A new study in the Royal Society's Biology Letters has dismissed the notion that the exclusion zone around the Chernobyl nuclear power plant has created a wildlife haven.
Recent studies said rare species had thrived there despite raised radiation levels.
But scientists who assessed the 1986 disaster's impact on birds said the ecological effects were "considerably greater than previously assumed".
Researchers Anders Moller of University Pierre and Marie Curie, France, and Tim Mousseau from the University of South Carolina, US, said they found evidence that low-level radiation was affecting the animals even in the exclusion zone.
"Recent conclusions from the UN Chernobyl Forum and reports in the popular media concerning the effects of radiation from Chernobyl have left the impression that the exclusion zone is a thriving ecosystem, filled with an increasing number of rare species. This is not scientifically justified," the researchers wrote in their study.
"Instead, the species' richness, abundance and population density of breeding birds decreased with increasing levels of radiation," the BBC quoted the study as saying.
The study, which recorded 1,570 birds from 57 species, found that the number of birds in the most contaminated areas declined by 66 percent compared with sites that had normal background radiation levels.
It also reported a decline of more than 50 percent in the range of species with increasing radiation levels.
In April 1986, reactor number four at the Chernobyl Nuclear Power Plant exploded. After the accident, traces of radioactive deposits were found in nearly every country in the northern hemisphere.