For example, more than 13 percent of the Chernobyl birds had partial albinism—tufts of white feathers—compared to levels of around 4 percent in the control birds.
"Abnormal features [like albinism] are extremely rare in nature," Møller said.
Recapturing the same birds year after year showed that birds with abnormalities were four times less likely to survive and that breeding success was reduced by over 50 percent.
The findings support the team's theory that even the low levels of radiation around Chernobyl are enough to cause the higher than average rates of abnormalities and birth defects reported in humans living in the region.
"Based on the bird data, we think there is likely to be a plethora of human ailments associated with the Chernobyl radiation," said Mousseau, who is also carrying out a health study on children living in the Chernobyl region.
Radiation vs. Stress
The team's theory directly contradicts a 2005 report prepared by the Chernobyl Forum, which is led by the International Atomic Energy Agency (IAEA) and the World Health Organization (WHO).
The forum had concluded that social stress and the collapse of agriculture after communism was overthrown in 1990 were the most significant causes of poor health in the region.
"We found that there was a lot of anxiety amongst the population," said Burton Bennett, a retired radiation specialist who chaired the Chernobyl Forum.
"In general the doses of radiation that people were exposed to were low—comparable to background levels over the course of ten years or so."
Bennett is unconvinced by Møller and colleague's findings.
"It takes very high levels of radiation to cause abnormalities, and I really doubt that this study can be substantiated," he said.
According to the Chernobyl Forum report, about 6.6 million people were exposed to high doses of radiation and 56 people were directly killed by the disaster.
The report estimated that as many as 5,000 people may die from some form of cancer related to the radiation.
Møller and colleagues think that the health impact could be much worse.
Keith Baverstock, an environmental scientist at the University of Kuopio in Finland and co-author of a 2001 United Nations report on human health around Chernobyl, agrees that the results of the bird study are worrying.
"It confirms that even relatively low levels of exposure to radioactive fallout can result in genetic effects," he said.
If Møller and colleagues are right, then millions of people living in Belarus, Ukraine, and Russia are still at risk.
"With proposals to increase the use of nuclear energy," Baverstock said, "this is a matter that needs urgent attention."
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