Pintails are very attractive ducks with long necks and the long tail for which they're named. The first photo is a pair - the male is smartly coloured with the brown head and white stripe up the neck, while the female is brown with the neat patterning to the feathers. The last two are of males in eclipse plumage. Eclipse plumage occurs while a male is undergoing a moult and helps to camouflage the bird while it cannot fly and is vulnerable.
1: River Aare, Dählhölzli, Bern, 13/10/2007.
2 and 5: River Aare, Dählhölzli, Bern, 20/10/2007.
3-4 and 6: River Aare, Dählhölzli, Bern, 29/11/2008.