The influence of grazing intensity and wetland availability on breeding shorebird populations in a Eurasian steppe

Traditional grazing has a long history on the steppes of Eurasia, dating back to as early as the Late Stone Age, which has contributed to present landscape composition and habitat topology. However, the number of livestock grazing in the steppes has significantly reduced during the past four decades. This exerted multiple detrimental effects in protected areas, by accelerating succession processes and leading to the declining quality of natural grassland habitats. This might have contributed to the global decline of shorebird populations that led even to local extinctions in a number of species. Here we aimed to investigate relationships among attributes of grazing and breeding population of shorebirds applying standardised surveys at ten sample sites in Hortobágy, the largest interconnected alkali steppe of Europe. We found that grazing pressure showed positive relationships with population sizes of nearly all shorebirds species. The number of breeding pairs increased with the density of grazing livestock. While only 15 % of waders bred in areas with less than 1,0 grazing unit/ha, this ratio amounted to 71 % in areas exceeding 1,5 grazing unit/ha. In several species, we found positive relationships between the number of breeding pairs and the size of open water surface. 81 % of breeding populations bred in sample sites where the extent of open water exceeded 10 ha. These findings support the hypothesis that grazing is a key driver of breeding in shorebirds in grassland ecosystems.