Regarding how, female v hard to distinguish. Male Leaden appears grey rather than black above but both glisten blue. Border with white across breast on Satin (down turned think "s" for sad face), Leaden (up turned smile think "L" for laughing). This is a little obscured by twig but is clearly a smiley face for Leaden.
They aren't easy. Other factors to keep in mind include habitat preference. You will find Leadens breeding around town but Satins breed up in the higher wetter forests in Namadgi. Satins however will pass through Canberra on their migration (around Sep/Oct and March). The other factor is the colour of the male plumage, which is very relative to each other but as you see enough of each species you get the hang of. Under certain lighting conditions which can be hard to tell in photos, Leadens can appear really dark (as has happened in image 1), however Satins will of course keep the deep blue-black colour. The third photo was very good and shows that the bird is much too blue-grey rather than black with a blue sheen. With females, other than inferring likelihood from habitat, you generally just have to hope there is a male around. A good resource with some nice photos and description is on Graeme Chapman's site (links at the end). It also mentions a difference in the colour of the male's undertail shaft colour, if you get a photo from directly below. Thanks Richard for your input, will change Chris' confirmation. http://www.graemechapman.com.au/library/viewphotos.php?c=184 http://www.graemechapman.com.au/library/viewphotos.php?c=181