Dust bathing or sand bathing is an animal behavior characterized by rolling or moving around in the dust, dry earth, or sand, with the likely purpose of removing parasites from fur, feathers, or skin. Dust bathing is a maintenance behavior performed by a wide range of mammalian and avian species.
Birds cower close to the ground while taking a dust bath, vigorously wriggling their bodies and flapping their wings. This disperses loose substrate into the air. The birds spread one or both wings which allow the falling substrate to fall between the feathers and reach the skin. The dust bath is often followed by thorough shaking to further ruffle the feathers which may be accompanied by preening using the bill.
I photographed this Oriental pied hornbill inside the Manas National Park, while it was taking a dust bath in the middle of the road.