Swifts are expert fliers capable of staying in flight for several months without stopping. To achieve this, they need to keep their plumage in excellent condition! It is through feather care, or "preening", that the birds eliminate dust, dirt and parasites, as well as maintain the elasticity, shape and position of their feathers. Like other activities (catching prey, drinking and mating), preening is also carried out by swifts during flight.
These actions are so fast that they go mostly unnoticed even by the most keen observers, and only slow-motion and close-up videos are able to provide an accurate description of these behaviours.
By analysing the videos of the ornithologist Jean-François we realise that by leaning backwards, swifts manage to reach the uropygial gland which secretes an oil rich in waxes, fatty acids and water. This oil is then spread with the beak over the feathers on the back, belly, tail and wings. Head and neck feathers are maintained by the legs: despite having very short legs, swifts are able to slip them under the wing to reach these parts.
Check out some of these movements here!