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Bird plumage made less colourful by global warming

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After a 15-year study from 2005-2019 scientists from UPV/EHU and the Centre d’Ecologie Fonctionnelle et Évolutive in Montpellier (CEFE-CNRS) Decided that global warming is making the plumage of blue tits less colourful. They call this a “plastic change” as opposed to a genetic change in their plumage. They observed and recorded the appearance of 5,800 birds in populations in the south of France, one on the outskirts of Montpelier and the other on Corsica. Over that period of time there has been a rise in temperature in that region of 1.23°C and a decrease in rainfall of 0.64 mm.

Eurasian Blue tit

Eurasian Blue tit. Photo credit: David López-Idiáquez/UPV/EHU-University of the Basque Country.

At present, this research appears to be observational. What I mean is they have simply observed the birds and seen a decrease in the coloration of their plumage. My understanding is that they have not positively connected climate change with this dulling of plumage. I can’t see the reason why plumage becomes duller because the climate is warming up. Where is the hard connection between these two events? How does warmth make blue tits less colourful?

It has been suggested that as the coloration is less vibrant males are less likely to attract females and therefore this development may have an impact in the long term on population numbers. We know that plumage is important in attracting females.

David López-Idiáquez, of the University of the Basque Country in Spain, the study’s lead author said: “In these birds, traits such as colouring function as signals to indicate to other individuals the quality of the specimen, which are decisive, for example, when it comes to breeding. This study was possible thanks to the continuous monitoring of the two blue tit populations for more than 15 years, which highlights the importance of long-term studies to understand the effects of climate change on the ecosystems around us”.

He also said that when there is a variation in a region where there are animal populations four things can potentially happen: they can undergo genetic or plastic change as is the case in this instance, or migrate or disappear by which I believe that he means become extinct in the wild.

Feather colouring in birds

It might be useful to look at some background information about feather colouring in birds. The RSPB tell us that the colour of feathers is produced by a number of means and from time to time the mechanism that produces a bird’s normal coloration breaks down which results in a lack of colour or the colours are too bright.

As is the case with cats, dogs and humans, the main colouring agent is a pigment called melanin. This is sometimes referred to as eumelanin. It is a dark brown colour but the RSPB describes it as “black, brown, chestnut-red or yellow in colour”. Melanin hides carotenoid pigments when the two are present at the same time in the feathers.

As is the case also with eye colour and kittens, blue and greens are not due to pigmentation but the way that light is transmitted through the structure which in effect filters out other colours. It is due to the refraction of light. The RSPB calls these ‘structural colours’. The overall colour is a result of the structural colour and pigmentation.

Taking parrots which green coloration, this is due to a mixture of yellow pigmentation interacting with blue structural coloration. Yellow and blue create green. When a Kingfisher is seen in very low light conditions, they can appear to be dark in colour because their coloration is based upon structural colour which is due to the refraction of light as mentioned. Where there is no light, this does not work anymore.

Colour is used in the bird population to identify other birds and in “sex recognition and signalling of body condition, breeding condition and social status”. It is controlled by genes which are inherited. The intensity of colour can be altered by hormones. Sometimes the mechanisms break down. If the effect is a lack of coloration this may affect the ability of a bird to attract a mate or secure territory.

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