiller than they normally would, because they can kill off weeds with one big dose while leaving crops undamaged.
"Data from other scientists who have conducted field studies on herbicide-tolerant sugar beets has shown that herbicide-tolerant plants allow farmers to maintain weeds longer in sugar beet fields, which could offer greater resources at a time of year when food for birds is scarce," Monsanto argued.
"Agricultural practices that improve the yield per acre actually prevent additional land from coming under cultivation, preserving the best wildlife environments in their natural state and protecting indigenous habitats for birds and other wildlife."
GM crops have been attacked by environmental groups, which have cited studies that suggest that Monarch butterflies can be harmed by pollen from GM plants.
Most recently, Iowa State University researchers said Monarch butterfly caterpillars were seven times more likely to die when they ate milkweed plants carrying pollen from Bt corn, which produces a pestkilling protein taken from bacteria known as Bacillus thuringiensis.
Other researchers have attacked this and similar studies, saying they do not reflect real-world conditions.
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Last Updated on 9/4/00