A study, carried out by a scientific team from the Rey Juan Carlos University and the National Museum of Natural Sciences (MNCN-CSIC), experimentally examined whether birds have the ability to adjust their color 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 in the newly developed feathers," explained Isabel López Rull, URJC researcher and co-author of the study.
The study of changes in the morphology, physiology and behavior of organisms as a function of the temperature and humidity conditions of their environment is important while interpreting current biogeographic patterns as an analysis of 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 body temperature through metabolism, such as birds and mammals.
The results of this research, published in the scientific journal Scientific Reports, reveal that they have the ability to change 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 provided the first unequivocal evidence that the individual ability of birds to adjust their color could be a possible adaptation to climatic environments in endothermic animals”, underlines MNCN researcher Juan Antonio Fargallo.
Gloger's rules
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 case, a key point to understand the mechanism of this theory is probably whether endotherms have the ability to change color in response to temperature and humidity. As Isabel López Rull explained: "If the endothermic animal has the ability to vary its coloration and humidity promotes its darkening, as is assumed by Gloger's rule, birds housed in a humid environment may be darker than birds." birds housed in a dry environment”.
Based on this hypothesis, the experiments carried out with the han demonstrated that plumage coloration in response to humidity 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 occurred between July and September- and to guarantee that at the end of the treatment all the birds developed a new plumage “After six months from the start of the treatment, we measured the coloration of the plumage 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”, says the URJC researcher.
This work was part of the research project "Environmental variation in melanic color: an experimental approach to the mechanisms underlying Gloger's rule", the main researcher is Isabel López Rull.
