Rapid decline of an isolated population of the black grouse Tetrao tetrix: the crisis at the southern limit of the range

Over the last century, the numbers and range of black grouse Tetrao tetrix have declined dramatically over most of Europe. The Central-European population is at present divided into small, isolated subpopulations, and Orawa (Carpathians, Poland-Slovakia) was considered until recently to be the most abundant one in the region. In 2002, it was estimated at 146–152 males. Surveys conducted in 2011–2014 showed that only 30–40 males were still present in this region. The total disappearance of leks (13 of 24 known leks have been abandoned) and the decline in overall numbers of males at existing leks (some leks were used by single males only) were recorded. In consequences, the number of lekking males decline by 76 % between 2002 and 2014. The nearest neighbour distance between active leks did not change, but the contraction of the total area used by the population (from 187.3 km2 in 2002 to 71.5 km2 in 2014) was recorded. The disappearance of leks was related to the size of the nearest peat bog; leks located close to small peat bogs were abandoned, while those located close to the larger ones remained active. Along with the decline in the numbers of lekking birds and the shrinkage of the range, a decrease in the size of wintering flocks was noted. This rapid fall over a short period of time in the number of black grouse and in the area used by the region’s largest population is indicative of a real threat of extinction of isolated populations. Rapid extinction risk should be taken into consideration when planning conservation measures applicable to its entire range of distribution.