Thermal consequences of turning white in winter: a comparative study of red grouse Lagopus lagopus scoticus and Scandinavian willow grouse L. l. lagopus

The red grouse Lagopus lagopus scoticus differs from the willow grouse L. l. lagopus of mainland Europe in not developing a white winter plumage. Previous studies have suggested that plumage colouration in birds can have important consequences for heat transfer through the feather layer. We examined the thermal consequences of plumage colouration in both subspecies of grouse. There were no differences in feather density, plumage depth or thermal resistance of the plumage between dark rufous Scottish and white Scandinavian grouse. In still air, heat gained from simulated solar radiation was greater through dark than through white plumage. However, in wind there was no difference in heat load between dark and white plumages. Our study suggests that there may be a trade-off between thermal and camouflage benefits of plumage colour for grouse in the wild.