Mass Migration of Social Voles ( Microtus socialis Pallas, 1773) in the Northwestern Caspian Region

摘要

A considerable increase in the social vole population distributed in the northwestern Caspian region (Republic of Kalmykia) in 2014–2016 has been recorded. The average long-term dominance index of the rodent cenosis in 2014–2016 was three times as high as in 2002–2010. The rise in the rodent population was caused by an increase in the reproduction rate due to adequate fodder supplies under favorable climatic conditions. In May 2016, social vole mass migration and deaths were registered; it is a rare phenomenon arising in rodents that may be caused by overdensity of their population. All of the males were first involved in the migration process because of increased intraspecific competition, higher aggression levels, and weaker attachment to the habitats as compared to the females. The mass migration and deaths of social voles in the northwestern Caspian region may reflect the unstable equilibrium dynamics caused by changes in the anthropogenic pressure and land-use system, which interacts with the damping effects in the climate.