Birds in the exclusion zone around Chernobyl are adapting to - and may even be benefiting from - long-term exposure to radiation.

Ecologists have found evidence that wild animals were adapting to ionising radiation from the worst nuclear disaster in history. Birds that produce the most pheomelanin, a pigment found in feathers, have the greatest problems coping with radiation exposure, said researchers.

"Previous studies of wildlife at Chernobyl showed that chronic radiation exposure depleted antioxidants and increased oxidative damage. We found the opposite - that antioxidant levels increased and oxidative stress decreased with increasing background radiation," said Dr Ismael Galván, of the Spanish National Research Council.

The Chernobyl disaster on 26 April, 1986, had catastrophic environmental consequences. But because the area remains heavily contaminated by radiation and is closed to the public, the region represents an accidental ecological experiment to study the effects of radiation on wild animals.

The researchers used mist nets to capture 152 birds of 16 species at eight sites inside and around the Chernobyl exclusion zone. They measured the background radiation levels at each site, while taking feather and blood samples from each bird.

They then measured levels of glutathione, an important antioxidant in plants, animals and fungi, as well as oxidative stress and DNA damage in the blood samples. The researchers also checked levels of melanin pigments in the feathers.

Melanins are the most common animal pigments, but because the production of pheomelanin (one type of melanin) uses upantioxidants, animals that produce the most pheomelanins are more susceptible to the effects of ionising radiation.

The team used a method which focused on individual birds instead of species averages, making it a more sensitive way to analyse biochemical responses to radiation. In this way, the study takes into account how closely related different species are.

The species surveyed were: Red-backed shrike, great tit, barn swallow, wood warbler, blackcap, whitethroat, barred warbler, tree pipit, chaffinch, hawfinch, mistle thrush, song thrush, blackbird, black redstart, robin and thrush nightingale. Levels of radiation in the study area ranged from 0.02 to 92.90 micro Sieverts per hour.

The results revealed that with increasing background radiation, the birds' body condition and glutathione levels increased and oxidative stress and DNA damage decreased. Birds which produced larger amounts of pheomelanin and lower amounts of eumelanin pay a cost in terms of poorer body condition, decreased glutathione increased oxidative stress and DNA damage.

"The findings are important because they tell us more about the different species' ability to adapt to environmental challenges such as Chernobyl and Fukushima," said Galván.

Ionising radiation damaged cells by producing free radicals, toxic molecules within cells. It is known that low doses of radiation increases an organisms ability to resist larger, subsequent doses of radiation.

The study was published in the British Ecological Society's journal Functional Ecology.