Structure and Long-Term Fluctuations in the Wintering Mallard (Anas platyrhynchos, Anseriformes, Anatidae) Population in the City of Moscow

Abstract—The structure of and long-term fluctuations in the wintering mallard (Anas platyrhynchos) population were studied from 1985 to 2016 in the city of Moscow. The number of wintering mallards was counted annually on the same day at all ice-free ponds and rivers of Moscow. The total winter population of mallards increased 1.6–3.3 times compared to the summer one. The growth of the wintering group continued from 1985 (17 200) to 1990 (27 900). From 1991 to 1998 its size decreased to 7500, remained low until 2002–2003, after which it began to grow up to 29 700 in 2015. The freezing season has decreased from 132 to 104.5 days (Z = 3.8, p = 0.0001, n = 32) during the study period. At the same time, the average air temperatures of November and December have increased significantly. Mallards gather at the southeastern urban section of the Moscow River exclusively in the cold season. There is no correlation between mallard numbers and interurban winter clusters. This gave grounds to divide the total bird numbers conditionally into the riverine and interurban groups, which were analyzed separately. The size of the interurban group correlates with the duration of the freezing season (r = –0.47, p = 0.006, n = 32), while that of the riverine group correlates with the average (r = 0.41, p = 0.02, n = 32) and minimum (r = 0.54, p = 0.001, n = 32) winter temperatures. The proportion of mallards that wintered in the Moscow Zoo changed in the opposite direction compared to the size of the interurban group (r = –0.83, p < 0.01, n = 32). The numbers of mallards wintering at internal water bodies correlates with the purchasing power (r = 0.44, p = 0.012, n = 31) and welfare of citizens from 1985 until 2015. The more rapid growth in the size of the wintering interurban group compared to the riverine group indicates the advantages of living in urban conditions. These are the lack of permanent human persecution, additional food sources, and a milder climate.