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Irene Vega
The study of changes in the morphology, physiology and behavior of organisms depending on the temperature and humidity conditions of their environment is important both to interpret current biogeographic patterns and to analyze their possible adaptation to climate change. However, despite the relevance of these investigations, there are few studies on color variations in response to climate in endothermic animals, that is, those that are capable of regulating their body temperature through metabolism, such as birds and mammals.
The objective of the work, carried out by a scientific team from the URJC and the MNCN-CSIC, has been precisely to examine experimentally whether birds have the ability to adjust their coloration to adapt to environmental conditions. “Specifically, we tested whether house sparrows (Passer domesticus) change their coloration when faced with variable humidity conditions. To do this, we exposed the birds to two environments with different relative humidity (wet versus dry) six months before the moulting season and, once the feathers had moulted, we measured the coloration of the newly developed feathers," explains Isabel López Rull, URJC researcher and co-author of the study.
The results of this research, published in the prestigious scientific journal Scientific Reports, reveal that birds are capable of changing their color in response to an environmental variable. “The sparrows in the wet treatment developed darker plumage than those in the dry treatment. Our result provides the first unequivocal evidence that the individual ability of birds to adjust their coloration may be a possible adaptation to climatic changes in endothermic animals", underlines MNCN researcher Juan Antonio Fargallo.
Check that Gloger's rule holds
A classic ecogeographic rule linking coloration of endothermic animals to climate is Gloger's rule, which predicts darker individuals (those with more pigment in their feathers or fur) in warm, humid regions. In this sense, a key point to understand the mechanism of this theory is to test whether endotherms have the ability to change their coloration in response to temperature and humidity. As Isabel López Rull explains: “If endothermic animals have the ability to vary their coloration and humidity promotes their darkening, as is assumed by Gloger's rule, birds housed in a humid environment should be darker than birds. birds housed in a dry environment”.
Based on this hypothesis, experiments with birds have shown that plumage coloration in response to moisture is consistent with the predictions of Gloger's rule.
To carry out these verifications, the duration of the experimental treatment had to be six months in order to cover the period of feather moulting -which in sparrows occurs between July and September- and to guarantee that at the end of the treatment all the birds had developed a new plumage “After six months from the start of the treatment, we measured the coloration in different areas of the body using a spectrophotometer and digital photographs. At the end of the experiment, the birds were released at their place of capture”, points out the URJC researcher.
This work is part of the research project "Environmental variation in melanic coloration: an experimental approach to the mechanisms underlying Gloger's rule", whose principal investigator is Isabel López Rull.