Sunbathing behaviour by Red-rumped Swallows

On 3rd June 2011 at the Acebouche Visitor Centre in the Coto Donana National Park, Andalucia, Spain, I observed and photographed a group of Red-rumped Swallows Cecropis daurica. The weather was fine and extremely hot, about 35-40°C. As I walked onto a concrete apron by the Visitor Centre I noticed a group of Red-rumped Swallows lying on their sides and backs without apparent use of their legs...