The diet of otters was studied by the means of spraint analysis in the Bieszczady Mountains, in southeastern Poland. The study area extended over 25 km long stretch of the River San, about 1 km above Solina dam reservoir. Spraints were collected on seven 2 km long sections in 1993, and on three sections in 2010. In both study periods, otter spraints were collected in August, when the weather conditions were similar. The study revealed high contribution of mountain fish species such as Phoxinus phoxinus,Cottus spp., and Barbatula barbatula in otter diet. Diet composition along the River San showed little variation in 1993, except from the section closest to dam reservoir where it was characterised by the highest frequency of occurrence of perch Perca fluviatilis, cyprinids and amphibians. The share of perch in otter diet decreased, while that of noble crayfish Astacus astacus increased with the distance from Solina reservoir.
Changes in otter diet between 1993-2010 were characterized by an increase of the consumption of perch and cyprinids on the one hand,
and a decrease of the consumption of crayfish, on the other. Both spatial and temporal changes in otter diet reflected the effect of Solina
reservoir on the river community and the availability of prey to otters. The results indicate the ongoing changes in fish community influenced by the construction of Solina reservoir.
The diet of otters Lutra lutra was studied by spraint analysis in six river and stream habitats in eastern Poland. In all of them fish were the staple food of otters, constituting from 29 % to 96 % of prey consumed in particular seasons. In upland (river Tanew) and mountain (river San, streams Dwernik and Głęboki) habitats, bullheads (Cottus gobio) were the most frequently eaten fish throughout the year (with maximum contribution of 57 % in the winter diet on river Tanew). In these habitats otters preyed on total of 10 fish species, including: brown trout (Salmo trutta), stone loach (Barbatula barbatula ), brook minnow (Phoxinus phoxinus) and stickleback (Gasterosteus aculeatus). On the lowland rivers, otters relied on more fish species than on the upland and mountain rivers (14 species on river Czarna Hańcza and 12 species on the upper and lower course of river Biebrza). Beside various cyprinids, otters preyed on stickleback, perch (Perca fluviatilis), mud loach (Misgurnus fossilis), burbot (Lota lota) and pike (Esox lucius). On all rivers, except the lower Biebrza, most of fish (from 70% to 88%) captured by otters were less than 10 cm long. Amphibians and crayfish were two other important groups of prey. On small streams in the Bieszczady Mountains, frogs (mainly Rana temporaria) comprised up to 46% of otter prey. Crayfish (Ortonectes limosus) remains were recorded in otter spraints only on the lowland rivers: in summer crayfish comprised 52% of prey on the Czarna Hańcza River and 47% of prey on the upper Biebrza River. In upland and mountain habitats the food niche breadth of otters was lower (from B=2.62 to B=6.12) than on the lowland rivers (from B=3.10 to B=11.09) and did not differ much between the seasons. On the lowland rivers the food niche breadth was high in winter and low in summer, and the seasonal differences in otter diet were much more pronounced as compared to the upland and mountain habitats.
The study aimed to recognize whether the activity of a semi-aquatic invasive carnivore – the American mink Neovison vison – is related to the distribution of waterbird colonies. For this reason, we monitored mink occurrence in lake reedbeds and the fate of artificial nests imitating those of the great crested grebe Podiceps cristatus. The location of artificial nests in the grebe colony increased the probability of their survival compared to those placed outside the grebe colony. During the study, mink activity increased over time. In general, it was lower in colonies than outside of them, suggesting that the presence of natural nests does not increase the probability of mink occurrence in lake reedbeds. However, mink activity was negatively correlated with the distance from the lake shoreline and differed spatially according to the presence or absence of natural grebe nests. In grebe colonies, the probability of mink occurrence at greater distances from the lake shoreline was higher than outside, which can be explained by optimizing swimming effort while searching for prey. In conclusion, mink activity in colonies was lower than in areas with no waterbird nests, and nest location in a colony decreased predation risk by mink.
In summer 1992 through spring 1994, amphibian abundance and breeding was studied in the pristine temperate forests, typical of central European lowlands. The years 1991, 1992, and 1993 were among the driest in the recent decades, with the spring-summer precipitation 35% lower than the long-term average. In the primeval forests of Białowieża National Park, common frogs Rana temporaria spawned in small (on average, 0.2 ha) ponds (postglacial melt-out hollows) devoid of wood cover and characterised by water pH 5.1-6.0 (as measured in April). Breeding success of frogs, monitored qualitatively in 1993, was rather poor due to pond desiccation. The capture of amphibians on forest grids revealed that densities and seasonal dynamics differed between wet and drier deciduous forests. No amphibians were captured in the mixed coniferous forests during the study. In the wet ash-alder forests, on average, 39 amphibians ha-1 were recorded in late April, 12 ind ha-1 in summer, and 195–222 ind hasup-1 in autumn (September). In those forests, 90% of captured amphibians were common frogs, 6% common toads Bufo bufo, and 4% moor frogs R. arvalis. In the drier oak-lime-hornbeam forests, amphibians appeared in May, and increased in numbers towards summer (19–24 ind ha-1) and autumn (45–71 ind ha-1). Of all amphibians caught in those forests, 43% were common frogs, 38% common toads, and 19% were moor frogs. A majority of amphibians captured in autumn were young of the year. By mid-October, all amphibians had left the forest for their hibernation sites. Comparison of our data collected in very dry years with other available data from Bia∏owie ̋a Primeval Forest (various years between 1955 and 1998) revealed that summer indices of amphibian abundance were strongly positively correlated with rainfall in April-June of the census year and the previous year.
Invasive American mink and native polecats were live-trapped over a period of six years and radio-tracked during one winter-spring season in the lakeside habitats in NE Poland. The number of mink declined whereas number of polecats was stable during 1995–2000, however, except during one winter, mink were always more abundant in the study area than polecats. Significant differences in habitat utilization between radio-collared mink and polecats were observed. Mink moved only along the lake shoreline and showed no seasonal shift in habitat selection. In winter, polecats were most frequently located close to the lake banks, but they also stayed in barns and stables. In spring, they moved further from the lakes. There was considerable interspecies overlap of mink and polecat home ranges in February, and common use of the banks of the 500 m long unfrozen canal was recorded for 4 mink and 5 polecats. The pattern of daily activity of polecat and mink differed: mink were most active at dawn and in early morning whereas polecats at dusk and in beginning of the night. Individuals of both species coexisted in this small area at relatively high densities and to some degree exploited the same habitats, particularly in the vicinity of sites with access to open water.
We studied the amphibian breeding migration into an old established (the beginning of the 1990s) pond and a new one (2007), using drift fences in 2008-2011. The two ponds were located at a distance of about 0.5 km from one another in a post-agricultural landscape in the Mazurian Lakeland, north-eastern Poland. We examined the community structure and migration rates of adults and juveniles. The amphibian breeding communities were similar in the two ponds in each year. The moor frog Rana arvalis was the most
common species and comprised between 35 and 55 % of all adult amphibians migrating to both ponds. The new pond was colonized by adult amphibians in the first spring after its creation. In the second year, the amphibian migration rates doubled in the new pond and remained stable over the next two years. However, during the entire period of the study the old pond was a more attractive spawning site than the new pond, when measured by the number of migrating individuals of all recorded species. Despite some annual variation, there were no significant differences between the ponds in terms of the sex structure, mean body mass or migration timing of the predominant amphibian species. The most probable explanation for the observed differences in the rates of migration is breeding site fidelity.