Barn owls display larger black feather spots in cooler regions of the British Isles

Abstract

Although, in many organisms, genotypes are adapted to specific environmental conditions, the identification of the ecological factors explaining patterns of local adaptation is not a trivial task. In relation to the cosmopolitan barn owl (Tyto alba), its plumage varies from white to dark pheomelanic and shows a difference in the number and size of black spots located at the tip of ventral feathers. The expression of these traits is strongly heritable and weakly sensitive to variation in body condition. Therefore, if owls located in cold or rainy regions are differently plumaged compared to owls living in warm or dry regions, this may not be a result of climate affecting the expression of plumage traits. Instead, different plumages might be selected under different environmental conditions. We have found that, on the British Isles, comparatively larger spots are present on barn owls found in regions that are cooler in summer. This is similar to the findings of a previous study performed in North America and on continental Europe, raising the possibility that larger-spotted barn owls better cope in cold temperatures during the rearing period or that they are better adapted to some environmental factors prevailing in cooler summers.

Climate‐driven convergent evolution of plumage colour in a cosmopolitan bird

“…Although these traits are partly genetically linked (Roulin & Jensen, ), this difference might be explained by the fact that black spots cover a small proportion of the plumage surface, thus limiting their scope to be involved in camouflage, feather resistance or body‐drying functions, and because spottiness seems to be more involved in mate choice and sexual selection than plumage colouration (Antoniazza et al, ; Roulin & Ducrest, ; Roulin, Jungi, Pfister, & Dijkstra, ; Roulin et al, ). However, this result apparently contradicts previous studies at smaller scales reporting that individuals with larger spots are more abundant in colder regions (Roulin & Randin, ). We cannot exclude that spot size can help to thermoregulate, as suggested in T. javanica , but in the other two lineages such a possible function might have been masked in the present analyses because populations living in tropical and warmer habitats are more spotted than those at temperate latitudes, as indicated by the negative trend of spot size with latitude consistently observed in all the lineages (Table ; Roulin et al, ).…”

Darker where cold and wet: Australian birds follow their own version of Gloger's rule

“…Genes affecting the deposition and synthesis of melanin are linked to important physiological processes, such as stress responsiveness, basal metabolic rate, immunity, or behavioural traits (reviewed by Ducrest et al 2008). Hence, selection acting on these behavioural and/ or physiological traits could be driving the correlations between coloration and climate (Roulin and Randin 2016). Research on polymorphic owl species (Fam.…”

Latitudinal variation in biophysical characteristics of avian eggshells to cope with differential effects of solar radiation

“…The study of geographical variations in phenotypic traits is useful in the understanding of the selective agents that shape the phenotypic variation (Roulin & Randin, ). Our results indicate that eggshell reflectance in the Kentish plover across a latitudinal gradient, both in the human visible and UV spectrum, is primarily determined by spatial variations in solar radiation, and that this may also affect egg size in a way that has not been appreciated in previous studies (see Williams, ).…”