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

KOVÁCS GY., NAGY Á. & WINKLER D.: WATERFOWL POPULATION SURVEY 271 Table 5: Comparison of Shannon diversities (t-values, **P=0.01; *P=0.05) t Summer Autumn Winter Early spring Spring 4.4738** 2.7195** 17.501** 2.9135** Summer 2.9427** 31.5140** 9.5445** Autumn 33.5150** 7.9096** Winter 18.9540** airs confirmed the results of the Hutcheson probe and showed markedly and significant differences between diversities. It can also be observed that the diversity profiles of the early spring and spring communities are very close to each other (Fig. 11). Bird community response to water level changes Results show that the effect of water level alteration to bird community structure is not indifferent and species richness positively correlated with increased water levels (R

2=0.66, pO.OOl) (Fig. 12). Very low water levels was detected from October to February. While species richness was average at medium-low water levels during the frostless period, it significantly decreased in the frost period starting in November. Similar trend can be observed in relation to the correlation of water levels and the number of individuals of diving duck species. At higher water levels more individuals of Aythya species were observed (R

2=0.62, p<0.01) (Fig. 13). Regarding the Mute Swan (Fig. 14) and shorebirds (Fig. 15), the relationship was just the opposite. The number of individuals of Mute Swan and shorebird species was negatively correlated with water levels (R

2=0.49, p<0.01 and R

2=0.87, pO.OOl, respectively). The diet of mute swans consists mostly of submerged aquatic vegetation. The optimal diving depth is up to 1 m. The shore gradient of the reservoir on reedless parts are discontinuous, it deepens abruptly; therefore, this zone can only be optimally used for feeding at low or medium water levels. In regards to shorebirds, the strong negative correlation of their numbers with water levels can be explained with their feeding habits, since they prefer feeding areas which include shallow water depths of up to three inches. Fig. 11: Diversity profiles of bird communities