LAUSR

From 1985–1998 to 2017, the numbers and structure of the urban population of the goldeneye (Bucephala clangula) were studied in the city of Moscow. Wintering birds and females with ducklings were counted on 150 ponds and 23 creeks of Moscow. Based on the age of ducklings, the date of the onset of egg-laying by females was calculated using the countdown method. The size of the wintering group has grown significantly since 1993 (rs = 0.92, p < 0.05, n = 25). It reached 2400 birds by 2014. Since 2010, there has been a gradual shift of wintering goldeneyes from outside the city to within its borders. The increase in numbers, like that of the mallard, correlates with local climatic indices: the length of the period of frost (rs = –0.73, p < 0.05, n = 25) and the mean daily air temperature (rs = 0.42, p < 0.05, n = 25) do not correlate with the global Index of the North Atlantic Oscillation. The breeding cycles of the goldeneye and mallard are similar in the ordering of the onset of egg-laying in relation to the transition of the average daily air temperature towards over 0°C. The earlier temperatures above freezing are established and the ice melts, the more time the females have to prepare for egg-laying for both goldeneyes (rs = –0.80, p < 0.05, n = 18) and mallards (rs = –0.77, p < 0.01, n = 18). In the nesting goldeneye group, in contrast to the mallards, changes were not observed in the timing of reproduction and in the regulation of the negative effects of overstocking, such as an extended egg-laying period and a reduction of brood size in response to increased female numbers. The numbers of nesting goldeneyes grew from 1998 to 2010 up to 57 broods, but in 2017 it dropped to 4. The negative consequences for the local population are primarily associated with winter weather anomalies that lead to the death of trees and their removal by communal services in the habitats of goldeneyes. The goldeneye population sizes in winter and summer vary in the opposite directions, this being caused by multidirectional trends in habitat transformation. The population dynamics of nesting goldeneyes largely depends on the frequency of dangerous meteorological events, while the population dynamics of wintering goldeneyes depends on the regional climate changes.