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Female birds find color important in their favorite mates. However, metal contamination nowadays is dulling feathers and making feathers less alluring. Mercury, copper and chrome, which are part of the atmosphere, are getting toxic to living species, says a news release.

Scientists from the Spanish Foundation for Science and Technology have come to the conclusion after examining the effect of toxic metals on the physiology and reproductive success of male great tits (Parus major).

These birds can be seen all through Europe with "distinguishing feathers, a black head and neck, bright white cheeks and olive-to-yellow colored bellies."

Mercury, especially, has brought down the bright yellow feathers, as it reacts negatively with carotenoids, pigments leading to the yellow color. This makes the male tit less attractive.

"The yellow coloring of the male is an indication to the female of its state of health and ability to find food. Therefore, a paler yellow great tit, as a result of exposure to mercury, will be less attractive to females," Joan Carles Senar, one of the study researchers from the Museum of Natural Sciences in Barcelona, explained.

Chrome too makes the bird dull when it reacts with the black color. "The 'black tie' is a sign of dominance and aggression in defense against predators, as well as being linked to aspects relating to the bird's personality," Senar added.

On the other hand, copper reacts with melanin and enhances its black "neck tie."

Their study was recently published in the Journal Science of the Total Environment.