Dynamics of the Structure and Numbers of the Urban Population of the Tufted Duck (Aythya fuligula, Anseriformes, Anatidae) in Moscow.

The structure and numbers of the urban population of the tufted duck (Aythya fuligula) in Moscow were studied. Wintering birds over 36 seasons, 1985−2021, on ice-free water bodies, as well as females with broods and the number of ducklings in each brood for 24 seasons, 1998−2021, on 150 ponds and 23 rivers of Moscow were counted. The date of the onset of egg-laying by females was calculated using the countdown method, based on the age of ducklings. The size of the wintering group from 1985 to 2009 averaged 32 (1–75) birds. This number increased to an average of 174 (111–332) birds for the period 2010–2021. The number of nesting females with broods changed from 11 to 45, with an average of 27 broods occurring annually. The size of the wintering group correlated with the length of the frosty period and with the average daily November and December air temperature, as in the case of mallards and goldeneyes. The winter abundance of tufted ducks correlated with the adult females number in the following summer. The similarity of the tufted duck, goldeneye, and mallard breeding cycles is in ordering the onset of egg-laying to the transition of the average daily air temperature over 0°C. The earlier positive temperatures are established and the earlier the ice melts, the more time the females had for getting prepared for egg-laying. In summer, the number of adult ducks, broods, and ducklings increased from 1998 to 2009. The number of broods and ducklings decreased, and the number of adult birds did not change significantly from 2010 to 2021. The ratio of the number of young and adult birds decreased during the observation period. In the population of the tufted duck, the consequences of overcrowding were manifested to a lesser extent than in the mallard. They are the lengthening of the egg-laying period and the reduction in the brood-size related to an increase in the females number. The dynamics of the spatial distribution of nesting tufted ducks in Moscow at the early stages was determined by the distribution of colonies of black-headed gulls, with which they formed joint settlements. Subsequently, this dependence weakened. [ABSTRACT FROM AUTHOR]