Climate change is making birds less colourful, according to a 15 year study on the common bird — the blue tit.

The blue tit, renowned for its striking blue crest and yellow breast, relies on its flashy plumage to attract mates.

As their feathers get dull, the survival of the birds might be threatened. It is feared that the phenomenon could reduce the number of new chicks.

‘Traits such as colouring function as signals to indicate to other individuals the quality of the specimen. They are decisive, for example, when it comes to breeding,’ said Dr David Lopez-Idiaquez, lead author of the study.

Two populations in the south of France were tracked for 15 years — one on the outskirts of Montpellier and the other on Corsica.

The results published in the journal The American Naturalist identified average reductions in colour in both groups between 2005 and 2019.

‘Our work suggests environmental changes, and specifically climate change, could be the main reason why birds such as the blue tit are undergoing a change in their physical features, more specifically in the brightness and intensity of their colouration,’ said Dr Lopez-Idiaquez.

‘A negative trend in terms of brightness and intensity of plumage colouration in both sexes and populations has been observed, although in Corsica this change is more associated with climate,’

The change in plumage colour seems to be the result of a combination of a rise in temperature by 1.23ºC and a fall in rainfall by 0.64 mm. Clearly, the cause of this difference here is climate change.

Colour differences between sexes in birds is known as ‘sexual dichromatism’. Female preference for bright colours in males was observed by Charles Darwin and formed part of his ‘theory of evolution.’

Each year during the study period all breeding blue tits were captured, enabling more than 5,800 observations on colouring and other characteristics.

The birds’ colouring has an effect on the mating patterns of the species, putting their very presence at risk, warned the international team.

There are only four studies of this type in the world, and the first one to be carried out in the Basque Country.

‘It is important to stress this change is not genetic but plastic, one of the ways of adapting to new environmental conditions. Given our environment is quite similar, albeit less hot, our birds may be undergoing the same change,’ said Dr Lopez-Idiaquez.

When there is a variation in territory animals can undergo genetic change or alter physical characteristics. They can also migrate – or disappear.

Last month, a University of Sheffield study also found that birds were adapting to global warming by shedding distinctive features.

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