The advantages of joining a local wildlife group are numerous; not least is having local experts to call on and also field trips to join. Yesterday I went to a reserve that was new to me - Wigan Flashes. Although we didn't see the bittern that has been seen there earlier in the week, we did see lots of water fowl and I learnt to distinguish a gadwall from all the other brownish female ducks.Above L is a female gadwall, R is a male. Although not always visible, the white patch on the plumage helps gives distinguish a gadwall from other female ducks.
Photo of Wigan Flashes copied from http://www.lancswt.org.uk/Our Reserves/wigan_flashes.htm
Photo of Gadwall used by kind permission of Dave Appleton www.gobirding.eu See link