Why the capercaillie population (Tetrao urogallus L.) in mountain forests in the Central Slovakia decline?

Abstract

From 1981–2010, population dynamics of the capercaillie Tetrao urogallus L. was studied on forty-three leks in the Western Carpathians (Slovakia). Nest and chick losses were also studied. Altogether, 94 nests with clutches, 124 hens with chicks in June and 132 in the period between 1 st August and 15 th September were checked. Results demonstrate a marked decrease (>50%) in numbers of cocks and hens on twelve monitored leks (28%) and a slight decrease (<50%) on ten display grounds (24%). During the study period, capercaillie cocks became extinct on eleven (25%) leks and in their surroundings. More or less constant numbers were found on only eight leks (19%) and a slight increase occurred on only 2 leks (4%). The mean number of juveniles per a hen was 1.9 over the whole study. The average number of chicks accompanying a hen significantly decreased during the study period. Female chicks were consistently outnumbering male chicks. Predation appeared to be of major importance in limiting numbers of capercaillie chicks. Out of 94 capercaillie clutches 59 (63%) were destroyed. Predaceous pressure on chicks was high in spite of the fact that with progressing breeding season, the food offer for predators was continually increasing.