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

brooding, partly when brooding hens abandon their nests in cold or rainy weather. Ch. XI — Counts and population fluctuations. In tabl. 80—81 are cited census figures of Tetraonids for 1 sq. km, and in tabl. 82—83— counts for 100-hours trip. In tabl. 84—87 «peak»-years and depression- years of Tetraonids in Scandinavian countries and USSR are compa­ red. Sometimes, as in 1932, 1935, 1937, 1939 and 1953, peak years or low years spread on immense space of forest region, from Norway to Ural. Population fluctuations are the result of interaction of two changeable factors — success of breeding and rate of mortality. When the meaning of separate meteorological factors in population fluctua­ tions must be revealed, census figures are but of little use; age ratios in population (table 88) make better index for such studies. Correlation months or 10-days periods and ratios of immature birds in Capercaillie coefficients between air temperatures (or precipitation sums) for populations are listed in table 89. In Lapalnd Reserve best results are received with the mean temperature of June (r = + 0 , 6 7 + 0,15), with first 10 days of June (r = -(- 0,71 + 0 ,1 3 ) , with the coldest 10-days period of June (r = + 0,74 + 0,12) and minimum temperature in June (r = + 0,82 + 0,09). In Petshora-Ylytsh Reserve — with precipitation sum in June (r = — 0,96 + 0,03), with mean temperature in 10 last days of May (r = + 0 , 8 0 + 0,15) and with the coldest of 3 ten-days periods of incubation (r = + 0 , 8 5 + 0,11). Thus the close connection of breeding success in Capercaillie with weather conditions in brooding time is well demonstrated. In table 92 the age composition of Capercaillie populations in both Reserves is calculated. For age determination two methods were used, immature birds were distinguished by pinion tips or tail length, the age of adults was estimated by cranium fissures. The survival rate in the first winter and second summer of life is about 4(6.% near Lapland, •and 33% near Petshora-Ylytsh Reserves; in each of further years — about 59% and 54% correspondingly. Thus the mortality rate for adult Capercaillies is about 70—75% of that of yearlings. The age composi­ tion in Capercaillie cocks shot on mating grounds is quite remarkable. In table 93 the number of Capercaillies shot in open season and on mating grounds, c'onsidernig their age, is recorded and the figures are compared (see also fig. 97). On mating grounds 1- and even 2- years-old cocks are suppressed in display by males of three years and older; for this reason elder birds prevail in the bag. In Ch. XII migrations of Tetraonids are discussed. Marking records suggest that forest species of Tetraonids are almost stationary birds: about 58% of marked birds were recorded not farther than 2,5 km (or 1,5 miles) from the point of marking and none farther than 40 km. Willow grouse and Rock ptarmigans of tundra regions pass winter by the northern timber-line and their migrations reach some hundreds kilometers; in fluctuation studies of these birds, migrations should be taken into consideration. 304