Knobbelzwanen in de stad Groningen in strenge winters

During the severe winter of 1981/1982, up to 144 wintering Mute Swans Cygnus olor were recorded in the city of Groningen (The Netherlands). A large majority of them could be trapped and ringed and the results are presented in this paper, together with results of ringing studies on Mute Swans wintering in the city of Groningen during the severe winter of 1978/1979. Table 1 presents counts at one particular site during the winter season of 1981/1982; table 4 presents counts in the city of Groningen during the period 1979 - 1983 ('jan' = January, 'febr' = February, 'mrt'= March). Figure 1 presents a map with the ringing sites of ringed Mute Swans that were recovered in Groningen during the winter of 1978/1979. Figure 2 presents a map with the recovery sites of the Mute Swans that had been ringed in Groningen during the winter of 1978/79. Figure 3 presents a map with the ringing sites of ringed Mute Swans that were recovered in Groningen during the winter of 1981/1982. Figure 4 presents a map with the recovery sites of the Mute Swans that had been ringed in Groningen during the winter of 1981/1982. Table 3 presents data on the colour-morph of Mute Swans, based on ringed individuals. ('Donkere poten' = dark colour-morph, 'Vleeskleurige poten' = light colour-morph.).