Seasonal variation in the feeding habits of riparian mustelids in river valleys of NE Belarus

In 1986-1997, diet composition of the native riparian mustelids: the otter Lutra lutra (Linnaeus, 1758), the European mink Mustela lutreola (Linnaeus, 1761), the polecat M. putorius (Linnaeus, 1758), and the naturalized one, the American mink M, vison (Schreber, 1777) was studied in relation to seasonal changes of the habitats (the Lovat river, NE Belarus). Amphibians, fish, crayfish, small mammals, and birds appeared the essential prey resources supporting the guild of riparian mustelids. In the river valleys, the two mink species and polecat were characterized by opportunistic feeding habits, whereas the otters specialised on fish. In spring and autumn, Dogs were important prey to all mustelids studied. The trophic niches of the two mink species were wider than those of the otter and the polecat. In the seasonally changing environmental conditions, the American mink appeared more opportunistic predator than the European mink. Food niches of the three native mustelids overlapped notably less with each other (Pianka's alpha from 0.24 to 0.70) than with the American mink (n from 0.60 to 0.89). The obtained data suggest that in river valley habitats the naturalized American mink may be a strong competitor for prey with the native riparian mustelids, especially the European mink and the polecat.