Collective roost of corvids in Melitopol (Zaporozhye region) in 2014–2015

The article contains the results of observations on the formation, existence and the dissociation of the collective winter roost of corvids (crow species) in 2014–2015 in Melitopol (Zaporozhye region). A detailed study of the concentration and the dynamics of its functioning during the winter period was carried out. By the method of absolute counting of birds, the estimation of the gathering process on the roost in the night and dispersal from roost in the morning was carried out twice a week (a total of 47 days of observation in the morning and evening). We selected the following essential parameters: time of the beginning and ending of the process of dispersal from the roost in the morning and gathering at the roost in the evening; time – study of birds’ flight activity in these intervals; the number and species composition of birds; directions of flights with their mapping; weather conditions. Within the city of Melitopol during the winter period of 2014–2015, corvids (Rook, Western Jackdaw, Eurasian Magpie and Common Raven) form one central roost. The total number of birds at the roost was typically 18 thousand individuals. The collective roost exists from the beginning of October till the end of March. The analysis of dynamics of the birds’ number during the existence of the collective showed a wide amplitude of fluctuation in the range of 1,000–5,000 individuals during autumn (10 times) and spring (5 times) migration. By the end of November migration ends, the number of birds has stabilized, and the location of the night roost becomes permanent. In winter the gathering is more stable and fluctuations in number lie within the limits of 500 individuals (8 times). The number of birds that roost collectively decreased from mid – March. In this article considerable attention is paid to processes of the birds’ dispersal from the roost site and gathering at the roost at night. The observations showed a high degree of dependence on day length and different intensity of these types of daily activity. During the analysis of the process of morning dispersal of birds from the collective roost, seasonal differences in the time of dispersal were found. In the winter months this period was significantly shorter than in the autumn and spring. The duration of dispersal of birds from the roost (28.4 ± 9 min; lim – 15–45 min) was reliably less than that of gathering at the roost (87.9 ± 14.8 min; lim – 30–115 min); the difference of averages is significant for the highest probability threshold of р ≥ 0.001 for the entire observation period. As a result of research on dispersal and gathering of birds at the roost site, the basic strategies of the birds’ behaviour were revealled. For morning dispersal of birds from the territory of the roost the strategy of “gathering with a pause” (16 registrations; 35.6%) is dominant. The strategy of “the damped wave” is sub dominant (14; 31.1%). The lowest percentage was taken up by the strategy of “three peaks” (1; 2.2%). For the evening gathering of birds at the roost, the strategy of “two peaks” is dominant. The lowest percentage was taken up by the strategy of “gathering with a pause” (2; 4.5%). The overall species diversity within a gathering and on the routes of birds’ flights reached 24 species. The undisputed dominant in numbers was the Rook, and the subdominan was the Jackdaw. Thus, corvids form the basis of the ornithological complex of the forest – park zone of Melitopol in the autumn and spring period.