Both male and female blue tits have feathers on the top of their heads which reflect ultraviolet light.

To detect any changes in chick-rearing behavior based on the female blue tits’ appearance, a team from the Konrad Lorenz Institute of Ethology in Vienna covered the females' crown feathers with an oily compound that blocks UV light.

They waited until after the birds’ chicks had hatched before starting the experiment.

While the chemicals did not alter how the females behaved, researchers found the males made fewer hunting trips to feed their broods.

But the males were found to exert the same amount of effort to protect their nests and defend their chicks as those whose females did not have the UV-blocking oil.

The study, published in the journal Frontiers in Zoology, concludes that female blue tits must invest a lot of time preening to remain attractive to their mates.

Photo: Marko K - Flickr