From 1983–2001, nest and chick losses in capercaillie and hazel grouse were studied in the mountains of Central Slovakia (Veľká Fatra Mts, Malá Fatra Mts, Kremnické vrchy Mts, Starohorské vrchy Mts, and Nízke Tatry Mts, 18°50’–19°10’E; 48°47’–49°19’N). Out of 75 capercaillie clutches 49 (65%) were destroyed. Out of 159 hazel grouse clutches 104 (65%) were destroyed. The main mammalian egg predators were stone marten (Martes foina), pine marten (Martes martes), mustelids (Mustela sp.), and red fox (Vulpes vulpes) (altogether 22%), wild boar (Sus scrofa) (9%), and brown bear (Ursus arctos) (3%). The predation pressure on capercaillie and hazel grouse nests decreased significantly during the incubation period (74% nest losses during the first half of May, 54% in the second half of May). Nest losses in both capercaillie and hazel grouse followed the fluctuation in small rodents, with lowest losses during peak year (57%) and highest losses during crash year (82%) and prepeak year (80%). Average number of capercaillie chicks accompanying a hen in June significantly decreased during the study period (5.0 in 1983, 2.6 in 2001). In contrast, in hazel grouse, no significant decrease in number of chicks per hen in June was recorded during the study period.