Sunning may be beneficial to birds in several ways. It could be a way of regulating their body temperature. The spreading of feathers may help dislodge parasites or loosen them for re-distribution. It is also possible that sunning maximizes vitamin D, an essential nutrient to keep the bird healthy (humans too!).
Scientists are not exactly sure why birds sun themselves, but whatever the reason, it's a treat to witness this interesting behavior in a variety of avian species. Keep an eye out for birds catching a few rays the next sunny day in the field!
photo © adrian binns