Feeding habits of the otter and the American mink in Białowieża Primeval Forest (Poland) compared to other Eurasian populations

Abstract

Diets of the otter Lutra lutra and the American mink Mustela vison were studied by scat analysis on five woodland rivers and streams in eastern Poland. Fish constituted 51% of food biomass consumed by otters in spring‐summer and 40% in autumn‐winter, with common fish (perch Perca fluviatilis, pike Esox lucius, and roach Rutilus rutilus) being captured most frequently by the otters. Amphibians (mainly Rana temporaria, which also dominated in the living community) made up 34% of otters’ food biomass in spring‐summer and 58% in autumn‐winter. American mink relied on three prey groups: fish (40% in spring‐summer, and 10% in autumn‐winter), frogs (32% and 51%, respectively), and small mammals (21% and 36%). Out of available Micromammalia, mink strongly selected the root vole Microtus oeconomus. The cold season diet of both otter and mink depended on river size. On small rivers with forested valleys, otters and mink fed nearly exclusively on amphibians (72–90% of food biomass). With size of a river increasing and riverside habitat becoming more open (sedge and reed marshes instead of forests), otters shifted to catching predominantly fish (up to 76% in diet) and mink to preying on small mammals (up to 65% in diet). Review of literature on otter and mink in Eurasia showed that their diets did not change with latitude (as indicators of climate severity and duration of water freezing) but they depended on habitats. In otter diet, the mean share of fish declined from 94% (SE 1.7) on sea shores, to 71% (SE 2.9) on lakes and fish ponds, to 64% (SE 2.8) on rivers and streams. The roles of amphibians and crustaceans increased in the same gradient (from 0 to 15%, and from 3 to 7%, respectively). On inland waters, the abundance of crayfish was the essential factor differentiating otters’ diet composition. In Eurasia, the staple food types of American mink on rivers and streams were fish (on average, 27% in diet, SE 3.9), mammals (30%, SE 5.0), and amphibians (17%, SE 4.8), whereas on lakes and ponds mink fed predominantly on birds (on average, 33% in diet, SE 10.1) and fish (28%, SE 9.5). In the Palaearctic region, over a wide gradient of habitats, otters appeared strongly specialised on prey taken from water, whereas American mink was a typical generalist capable of utilising several prey groups originating from both water and land.

Diet of the Eurasian otter Lutra lutra on small watercourses in Western Poland

“…Obviously, to enable these ecological adaptations the otter is flexible in its feeding habits (Brzeziński et al 1993, Carss 1995, Lanszki and Körmendi 1996, Jędrzejewska et al 2001, Clavero et al 2003. Although there is no doubt that the otter is a piscivorous (Chanin 1981, Lanszki and Molnár 2003, Brzeziński et al 2006, it is characterized by flexibility in the type of prey caught (Lanszki et al 1999).…”

“…Moreover, river size, water discharge and riparian vegetation cover can influence the composition of the diet of otters. As an example, Jędrzejewska et al (2001) reported that the river type can affect the quantity of amphibians in its diet. Furthermore, the alteration of riparian habitats is often accompanied by the reduction of fish biomass, forcing otters to forage upon alternative prey (Weber 1990, Lanszki et al 1999, Clavero et al 2003.…”

“…Although otter diet has been widely investigated in a variety of habitats (for reviews, see: Jędrzejewska et al 2001, Clavero et al 2003, there is a lack of research focusing on feeding habits of otters living in small watercourses with high anthropogenic pressure in agricultural landscapes.…”

“…The occurrence of different types of prey was calculated in two further ways, such as frequency of occurrence (or FO) and relative frequency of occurrence (or RFO). Using appropriate coefficients of digestibility, which for individual groups of prey included fish -25, amphibians -18, birds -12, rodents -9, crayfish and molluscs -7, insects -5 (Jędrzejewska et al 2001, after Lockie 1961, we calculated the percentages of the biomass of food eaten.…”

“…All otter spraints, food remains and other traces of their presence were collected. Analysis followed the standard procedure (Goszczyński 1974, Jędrzejewska et al 2001): faeces were dried, washed on a sieve with a mesh diameter of 0.5 mm and dried again. Identification of the prey was made using a binocular microscope (10=2-4 magnification).…”