WASHINGTON, July 11 (Xinhua) -- Brightly colored birds are among the species most adversely affected by the high levels of radiation around the Chernobyl nuclear plant, ecologists said.

    The findings, published Wednesday online in the British Ecological Society's Journal of Applied Ecology, help explain why some species are harder hit by ionising radiation than others.

    Professor Timothy Mousseau of the University of South Carolina and collaborators examined 1,570 birds from 57 different species in the forests around Chernobyl at varying distances from the reactor.

    They found that populations of four groups of birds -- those whose red, yellow and orange plumage is based on carotenoids, those that laid the biggest eggs, and those that migrated or dispersed the furthest -- declined more than other species.

    The intriguing results center on the role of antioxidants, chemicals that help protect living organisms from the damaging effects of free radicals. Certain activities use up large amounts of antioxidants. These include producing carotenoid-based pigments for feathers, migrating long distances and laying large eggs (birds will deposit larger amounts of antioxidants in larger eggs).

    Researchers hypothesized that because they had fewer antioxidants left to mop up dangerous free radicals, these birds would most adversely affected by exposure to radiation around Chernobyl.

    Among the brightly colored species most affected were orioles, blackbirds and blue tits, while drab species like tree pipits, coal tits and chaffinches were much less affected. Long distance migrants or dispersers that were most affected included quails, orioles, hoopoes, blackbirds and robins, while non-migrant or short-dispersing species like great tits, coal tits and song thrushes were much less affected.

    "This is the first study linking the effects of radiation on population size of different species to antioxidant defense. Although all species must cope with the potentially detrimental effects of free radicals, because of their use of antioxidants, certain species are predisposed to suffer most from these negative effects," they said.