Long-Term Monitoring of the Numbers of Forest Rodents in Ilmeny Reserve

—In the birch–pine forests of Ilmeny Reserve the bank vole is predominant in numbers, with the pygmy wood mouse being in second place. The results of our monitoring of the numbers of these rodents for 27 years (1991–2018) are presented. A total of 1610 rodents were caught, of which the bank vole accounted for 52.6%; the pygmy wood mouse, for 32%; and other species, for 15.4%. The autumn abundance of the bank vole was 4.6 ± 1.8 and 18.9 ± 2.6 ind./100 trap-days for 1991–1999 and 2000–2018, respectively; that of the pygmy wood mouse was 2.1 ± 1.9 and 18.9 ± 2.6 ind./100 trap-days, respectively. Since 2000, the peak amplitude of the bank vole numbers has increased by 1.1–2.5 times, and that of the pygmy wood mouse has increased by 2.5–4.2 times. Since 2006, the number peaks of these rodents began to repeat every 2–3 years. Over eighteen years (2000–2018), the autumn abundance of the bank vole twice (2008 and 2017) reached its peak values, at which the reproduction of voles ceased as early as July or the beginning of August. The correlation coefficient of the autumn abundance of the bank vole and pygmy wood mouse for 1996–2018 was 0.64 ± 0.1. The spring abundance of the pygmy wood mouse has begun more often to exceed the spring abundance of the bank vole. Changes in the amplitude and abundance waves of the bank vole and pygmy wood mouse are obviously associated with some climatic features of the recent decades.