The bird life at M vatn is characterized by ducks . Densities of breeding ducks are exceptionally high and the species composition is unusual.
Ducks comprise a group of species which at first glance seem to have similar habits.
When examined more closely the various species turn out to be quite different in their way of life. One character which the duck species share is the difference in plumage between the sexes. The drakes attain their colourful plumage in autumn before the birds pair and keep it until the following summer. In the middle of the summer the males moult their flight feathers and become flightless. The body plumage becomes dull and resembles that of the females - they get into eclipse.