Timing and direction of movements, group size and some features of foraging behaviour in bullfinches Pyrrhula pyrrhula migrating through the Moscow oblast based on visual observations at two sites

The Bullfinch Pyrrhula pyrrhula in the Moscow Oblast is a common breeding, migrating, and wintering species. In 2010-2023, I conducted year-round two-hour morning counts of directional bird movements in two villages of the Moscow Region - Dmitrovka (Taldomsky Raion, N56о 44′ 60″ E37о 44′ 28″ 44.469’) and Kopytovo (Mozhaisky Raion, N55о 28′ 42″ E35о 38′ 8″). 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. Spring migrations of Bullfinches in the Moscow region may occur from the 2nd decade of February to the 2nd decade of May. The main direction of this migration is NE, possibly N-NE-NE. The peak of the migration occurs in March and the first two decades of April. Directional movements of Bullfinches after the nesting period resume from the 3rd decade of June. The number of flying Bullfinches is low until the 2nd decade of September, with a slight increase in migration activity during the 3rd decade of July to the 2nd decade of August. Apparently, this period corresponds to the period of juvenile migration of young birds and post-mating migration of adult birds, which occurs in birds before the start of moulting (Noskov 2020). Movement direction from the 3rd decade of June to the 2nd decade of September is predominantly bimodal, with some birds flying N and NE, and others to S, SW and W. The former directions may predominate at the beginning, and the latter - at the end of the period. The pronounced migration of Bullfinches to SW starts in the 3rd decade of September - 1st decade of October and may continue until the end of January. This migration peaks in October and the 1st decade of November. The intensity of migration gradually decreases from November to January. It is possible that Bullfinches fly to SW with a slight incline towards S - to S-SW-SW, i.e. exactly in the opposite direction to the spring migration. Because of the difference in the geographical location of the villages, the main changes in the dynamics of migration intensity in autumn in the first village occur, on average, about ten days earlier. A very small proportion of Bullfinches, about 1-5 %, are characterised by non-random movements in the opposite direction to the main direction of migration during this period. These movements are probably related to stresses of various origins, which in birds, especially - in individuals with low fat reserves, temporarily reverse the direction of movement in the navigational program. It is likely to be adaptive in nature. During migration, Bullfinches mostly keep singly or in twos, sometimes in groups of up to 25 individuals. Twos in late autumn, winter and spring appear to be most often male and female pairs. Bullfinches clearly avoid joining into large groups: the frequency of encounters of groups of different sizes decreases as their size increases. In spring and late June - early September the combined proportion of singles and twos is about 60-80% of registrations, during the period of active migration in the second half of autumn and winter it drops to about 40%. It is possible that many sightings of single birds also relate to twos or groups. Between October and December in both villages, migrating and wintering Bullfinches feed mainly on seeds of the Norway maple Acer platanoides , while from January to March they feed mainly on Sunflower Helianthus annuus seeds from the feeders. From October to January, Bullfinches would also often eat the seeds of other trees and shrubs (most commonly Rowan Sorbus aucuparia , Hawthorn Crataegus spp. , Lilac Syringa spp. ) and herbaceous plants (most often Common Nettle Urtica dioica and Common Mugwort Artemisia vulgaris ). In March and April, Bullfinches often pecked the buds of trees and bushes (most often Plum Prunus domestica , Blackthorn Prunus spinosa , Common Pear Pyrus communis , Lilac, Hawthorn and Apple Tree Malus domestica ) and Willow Salix spp . flowers. Regular foraging with Sunflower seeds from the feeders starts in December, about a month later than the appearance of this food source. This is most likely due to the appearance of groups of wintering Bullfinches at the observation sites, but may also be partly due to the fact that by January the stock of important seeds is depleted or becomes inaccessible due to snow.