Breeding Success of Eurasian Cranes (Grus grus, Gruiformes, Aves) in Conditions of Changing Environment: Effect of Climatic and Hydrometeorological Trends

Predictions often suggest that changes in the conditions caused by climate warming will have negative consequences for the population dynamics of many bird species, but clear evidence of this is rarely provided. Changes in bird migration and nesting periods and the physical state of nesting individuals were established for a long list of species in most regions of the Northern Hemisphere; however, data on the consequences (first of all, breeding productivity) are still insufficient for the conclusions. Monitoring the age structure of autumn premigratory gatherings of Eurasian cranes in the northern part of Moscow Region demonstrated that despite climate warming in the region, the percentage of young individuals did not change over a 30-year period. The number of juveniles is associated positively with the temperature of the breeding season and negatively with the amount of precipitation. In warmer seasons, the breeding success of Eurasian cranes was higher, while it decreased in the seasons with a lot of precipitation. Thus, the breeding success in a given species is controlled by two parameters, including the amount of precipitation and the air temperature during the breeding season. At the same time, significant trends in the long-term dynamics of both these parameters are absent. The highest percentage of juveniles was registered in years with a combination of high air temperatures and a low amount of precipitation. An increase in precipitation and colder conditions during the breeding period lead to a reduction in the percentage of juveniles in the premigratory gatherings. A combination of low temperatures and large amount of precipitation was the most unfavorable combination for the Eurasian cranes; in such years, the percentage of juveniles was minimal.