http://www.economist.com/news/science-and-technology/21584963-birds-live-cataracts-chernobyl-not-so-blindingly-obvious

Radiation and birds
Not so blindingly obvious
Birds live with cataracts in Chernobyl
Sep 7th 2013 |From the print edition

CATARACTS are relatively common in people who live to a ripe old age. They are sometimes seen in animals that live in zoos as well, but in the wild they are almost unheard of. The reason is simple. Losing eyesight is in effect a death sentence for a wild animal that must find its own food and, should that animal live long enough to develop the disease, starvation or predation would quickly follow. But cataracts unrelated to age are surprisingly common in birds living near the site of the Chernobyl nuclear disaster in 1986.

This is revealed in a new study by a pair of ornithologists, Timothy Mousseau of the University of South Carolina and Anders Moller of the University of Paris-Sud, which is published in the Public Library of Science. That cataracts and ionising radiation are related is well known. As high energy ions, usually produced by the sun’s rays, slam into the water found next to the lenses of the eyes, free radicals are created that damage DNA and cause errors to develop in the formation of proteins that make up the lenses, resulting in cataracts.

<snip>

In all, 391 of the birds the researchers caught had cataract scores of one or more, and were thus suffering some level of visual impairment. However, contrary to the way cataracts work in the rest of the world, those in the eyes of birds living near Chernobyl appeared regardless of whether they were young or old. When Dr Mousseau and Dr Moller examined their radiation measurements, they found that the key factor determining the presence of the disease was the intensity of local radiation, with cataract scores of over one proving to be far more common in areas that were above ten microseiverts per hour.

The twist in this story, however, is that in a previous study Dr Mousseau and Dr Moller reported last year that, compared with the bird populations near the site of the Fukushima nuclear disaster in Japan, the birds around Chernobyl seemed able to tolerate the effects of radiation better. This finding hinted that natural selection was already under way and that birds unable to cope with high radiation levels had already been culled from the Chernobyl population, leaving behind only those most suited for survival. Exactly which traits were being selected for by this vicious process remains a mystery, but with the discovery of so many birds living with cataracts it seems likely that being able to function with limited vision is one.