Aim  Land use intensity has been recognized as one of the major determinants of native species declines. The re‐expansion of species previously constrained by habitat degradation has been rarely investigated. Here, we use site occupancy models incorporating imperfect detection to identify the land use drivers of the re‐expansion of the Eurasian otter (Lutra lutra). Location  Czech Republic. Methods  We applied multi‐season occupancy models to otter presence–non‐detection data collected in three national surveys (1992, 2000, 2006) at 552 sites (11.2 × 12 km grid cells). Model parameters included site occupancy, colonization and extinction probabilities, and detection probability at a sub‐site level. We modelled changes in occupancy over time as a function of agricultural, urban and industrial land use and change in the extent of agricultural land use. Results  Under the best fitting model, occupancy was estimated to be 34.6% in 1992, 51.3% in 2000 and 83.7% in 2006. Detection probability was neither perfect nor constant. Occupancy probability in 1992 was negatively related to land use gradients. Colonization was more likely to occur where a reduction in agricultural land was larger. Variation in extinction and colonization rates along land use gradients resulted in increased occupancy in industrial and especially urban landscapes. Conversely, occupancy remained almost unchanged along agricultural gradients. Main conclusions  Dynamics of otter expansion were strongly associated with the two main patterns of the rapid environmental transition that has taken place in the Czech Republic since the early 1990s. Results show that a reduction in intensive agricultural land use led to an increase in otter distribution, providing evidence of the impact of agricultural land use on stream ecosystems. Moreover, otters recolonized urban and industrial landscapes, probably as a result of extensive reduction in water pollution from point sources. Our results suggest that active conservation of otter populations should focus on restoration of freshwater habitat at large scales, especially in agricultural landscapes.

Abstract In the last decades, large carnivores – the grey wolf (Canis lupus), Eurasian lynx (Lynx lynx) and brown bear (Ursus arctos), and to a certain extent also the wildcat (Felis silvestris) – have increased their distribution ranges throughout Europe. Monitoring of their current distribution and population trends in the Czech Republic is crucial for the effective conservation and elimination of possible conflicts with humans in the future. In the last years, many projects focused on small-scale monitoring of large carnivores were implemented in the Czech Republic and the neighbouring mountain ranges of Slovakia. Using their results, we compiled the dataset from different regions and analysed the recent distribution of large carnivores and the wildcat. The distribution maps are based on verified data on the presence and reproduction in 2012–2016. This is consistent with the standardized methodology used across Europe. The Eurasian lynx was the most widespread of all large carnivore species in the Czech Republic, with the two trans-boundary populations (Carpathian and Bohemian-Bavarian-Austrian) occupying 94 out of 868 squares (10.8%) of the mapping grid of the Czech Republic. Reproduction was confirmed in 46.8% of the occupied squares. The grey wolf occupied 6.8% of the squares in the Czech Republic and its reproduction was confirmed in 10.2% of the occupied squares. Three reproducing packs belonging to the Central European lowland population were confirmed and the area occupied by the species increased three times within the study period. The brown bear occupied 2.8% of the squares of the Czech Republic – the area is restricted to the Carpathians – with no signs of reproduction; its distribution fluctuated heavily during the study period. The wildcat occupied the smallest range of the Czech Republic among the studied species (1.4% of the squares) but its reproduction was confirmed in a trans-boundary area (White Carpathians) at the Slovakian side of the border. The wildcat also significantly increased its range from one to six squares during the study period.

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Using a tame animal, the impact of otter (Lutra lutra) disturbance on over-wintering carp (Cyprinus carpio) was monitored in two experiments, 133 and 140 days, respectively, over two consecutive winters (November-April). The level of stress in over-wintering carp exposed to various intensities of disturbance by otters was quantified using biological indicators of stress (cortisol, cortisone, indices of nitrogen, carbohydrate, lipid and mineral metabolism and activity of basic blood plasma enzymes) taken from blood plasma of stocked carp at the end of the winter seasons (when the photoperiod was 12 light:12 dark, respectively, 13L:10D). Moreover, condition (Fulton's coefficient of condition and fat content in muscles) and mortality rate of that carp were measured after over-wintering and also after the subsequent vegetation period. The analysis of blood and tissue samples of experimental fish showed changes in nitrogen, carbohydrate and mineral metabolism as well as levels of hormones and fat reserves. Higher response to stress in metabolism of carp with lower intensity of disturbance by otter suggests that high level of disturbance can lead to metabolic adaptation of carp to stress. The effect of stress on the mortality rate of carp during the over-wintering is not clear. Nevertheless, the negative effect of stress on survival, condition and growth rate of carp in the subsequent vegetation period was not observed.

Summary 1.Visitation rate is a measure of the frequency with which animals visit specific locations of interest. This information is crucial for various problems in the conservation and management of animal species, e.g. to determine the risk wildlife poses to human managed resources or the predation risks of nests. An important assessment tool, especially for cryptic animals, is to count indirect signs of presence, such as tracks or faeces. 2.Here we propose a maximum likelihood-based method that uses information on the age of tracks or signs, and we show that existing visitation rate/probability estimators are special cases of this more general approach. 3. Using simulated data, we compared the performance of the new visitation rate estimator to three other estimators, including the most commonly used estimator. These estimators make use of either fresh, aged or total signs, whereas our approach uses information simultaneously on both fresh and aged signs. The new estimator is, on average, in excess of three times more accurate than the next best estimator. Moreover, the new approach is very flexible and can be applied for sampling regimens with irregular time intervals between sampling. 4. We demonstrate the application of the method to field data by estimating the visitation rate of Eurasian otters ( Lutra lutra ) to a commercial fish pond. To facilitate the use of this method, we provide an easy-to-use Excel workbook and give recommendations on the most efficient sampling regimens. 5. Synthesis and applications . Visitation rate is an important quantity that can be estimated by repetitive sampling of indirect signs. We demonstrate the advantage of incorporating information explicitly on the age of signs over existing approaches. The new estimator can be applied to any species for which it is possible to discriminate between aged and new signs or tracks, and should be widely applicable in ecology and conservation biology.