Recent studies show that urban pollution may have a dulling effect on plumage, and not just among dirty birds.

Some popular city dwellers appear to be losing their colorful allure.

According to a study published this summer in the journal Landscape and Planning that looked at 547 bird species in China, birds that live in cities are duller and darker on average than their rural counterparts. A similar conclusion emerged from an analysis of 59 studies published in March in Biological Reviews: Urban feathers are not as bright, with yellow, orange and red feathers affected most.

Often, city birds are covered in grime. But even if you could give them all a good bird bath, chances are their brightness still wouldn’t match that of their country cousins. That’s because of the way pollution, and heavy metals in particular, can interact with melanin, a pigment that makes feathers black, brown and gray.

Studies show that

Keep reading this article on The New York Times Energy & Environment.