Directional movements of Fieldfare (Turdus pilaris) according to long-term year-round morning counts in two locations of the Moscow Region
Authors:   State Darwin Museum, Kontorshchikov V.V. 
Published: September 2024

The Fieldfare in the Moscow Region is a common breeding, migrating and wintering species. In 20102022, year-round two-hour morning counts of directional bird movements were conducted in two villages of the Moscow Region - Dmitrovka, Taldomsky District (56°44' N, 37°44' E) and Kopytovo, Mozhaisky District (55°28' N, 35°38' E). The latter is located 190 km south-west of Dmitrovka. Both villages are surrounded by fields, meadows, and forests; there are no obvious guiding landscape lines or ecological barriers near the observation sites. Because of the difference in the geographical position of the villages, the main changes in the dynamics of migration intensity in Dmitrovka take place, on average, about ten days later in spring, and, about ten days earlier in autumn in comparison with Kopytovo. Spring migration at the observation sites occurs mainly from the beginning of the third ten-day period of March (in some years, perhaps, from the first ten-day period of March) to early May. The peak of spring migration falls on the first and second ten-day periods of April in Kopytovo and on the second ten-day period of April in Dmitrovka. In spring, Fieldfares follow mainly to the northeast and in Dmitrovka also to the north. Fieldfares resume their directional movements since mid-June, after majority of young birds become independent. At the beginning of the post-breeding period, till the end of June in Dmitrovka and till the end of the second ten-day period of July in Kopytovo, Fieldfares fly mainly in the same directions as in spring, to the northeast and north. Presumably, this happens due both to explore new areas by juvenile birds, and to relocate before moult to northern regions with more rich seasonal food, as well as for a second breeding attempt by some adults. Later, from August to January in Dmitrovka and till February in Kopytovo, Fieldfares are heading mainly southwestward with a clear deviation to the west. The peak of such movements falls on the period from the third ten-day period of August to the second ten-day period of October in Dmitrovka or the third ten-day period of October in Kopytovo. In mid-October, there is usually a sharp upsurge in migration, when Fieldfares fly in large numbers and in large flocks. This surge of migration activity is presumably caused by the first heavy snowfall north of the Moscow Region, which prevents access to the soil, where Fieldfares prefer to feed. For some unknown reason, in Kopytovo in November, the movements of Fieldfares to the north and northeast significantly prevail, which distinguishes this month from others in this site during the period from August to February. Presumably, these are local foraging movements. The decrease in the intensity of movements after the migration peak usually occurs in two stages. The first rapid decrease occurs in the third ten-day period of October in Dmitrovka and in the first ten-day period of November in Kopytovo. The second one occurs usually in the third ten-day period of November in Dmitrovka and in the first ten-day period of December in Kopytovo. The latter probably is due to establishment of a permanent snow cover in the Moscow Region and further north. Both in spring and post-breeding period, 3-11% of birds follow in the direction opposite to the main direction of seasonal migration, which are significantly more than by chance. These reverse movements are presumably caused mainly by stresses of different origin and/or low fat reserves. It can be assumed that if a bird needs to change its location without moving to a certain familiar place, it will follow the line connecting its breeding and wintering areas, in accordance with the innate navigation program. Stress and/or low fat reserves turn the bird in the opposite direction to where it flew before.