Annual dynamics, nature-conservancy evaluation and an overview of data on the occurrence of waterbirds at Šaleška Lakes (N Slovenia)

Abstract Between September 2014 and August 2015, 32 systematic surveys of waterbirds were carried out in 10-day periods in the area of Šaleška Lakes. The main objectives of the surveys were to establish the birds’species structure and abundance as well as to assess the area’s significance for their breeding, migration and overwintering. A total of 8927 individuals belonging to 53 species were recorded. Most species were observed at the end of March (27), whereas the highest number of individuals were registered in early January (535). The lowest number of individuals were counted in May (73). Mallard Anas platyrhynchos, Great Crested Grebe Podiceps cristatus, Mute Swan Cygnus olor and Grey Heron Ardea cinerea were observed during all counts. An additional 10 species were registered in at least 50% of the 10-day periods. The highest number of individuals (2891) and species (34) were counted at Lake Šoštanj, the highest number of individuals (295) and species (21) in a single 10-day survey period at Lake Gaberke. Most nestlings and nesting species were recorded at Lake Velenje. The majority of species occurred on all lakes within the research area, while some of them frequented certain lakes only exceptionally. The lowest numbers of birds were observed in central parts of all major waterbodies, particularly at Lake Velenje. Distribution of waterbirds at Šaleška Lakes is greatly influenced by the presence and distribution of people along them, as well as by the depth and riparian vegetation of the lakes and number of suitable roosting places. The number of breeding species is higher than in the 1994-2003 period. Little Bittern Ixobrychus minutus, Kingfisher Alcedo atthis and Great Reed Warbler Acrocephalus arundinaceus are new breeders for the area. The most abundant breeder is the Mallard with up to 16 pairs. The area’s breeders of the greatest conservation concern are the Little Bittern, Great Reed Warbler and Reed Warbler Acrocephalus scirpaceus, with the latter boasting the greatest share of the national breeding population (5%) in the area. Generally, most species occur during the migration season, although none of them in the numbers of conservation concern. Among the 33 waterbird species observed during the International Waterbird Censuses, five were recorded in all 18 years. Pochard Aythya ferina and Coot Fulica atra are of the greatest conservation concern, whereas the greatest share of the national population is reached by the Coot and Great Crested Grebe. In spite of the fact that the numbers of overwintering waterbirds in Slovenia are increasing, their numbers are declining at Šaleška Lakes. Among the 13 species recorded during more than ten International Waterbird Counts in the area researched, eight species are experiencing negative trends.