Endangered birds of old growth forests in the Pirin National Park, SW Bulgaria: habitat preferrences, distribution and population sizes in 2001-2019

Actual status, distribution, numbers and threats for four forest bird species – Tengmalm’s Owl (Aegolius funereus), Pygmy Owl (Glaucidium passerinum), Three-toed Woodpecker (Picoides tridactylus), and Capercaillie (Tetrao urogallus) were studied in the territory of the Pirin National Park, Bulgaria, in the years 2001-2002 and 2019. For the owls, we used night line transect, 2-5 km in length, with acoustic imitation of species calls (henceforth playback) at each 500 (700) m (38 points in 2001-2002, 80 points in 2019). Daytime line transects, 2-5 km in length, were used for counting woodpeckers and Pygmy Owl. In Capercaillie counts, we searched for tracks in the snow, excrements or feathers. GIS analyses were applied for visualization of habitat association and distribution patterns of the studied species. The numbers and distribution of these species were compared between the two study periods and with existing data from previous studies. In 2019 a total of 29 occupied territories of Tengmalm’s Owls, 20 territories of Pygmy Owls, 2 territories of Three-toed Woodpeckers and 16 leks of Capercaillies were found. Decrease in numbers was detected for Tengmalm’s Owl (-30.4%) and Capercaillie. These species showed also different spatial pattern of presence between the two study periods. Threetoed Woodpecker population in Pirin NP is very small, not exceeding 10-15 pairs. Pygmy Owl was recorded for the first time during the breeding period in the National Park. The reasons for the differences between the two study periods were discussed. The results indicate some threats (ski tourism development, disturbance by people, sanitary cuttings, etc.) for these birds and can be used for improving the spatial planning of human activities in Pirin NP.