Long-Term Trends of Hazel Grouse (Tetrastes bonasia) in the Bohemian Forest (Šumava), Czech Republic, 1972-2019

The population dynamics of Hazel Grouse were studied by presence/absence recording at stationary sites along fixed routes (110 km) in the central part of Sumava (Bohemian Forest, Czech Republic) from 1972 to 2019. The 100 km(2) study area covered altitudes between 600 m (Rejstejn) and 1253 m above sea level (Mt. Sokol). Our database contained indices of Hazel Grouse occupancy: positive sites/visited sites for a yearly increasing number of Hazel Grouse occurrence sites (n = 134) for 48 years. We used a loglinear Poisson regression method to analyze the long-term population trend for Hazel Grouse in the study area. In the period from 1972 to 2006 we found a stable Hazel Grouse population (p = 0.83). From 2006-2007 to 2019, the population index dropped (-3.8% per year, p < 0.05). This decline is assumed to be influenced by habitat loss due to succession, resulting in older, more open forest stands, by strongly increasing forestry and windstorm "Kyrill", followed by clear cutting, bark beetle damage, and the removal of pioneer trees in spruce plantations, which diminished buds and catkins, the dominant winter food of Hazel Grouse. The influence of disturbance by increasing tourist activities and/or predation is also discussed. Our results could help to optimize the conservation efforts for Hazel Grouse in the Bohemian Forest.