Additional data on the summer-autumn diet of the Black grouse (Lyrurus tetrix, Galliformes, Tetraonidae) in the southern forest zone of the Russian Plain

The composition of the summer-autumn diet of the Black grouse (Lyrurus tetrix) in the south of the forest zone ranging from Poland to the Urals has been thoroughly studied, but questions about the actual ratios of food consumed remain open. The feeding strategy of the birds in late summer and early autumn is also unknown. To partially fill in these gaps, we analyzed the craw contents of the birds hunted in the southern taiga (n = 22) and in coniferous-broadleaf forests (n = 24) in July–October 1987–2023. The plant genera Trifolium, Hieracium, Rumex, Sonchus and other herbs growing in a grassland or at forest edges formed the main part of the diet (% wet weight) in both black grouse populations studied. The basis of animal food was also represented by insects of open landscapes: grasshoppers (Acrididae) and leaf beetles (Chrysomelidae). The main diet components (75–76% wet weight) constituted only ~20% of the total food lists, indicating something close to oligophagy: long food lists with only a few food items being important and most food species found to be consumed in very small quantities. The relations between the estimates of wet weight (%) and the occurrence of food were expectedly weak, but large weights could correspond to either low or high occurrence estimates; this situation should make comparisons across literary sources difficult. The total absence of any fragments of heather shrubs (Ericaceae) in the diet of both populations along with the absence of any berries in the nutrition of the southern taiga individuals were unexpected. In contrast to other L. tetrix populations from the southern forests of the Russian Plain, the attention the study birds paid to food objects proved to be dispersed across many food species, possibly owing to the long time span of our datasets. Nevertheless, the most probable reason for all habits of the Black grouse noted seems to lie in a decreased human agricultural activity (grain growing and haymaking) and ousting the birds from forest-meadow edges by people (via recreation and gathering berries and mushrooms) deep inside grassland habitats, where the forage base for black grouses has apparently been much more variable and less predictable than under the discontinuous forest canopy more familiar to the birds.