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

«key-industry» (table 54). Lists of birds of prey with data of their food composition are recorded in tabl. 55—57; analogous in tabl. 60—61 for beasts of prey. Fig 74—75 demonstrate, how the role of Tetraonids in marten’s diet differs from year to year, according to accesibility of voles, constituting their principal food item. In winter martens (as well as foxes) often get eggs of Tetraonids from under the snow. These eggs are the result of embryonic mortality in course of brooding; for this reason their occurrence in winter diet depends upon the age ratio of Capercaillie population, and, on the other hand, upon the accessibility of voles (fig. 76). Ch. X — Breeding habits. Brooding regime studies with actographs of original construction (fig. 81—83) are considered here. Registered by actographs brooding regimes of Capercaillie (fig. 84, 85), Blackgame (fig. 88), Hazel grouse (fig. 89) and Willow grouse (fig. 91) are partly represented graphically. Egg-laying in Capercaillie and Hazel grouse daily takes place later and then, after passing one day, the new cycle begins in the morning (fig. 85, 89). Brooding begins in the evening* before the last egg is laid. On the first day of brooding the hen leaves nest more frequenty and for a longer time than later. While chick- hatching, during about 23—37 hours, the brooding hen does not abandon her nest at all. Going from the nest away, the covey makes only 7— 14 m in an hour. Brooding regime can be characterized as follows: C ap ercaillie B lack - grou se P etsh . H a zel grouse P e tsh . W illow grouse Lapl. Lapl. P etsh . Duration of incubation * , days . .• 26 2 5 - 2 6 > 2 3 2 5 ,4 > 1 8 Ordinary numb, of walks, in a day . 2 - 3 2 - 3 2 - 3 3 - 4 3 - 5 Duration of each walk, min...................... 2 0 - 4 0 1 0 - 2 5 1 0 - 2 5 15—25 1 0 - 3 0 Complete dur. of walks, part of a day 0,0 6 1 0 ,0 2 7 0 ,0 3 2 0 ,0 4 9 0 ,0 4 5 E g g turnings, in a day . . i . . 26 2 2 - 3 2 25 33 ? Air temp, of incub. period, av. . . . 9 ,0 ° 1 0 ,2 ° 9 ,5 ° 1 0 ,9 ° 10,1 ° „ at time of hens absence . 8 ,7 ° 8 ,9 ° 7 ,8 ° 1 1 ,4 ° 9 ,2 ° Minim, temp. „ „ „ . . 0 ,9 ° - 5 , 5 ° - 2 , 0 ° 0 ,3 ° - 0 , 9 ° Time of abs., when hen is driv., hours 1 - 3 1—3 1 - 3 ? 1 Max. tim e of absence, hours . . . . 7 , 5 6, 3 (40)** 0 ,8 1 ,4 Time on nest, when chicks hatch., hours ............................................................. 34 2 3 - 3 4 18 37 34 Number of n ests s t u d i e d ........................ 1 5 2 1 2 * From beginning of brooding up to departure of the covey. ** Perhaips the e g g s w ere frozen (nest later destroyed). The eggs of Tetraonids can not be frozen during the absence of brooding female, because their cooling is a comparatively slow process. Losses of eggs in cold springs take place partly if they freeze before