The paper presents indicators of the number, reproduction and behaviour of mallard ducks living in non-urban and urban environments in the Lublin region. The research carried out in urban and rural areas showed significant differences in the behaviour of birds reflecting their timidity in the presence of humans, measured as the distance from the observer at which they took flight and subsequently landed on the water surface. These distances were four times greater in the non-urban areas. Total numbers of birds and bird density indicators were significantly higher in the urban areas, as was the average size of the assemblages, by 2,0-3,2 birds, depending on the date of the study. There were no significant differences in sex structure or reproductive rates between the study sites, with male predominance in all study areas. The analyses indicate progressive adaptation to urban environments by mallard ducks. This is achieved through behavioural changes, which do not significantly affect the course of natural selection or breeding processes in birds present in these environments, which remain similar to those observed in non-urban or low-urbanized environments typical for this species.