sentences:  Nestlings with a bird rich diet have higher levels of circulating carotenoids and display a greater carotenoud based colouration than those consuming more mammals.However, both circulating carotenoids and carotenoid based colouration have been shown to be affected by non-organic (like heavy metals) and organic (like persistent organic pollutants) contaminants.These pollutants may interfere with the communication processed that rely on carotenoid coloured traits.