Fészkelő madárfajok az Osli-hanyban 2013-2022 között
Authors: Győrig Előd , Tatai Sándor , Pellinger Attila 
Published: July 2024

Nesting bird species in Osli-Hany between 2013-2022. Before the drainage of the entire area, Hanság – based on the descriptions of travellers – was a huge swampland with a rich avifauna (FATIO, 1891). Before the habitat reconstruction, the area was predominantly covered with grassland mainly cultivated by mowing, and to a lesser extent with woodland patches. Before the flooding of the area, surface water coverage was absent except for the transitional period following the melting of the winter precipitation, therefore unsuitable for the nesting water birds (SIPOS, 2007). Habitat reconstruction resulted in the colonization by many species, and Osli-Hany became a very important habitat, especially for water birds. As previously shown, fewer species with higher numbers nested in the first years after reconstruction, compared to later years (ARADI & GŐRI, 1997; KOVÁCS, 2010). In ten years, 108 species have been documented to breed, another 15 species potentially breed in Osli-Hany, which is a very high number in such a small area. Presumably, the primary source populations of the inhabitant water bird species are located at Fertő Lake, a Nyirkai-Hany, and lakes of Tóköz, data from the recapture and tracking of marked individuals, as well as the temporal population decrease on these lakes support this hypothesis (PELLINGER & FERENCZI, 2012). Several rare endangered species nest in the area, such as the strictly protected eastern Imperial Eagle (Aquila heliaca), White-tailed Eagle (Haliaetus albicilla) and Pygmy Cormorant (Microcarbo pygmeus). Black-necked Grebe (Podiceps nigricollis), Garganey (Spatula querquedula) and Avocet (Recurvirostra avosetta) only nested in the first few years after wetland restoration, and a significant decrease in the number of individuals was observed in case of the Black-winged Stilt (Himantopus himantopus) and the Eurasian Coot (Fulica atra). The initial aim of the monitoring started in 2013 was faunistic data collection without a specific focus on gathering information about population trends. However, for some species, data on the size of the breeding population has been published as additional data, and systematic survey focusing on population trends has started from 2022. At the point counting surveys, the highest density and diversity were observed in forest habitat patches (GYŐRIG, 2022). In the spring of 2022, sedge dominated habitats were covered by 50-60 cm deep standing water, providing suitable nesting sites for more generalist species i. e. the Sedge Warbler (Acrocephalus schoenobaenus), Savi’s Warbler (Locustella luscinioides), Reed Bunting (Emberiza schoeniclus) and the Water Rail (Rallus aquaticus), reaching their highest density in that year. Despite the lower relative diversity of sedgelands, nesting water birds prefer such habitats over other grassland habitats, indicating the importance of the provision of water to these areas. Semi-open marshes with sparse emergent vegetation are also ideal breeding habitats for these 4 species that nested with slightly lower but similar density in those habitats. Consequently, flooded areas became an essential habitat not only for water birds, but some passerine species also prefer them as nesting sites. The Eurasian Coot (Fulica atra), a species that also likes flooded areas, reached its highest density here. The goal of habitat reconstructions is to induce the highest biodiversity possible, but due to the species’ different habitat needs, habitat management plans must be optimized especially regarding water conditions. Managing such an area is not an easy task, many factors can make it difficult to operate properly such as climatic changes, invasive species, and in the case of wetlands, water supply and water quality. In the case of Osli-Hany, the water level is affected by the level of Rábca river. The area consists of one big waterbody, making it impossible to regulate parts of the area separately (as in case of Nyirkai-Hany, which is divided into three “cassettes”). However, the northwestern corner of the area could be separated as the water flows to the east through a culvert. If a sluice were placed on this culvert, an 18.5-hectare big area could be managed separately from the rest. A part of the area which is a pasture grazed by domestic Water Buffalo could be flooded several times a year. Periodical drainage of this pasture area would be also necessary to maintain the optimal vegetation length by grazing and mowing. After reducing vegetation, the area could be flooded again for only a three-year period, therefore avoiding the stagnant areas of the wetland could be possible. In this way, species that prefer the first year’s post flooding would also have a regular nesting opportunity. There is no need for such an intervention in most of the area, as many occurrent species prefer stagnant areas. Nevertheless, water level fluctuations may be necessary to maintain adequate water quality and the lower organism community. Osli-Hany has good water quality (LUDÁNYI et al. 2020), for the maintenance it is advisable to adjust water levels according to the seasonal/climatic conditions. Due to the extra water supply at the end of winter, a higher water level would develop in accordance with the climate of the Hanság, which would continuously decrease from the end of May and remain at a lower level until winter or the following spring. A treatment proposal has been formulated to imitate these natural processes (KISS et al., 2020), which can result in the creation of more diverse vegetation structure due to the different water levels kept in balance (TIMMERMANN et al., 2006, TAKÁCS et al., 2007), which is also beneficial for bird fauna (GÁTI et al., 2000, FERENCZI et al., 2009). Our study may serve as a foundation for future monitoring of breeding passerine bird populations in the area as well as model for future wetland restoration plans. In the first 10 years, wetland restoration of the Osli-Hany resulted in breeding of 105 species including many strictly protected and endangered species. Systematic water management of the area with proper timing would be crucial to help the vegetation development of the area. Our future aim is to create even more diverse habitats which may increase the variety of breeding bird community.