Abstract: The relevance of long-term studies of biological communities is growing every year due to global climate change and anthropogenic transformations. Monitoring the numbers of common forest-dwelling bird species in Eurasia shows a decline, particularly among long-distance migratory, taiga, and mountain species. In the Caucasus, such studies are fragmented; therefore, any long-term data from this region are of great value. It is important to identify the causes of these changes and predict future events.

Our study aimed to determine the dynamics of bird populations in the main forest communities of the Caucasian State Nature Reserve (Russia). From 2006 to 2024, we conducted route censuses of birds in mid-mountain (600–1500 m a.s.l.) and high-mountain (1500–2000 m a.s.l.) beech-fir forests. The lengths of the routes were 304 km and 246 km, respectively. Fifty-nine bird species were identified, and population trends for 23 regularly occurring species were analysed. A significant downward trend was demonstrated for two dominant species, Periparus ater and Phylloscopus nitidus, and three common species, Sitta europaea, Turdus viscivorus, and Prunella modularis. No species demonstrated significant positive trends. The overall downward trend is not significant, but is clearly visible.

The decline in numbers is more intense in the upper mountain beech-fir forests. The density decreased from 422 individuals/km2 to 313 individuals/km2 (-25.8%); the occurrence decreased from 302 individuals/10 km to 185 individuals/10 km (-38.8%). Compared to the mid-mountain beech-fir forests, the density decreased from 480 individuals/km2 to 425 individuals/km2 (-12.5%); the occurrence decreased from 340 individuals/10 km to 240 individuals/10 km (-29.4%). A relationship was shown between the dynamics of the number of birds and the amount of precipitation, which has also decreased in recent years.

A relationship was revealed between the number of birds and temperature and the North Atlantic Oscillation index. It was shown that the number of sedentary bird species is more dependent on climatic factors than the number of nearby migrant species. The numbers of long-distance migrants (Phylloscopus nitidus, Sylvia atricapilla, and Ficedula parva) were found to be unrelated to the analysed climatic factors. A relationship between the number of birds and catastrophic weather events, such as late-spring snowfalls and frosts, is discussed.

Overall, the dynamic processes in the bird population of the Western Caucasus are more similar to those in Europe than to those in Asia, where bird populations are relatively more stable. It is predicted that with the transition from the arid to the humid phase and the absence of spring frosts and snowfalls, the number of birds in the Caucasian State Nature Reserve will increase again.

Perevozov A.G. 2026. Dynamics of the number of birds in beech-fir forests of the Caucasian State Nature Reserve (Western Caucasus) in connection with climatic factors. Nature Conservation Research 11(1): 13–27. https://dx.doi.org/10.24189/ncr.2026.003