Air pollution is fading the bright colours of great tits Parus major, with possible dire consequences, according to new research from Finland.
Coloured plumage plays an important role in the communication of many birds: the brighter your show, the healthier you appear, and these signals serve both to attract potential mates and warn off competitors.
A recent study by Tapio Eeva and colleagues at the University of Turku, Finland, of great tits at varying distances from a source of air pollution (a copper smelting plant in South-west Finland) has produced worrying results: the yellow plumage of young great tits is significantly paler the closer to the source they live.
The pigments responsible for colouring feathers yellow are derived from chemicals called carotenoids. Birds cannot make these chemicals themselves and so must obtain them indirectly through what they eat. The problem is that pollutants emitted from the smelting plant are causing a decrease in the number of green caterpillars, an important component of great-tit diet generally and a vital source of carotenoids. Even when great tits do get a carotenoid-containing mouthful, pollutants may interfere with the chemical process by which the carotenoids are converted into yellow pigments, fading feathers further.
As a result of these knock-on effects, the scientists found birds from polluted areas are smaller and duller, which may reduce their ability to compete for food and mates - and damage their chances of survival
(Functional Ecology, vol. 12, p607-12).