Ábrahám Levente (szerk.): Válogatott tanulmányok VI. - Natura Somogyiensis 19. (Kaposvár, 2010)
KOVÁCS GY., WINKLER D. & FARAGÓ S.: A kárókatona fészekalj és tojásméret vizsgálata a Kis-Balatonon és a Nagyberekben
264 NATURA SOMOGYIENSIS solely on the hydrobiology of the area; while research examining the natural treasures of the reservoir such as its fauna has largely been non-existent. Some occasional faunistical observations were made but these findings were never published while long-term monitoring researches were not conducted at all. This paper presents the results of a yearlong long study in the study area. Material and Methods Study area The Marcali reservoir, located 10 km from the southern shore of Lake Balaton and 3 km from the city Marcali, was constructed in 1983. Its main function is to store the nutrient elements and alluvium coming from the catchment. Along with other reservoirs, the Marcali reservoir maintains the steady water supply of Lake Balaton. In addition to these functions, the Marcali reservoir also plays an important role in sewage storage and biological water cleaning. Apart from the apparent fish farming utilization, hunting utilization is also significant with a yearly harvest of 500-1000 waterfowl bag. The influent streams are the Sári and Boronkai streams, while the effluent water arrives to Lake Balaton through the „Nyugati-övcsatorna" canal. The Marcali reservoir covers 400 ha with an average depth of 2 m. It is a typical barrage lake which consists of multiple sections. The surface area of the anterior settling ponds are 27 and 29 hectares, respectively, with average depths of 0.4-0.8 m. On the Eastern side two posterior settling ponds of 8 and 4 hectares can be found with an average depth of 0.5 m (DOBRAI 1985). The Marcali reservoir is located within the area of the Danube-Dráva National Park; it is part of the EU Natura 2000 Network as Special Protection Area (SPA) and Important Bird Areas (IBA). Survey methods Bird surveys were carried out from April 2007 to March 2008 (for a total of 19 field days). This research examines and analyses the data set of a yearlong long study period. The survey method used corresponds to the internationally approved waterbird counting technique. Surveys were conducted mostly biweekly and sometimes monthly due to hunting and other activities in the area. Considering the size and shape of the reservoir, four survey points were set out (Fig. 1) to ensure proper observability due to the relatively long distances. Round counts ( KAUPINNEN et al. 1991) were carried out during the morning hours, starting at the southern part of the reservoir at 7.30 am. Bird census continued from the points of the western, northern and lastly from the eastern survey points. Observations were made by the aid of a 10x50 binocular and a 30x monocular spotting scope. The applied survey method was suitable to detect the species of Gaviiformes, Podicipediformes, Pelecaniformes, Anseriformes, Ciconiiformes and Charadriiformes. Data analysis Breeding population was estimated by providing a minimum and a maximum value for the breeding pairs. The minimum value, which provides a minimum accurate estimate of population size, is based on the count of pairs observed during breeding season with or without young birds. The maximum value reflects the total number of individuals observed of a certain species.
