Habitat characteristics assessmen of the wetlands with breeding Ferruginous Duck Aythya nyroca and Pochard A. ferina in Bulgaria / Ocena habitatnih značilnosti mokrišč z gnezdečimi kostanjevkami Aythya nyroca in sivkami A. ferina v Bolgariji

Abstract

Abstract The Ferruginous Duck Aythya nyroca and Pochard A. ferina are both regular breeders in Bulgaria. In the 19th and early 20th centuries, the Ferruginous Duck was a widely distributed and abundant breeding species in Bulgaria, while Pochard was first confirmed to breed in the country only in the 1950s. Breeding habitat characteristics of Ferruginous Duck and Pochard were assessed in 2002 during a national census of the former species in 30 and 23 wetlands, respectively, where the species were present. Preferred habitat characteristics were determined based on vegetation cover, water depth, and the presence of mosaic vegetation, bank side vegetation, floating vegetation, shallow or steep banks, shallow mudflats, shallow vegetated areas and woodland along the banks. In 2002, the Ferruginous Duck population in Bulgaria was restricted more to artificial wetlands, like fishponds and micro-reservoirs, while Pochard preferred more natural wetlands, predominantly natural marshes. The altitude of wetlands with Ferruginous Ducks varied markedly, with breeding recorded up to 880 m a.s.l., while Pochard bred at lower altitudes, mostly below 300 m a.s.l. Analysis revealed that Ferruginous Ducks preferred well-vegetated, comparatively shallow wetlands with well-structured mosaic vegetation and a diversity of microhabitats, like shallow mudflats and floating vegetation. The Pochard was found to be more of a generalist in wetland selection, significantly correlated with fewer wetland parameters, and showed preference only for larger, open-water bodies. These results could help explain and give some insight into the reasons for the differences in range size, numbers and distribution of the two species and their respective conservation status in Europe and worldwide. The Pochard, whilst close to the limits of the breeding range in Bulgaria, expands its range in Europe, occupying a variety of wetlands and thus having a favourable status. The Ferruginous Duck is more of a habitat specialist, which limits its distribution and makes it more susceptible to habitat changes. These habitat preferences and the deterioration of the wetland habitats in many parts of its range could probably explain the Ferruginous Duck decreasing population and shrinking breeding range, and thus its current unfavourable conservation status.