Семенов-Тян-Шанский О.И. Экология тетеревиных птиц. Москва, 1959.

Blackgame and Hazel grouse (0,53); snow cover interferes less with willow grouse feeding; it forages on birch and willow twigs 0,38 of year only. Rock ptarmigan gets berries and evergreen leaves all win­ ter long on hillocks, wind swept of snow. Ch. V deals with digestion-tract structure und function, including also dependence of grouse activity upon day light. Seasonal changes of grit contents in gizzards are discussed. The absence of vesica fellea and extraordinary size of coeca are the principal anatomic characters of Tetraonids (table 34). Size of heart in various Tetraonids greatly differs, being the least in Hazel grouse (5o/00 of body-weight) and the greatest in Rock ptarmigan (20o/00). In Capercaillie and Blackgame the heart is comparatively larger in females and smaller in males. In Ch. VI growth of juveniles and seasonal changes in weight of adult birds are described. Weight growth of young birds ceases with the change of their diet to winter ligneous food. Weight of immatuie Capercaillie females the first winter is about 90—91 % of that of adult females; weight of immature males does not exceed 73—76% of that of adult males (table 39); thus the growth of Capercaillie continues next summers (table 40 and fig. 49). Weight of Willow grouse and Rock ptarmigan hens (and probably other hens also) rises in time of mating and egg-laying, but decreases when they raise chickens. Weight of males reaches its maximum in XII-I and minimum in VI—VII (table 42). Weight of gizzard muscles changes in the course of year most of all: the difference makes about 20% in Capercaillie and 40% in Willow grouse; size of liver changes likewise (table 44). In Ch. VII moulting and methods of age determination of Tetraonids are considered. Aging of juveniles can be carried out by their body- weight or by the state of primaries moulting. Immature Capercaillie and Blackgame males can be distinguished from adults by their tails being shorter. The best method for aging both males and females is by the two outermost primary feathers: tips of these primaries are pointed and speckled in immature birds, but rounded and coloured uniformly with others in adults (fig. 58 and 59). S. Kirikov proposed a method for the estimation of the age of Capercaillies by a definite order in effacing certain fissures in cranium; this method is effectual up to 4 or 5 years in males and 3 years in females (pp. 171— 173, fig. 60—68). Ch. VIII — Parasites of Tetraonids. Frequency of occurrence of cestodes (Raillietina sp.) and ascarides (Ascaridia sp.) is subject to distinct seasonal changes (table 49, fig. 69—70). In general, Willow grouse are intensely invaded with these gelminths; Hazel grouse and Rock ptarmigan — least of all (table 50). Ch. IX considers predators and their activity. In both Reserves the stock of Tetraonids amounts to 26—42 kg for I sq. km approximately; being the largest forest birds, they make the bulk of total birds-mass. In northern forests only voles (mainly Clethrionomys sp.) and deer (elk and reindeer) are comparable with Tetraonids in their capacity as 302