Preening feathers- most birds preen their feathers several times a day, vital to clear dirt and parasites, and to optimally align every feather for best flight, something vital to a Swallow like this, newly arrive from Africa. I was lucky to watch it preen every wing feather individually, as one photo shows. Preening also serves to spread oil from the preening gland (uropygial gland) in order to keep the feathers waterproof and from becoming brittle. I watched this Swallow. Conditions: sunny and warm as I leave Sussex! Temperature: Max 15- Min 7c.