Scanning electron micrograph (SEM) of a down feather from a lanner falcon (Falco biarmicus). Down feathers are simple feathers beneath the external feathers, which help to insulate the bird. They lack the organised blade-like structure of the external and especially the flight feathers, instead having a short central stem (rachis, not seen), relatively few barbs (one seen here) and fine barbules that lack the interlocking hooks of the outer feathers. The lanner is a large falcon that inhabits open country in Africa, southest Europe and western Asia. The barbules here move due to electrostatic interactions during the scans.