Urban great tits have paler plumage than their forest-living relatives

"We used feather samples collected from great tits in cities and forests across Europe. Different methods all confirmed that urban great tits are paler," says Hannah Watson, biology researcher at Lund University, and one of the authors behind the study.

The yellow colour in the great tit's feathers comes from carotenoids, which the birds get from the insects they eat. These insects, in turn, obtain the nutrient from the plants they feed on. Carotenoids are important antioxidants that help the body combat the toxic effects of pollution. If great tits in cities cannot obtain enough carotenoids from their food, their plumage becomes paler, resulting in weaker defences against the adverse health effects of pollution.

"Our findings suggest that birds in the city are not getting the right diet. This can help us understand how to create urban environments that are more beneficial for biodiversity. By planting more native trees and plants in our gardens and parks we can help small birds, such as great tits, by providing them with a healthy diet of insects and spiders for themselves and their chicks," says Hannah Watson.

Surprisingly, the researchers found that the effects of cities on birds vary across Europe. For example, in Lisbon, forest great tits displayed much brighter feathers than city great tits. In Malmö, on the other hand, the difference in plumage between city and forest great tits was considerably less noticeable.

"We need further research to understand why some cities have more favourable environments for birds and wildlife than others. This can help urban planners develop biodiversity-friendly policies and improve the quality of life for people living in cities," says Hannah Watson.