The Chronicles of Nature (Letopis Prirody) kept in the nature reserves of the Russian Federaton aggregate a wide spectrum of systematic field records. Information of particular interest therein is the timing of ripening of berries and their yields across years, since berries are an important food for many wildlife species, including brown bear (Ursus arctos), a core species in boreal European Russia. Such trophic links are most explicit and interesting in the autumn during fattening or hyperphagia period in bears, when the animals depend on berry availability for storing up fat. We aimed to identify the ecological relationships of brown bear applying integrated analysis of field data on the carnivore diet and of records from the Chronicles of Nature of the Kivach Nature Reserves (the middle taiga) and the Pinega Nature Reserve (the northern taiga). We have determined the prevalence (%) of the certain foods in brown bear scats sampled from transects along forest roads and paths. The number and productivity of fruit-bearing rowan trees (Sorbus aucuparia) were determined along permanent transects. Bilberry (Vaccinium myrtillus) and cowberry (Vaccinium vitis-idaea) berries dominate in brown bear diet. Berry ripening dates (19–43 days) and the average yield (scores 1.3 to 5.0) vary greatly over years. Trends in ripening onset dates follow a vector towards earlier dates. In the Pinega NR, the rate of this process is faster in bilberry. The coefficient of rank correlation between the number of fruit- bearing rowans along dirt roads and rowan prevalence in scats was r = 1. The same significant correlation was found between the number of fruit-bearing rowan trees and rowan berry yield. The prevalence of different foods in brown bear scats during the hyperphagia period shows the high dietary plasticity of species. A reliable strong correlation was detected in the Pinega NR between the last sighting of brown bear tracks in autumn and the onset of berry ripening in bog bilberry and rowan. The relatively stable food supply for brown bear in the middle and northern taiga of European Russia is one of the factors defining the high numbers and wide distribution of the species.

Keywords: Chronicles of Nature, nature reserves, middle and northern taiga subzones, fattening foods, berry fruiting, trophic links, dietary plasticity, Ursus arctos