Combination of a metal ring, a small coloured metal rings and a c-ring with a two alpha code.
note 1 : used colours for the c-ring are blue, green and red.
note 2 : used colours for the coloured metal ring are pink, orange, lilac and green.
note 3 : to the small coloured metal ring : 2 rings on each leg in a mix of colour and shape, due to better individual recognition.
note 4 : up to 100 marked individuals of Carrion and Hooded crows, marked during spring/summer 2010 in Vienna/Austria.
note 5 : this project is ended, rings are not used anymore and birds are still alive.