Ábrahám Levente (szerk.): Válogatott tanulmányok V. - Natura Somogyiensis 17. (Kaposvár, 2010)
LANSZKI, J., MÓROCZ, A. & CONROY, J. W. H.: A vidra (Lutra lutra) kora tavaszi táplálék-összetétele a Gemenci Tájegység (Duna-Dráva Nemzeti Park, Magyarország) természetes élőhelyein
LANSZKI, J., MÓROCZ, A. & CONROY, J. W. H.: DIET OF EURASIAN OTTERS 321 a) 100% i Ej 75% i S 50% v-i i 25% .2 pq 0% Fishougin: • Exotic • Native ID HS HKDD ND BD Asa HS ND B P — 1 TD HK DD Relative distance 5 10 15 20 25 Fig. 5: Distribution of fish origin categories in the diet of otters (a) and dendogram of diet similarity (b) in the Gemenc Area, Hungary. For locations and other explanation see Fig. 1 and Fig. 2. Hydrous piceus ), molluscs (zebra mussel Dreissena polymorpha in TD, and snail Cepaea spp. on BD) were rare and consumed in low quantities. Reptiles, birds and mammals were not detected in the spraint samples. The low trophic niche values (Table 2) showed high specialization in fish. Although the principal fish prey indicates that fish availability might be satisfactory for otters, fish survey by electrofishing indicated relatively low fish densities (Z. Sallai unpubl. data). According to KRANZ (2000), fish availability does not fluctuate as strongly as on the fish ponds as on rivers. High winter and spring fish consumption was found on fish ponds and water reservoirs, as well as on the rivers and oxbow lakes of Hungary which are abundant in fish (KEMENES & NECHAY 1990, review: LANSZKI 2009). When the availability of fish is low or the ability of otters to catch fish is restrained, e.g., during the cold period, otters switch to 'buffer' foods (review: CHANIN 1985, MASON & MACDONALD 1986, CARSS 1995, KRUUK 1995, JEDRZEJEWSKA et al. 2001, CLAVERO et al. 2003). However, spring is also the main period of spawning of amphibians, and in numerous studies frogs and toads are important buffer preys for otters (WEBER 1990, DELIBES et al. 2000, review for Hungary: LANSZKI 2009), but the importance of these (and all non-fish food types) was generally low during the period of study - the early spring period. On the basis of hierarchical cluster analysis (Fig. 2b), three separate groups were identified. Those locations (from top to bottom on the dendogram) where fish consumption was high (around 100%) fell into one group, those where consumption of amphibians was in higher ratios (3.9-6.3%) into the second, while at Taplósi Holt-Duna (TD), where consumption of amphibians and crayfish was considerable, fell into the third group. A significant area-dependent difference was found in the distribution of fish weights (Chi-Square test, x 2is = 57.88, P0.001). However, the fish consumed by otters were small sized (<100 g) [in all areas above 50% ](Fig. 3a), but in three areas (TD, HS, HK, first cluster on Fig. 3b) consumption of these was determinant, while on the other three areas (DD, ND, BD, second cluster on Fig. 3b) consumption of 100-500 g fish was also considerable (min-max 35.1-43.5%). Specimens weighing more than 1000 g were rarely taken by otters, consumed only on TD (9.6%), DD (1.7%) and BD (3.5%). Otters living by oxbow lakes near to the Danube River consumed mostly small lightweight fish. These results are similar to those from studies at other similar locations, other oxbow lakes and river sections, along the Drava and large rivers in Hungary (LANSZKI & SALLAI 2006), as well as most other studies in freshwater habitats ( ERLINGE 1969, WISE et al. 1981, CARSS et al. 1990, KRUUK & MOORHOUSE 1990, SIDOROVICH
