Long-term migratory changes in Grus grus (Gruiformes, Aves) arrival and departure on breeding grounds in Central Russia

Climate change exerts a substantial influence on ecological processes, particularly affecting the timing of bird migration. One of the most visible impacts is the shifting of both arrival and departure dates for migratory birds. These changes are not isolated events but are part of broader patterns that have been observed over time. Long-term studies are essential for identifying these trends, as they provide the data needed to evaluate how various climatic factors shape the behaviour of migratory species. In this study, data have been collected over many decades from three Protected Areas in the centre of European Russia (Moscow Region, Ryazan Region, and Republic of Mordovia) and analysed to assess the long-term migratory shifts in Grus grus (hereinafter – Eurasian crane). Compared to the Mordovia State Nature Reserve (τ = -0.10, p = 0.43), spring arrival of Eurasian cranes shifted to earlier dates in the Crane Homeland Sanctuary (τ = -0.32, p < 0.05) and Oka State Nature Reserve (τ = -0.35, p < 0.05). Similarly, departure dates from breeding grounds shifted to later in the Crane Homeland Sanctuary (τ = 0.56, p < 0.05) and Oka State Nature Reserve (τ = 0.28, p < 0.05), but not in the Mordovia State Nature Reserve (τ = 0.09, p = 0.37). At the same time, the arrival dates in Oka State Nature Reserve were earlier, and the departure dates were later compared to the other two Protected Areas. Changes in their arrival have started happening earlier than in their departure. We evaluated the species' responses to temperature, precipitation, and other factors that influence its migratory behaviour. The analysis was conducted using Boosted Regression Trees, which allows us determining the relative contribution of each factor to explain the variability in migration timing. Earlier arrival is associated with climate warming, i.e. an increase in winter and early spring temperatures. The sum of temperatures from 01 March to the arrival date (47.7%) had the highest influence on the timing of arrival. Notably, the precipitation has a higher influence on Eurasian crane departure, but temperature has more influence on their arrival. The amount of precipitation in September (10.3%) had an influence on the timing of departure comparable to that of the average temperature in August (12%). The staying time of Eurasian crane in the breeding areas has also increased. Despite regional differences, trends in migratory changes in all three regions are moving in a similar direction.