Abstract
Carotenoid staining has been repeatedly shown to serve as a sexually selected individual quality signal. In different species, individuals that show brighter carotenoid-based signals have been found to have superior feeding abilities, recover faster from disease, and generally enjoy better body condition. In the common crossbill (Loxia curvirostra), the colour has also been related to the different populations, with northern and central European populations being described as redder than those in the Mediterranean region. A study in the Pyrenees showed that long-winged individuals had lower apparent survival, and the proportion of red individuals was higher in long-winged birds, concluding that they could be nomadic birds (that travel long distances). A priori, if the red crossbills are more mobile than the yellow and orange ones, their apparent survival will be lower. However, in our study, red males showed a greater survival than males of other colours and almost double than that of the yellow ones. These results suggest that red coloration is linked to higher quality individuals regardless of their mobility.
Highlights
Avian coloration largely depends on pigments deposited in plumage or bare parts (Prum 1999)
The annual p values ranged from 0.018 ± 0.018 to 0.42 ± 0.06. This is the first study where the apparent survival of wild male Crossbills is calculated in relation to their colour pattern, ranging from yellow to red
The carotenoid-based red coloration originates from the ingestion of yellow carotenoids that are subsequently converted into red ketocarotenoids (3-hydroxy-echinenone; Del Val et al 2009b; Cantarero et al 2020)
Summary
Avian coloration largely depends on pigments deposited in plumage or bare parts (Prum 1999). Carotenoid pigments generate conspicuous yellow, orange, and red colorations in many avian species (Fox 1976; Stradi et al 1996). These colours depend on pigment concentration and on the specific nature of each carotenoid compound (Hill et al 2002). Carotenoid transformation has been linked to mitochondrial metabolism (cell respiration; Hill 2011; Johnson and Hill 2013) In this case, red ornaments indicate the intrinsic quality of an individual as it would be unable to regulate (balance) its expression regarding to any other function (i.e. individuals could not be able to cheat about its capacity to express colour; Hill 2011; Johnson and Hill 2013)
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