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1.Bats roosting in tree cavities, under loose bark or just on branches in foliage, so-called tree-dwelling bats, are a very diverse and abundant group of species. Although they can be very different species with locally distinct needs, radical exploitation of forest habitats and global changes have meant that many of them are regionally endangered and survive today only in small populations. To help develop appropriate conservation policies and management plans, much research in recent decades has been focussed on inferring habitat selection by tree-dwelling bats. However, large variability in the reported selection patterns makes it difficult to suggest some more-or-less universal and easily applicable management recommendations, also for regions in which nature conservation awareness is low. 2. We created a meta-analytic model to explore selection patterns at a global scale. Phylogenetic relationships among species and additional variables were included to explain discrepancies between studies. 3.A meta-analytic model showed that bats are selecting trees with trunk diameters that are larger than those of randomly selected trees, and this pattern is consistent within each biogeographical region. However, meta-regression revealed that the detectability of the selection depends strongly on the structural variability within the study environment (size of randomly selected or surrounding trees in forest stands, forest fragmentation, habitat disturbance) and on the methodological approach that has been applied (the length of the study). We found stronger selection for larger trees in non-fragmented and less disturbed forests than in fragmented forests with high habitat disturbance, and, strikingly, short-term studies yielded results with stronger selection than long-term studies. 4. Our results suggest that patterns of roosting habitat selection by bats may be overestimated in some studies. In conclusion, we propose that further research should be conducted in all types of forest ecosystem (data from the tropics are currently missing). Future studies should include at least three years of data collection, in order to avoid estimation bias in habitat selection patterns.

Collisions and electrocutions on power lines are known to kill large numbers of birds annually on a global scale. We conducted comprehensive research focused on bird mortality caused by 22 kV and 110 kV distribution power lines in 13 Special Protection Areas in Slovakia. In the period between December 2014 and February 2016, 6,235 km of power lines were inspected twice during two periods (12/2014–03/2015 and 04/2015–02/2016) of field survey. In addition an intensive study was conducted during the second field survey at one-month intervals on power lines identified as the most dangerous for birds to collide with. As a result, 4,353 bird carcasses and bird remains representing 84 bird species and 14 orders were identified. Electrocution was suspected for 76.72% and collision for 23.28% of fatalities. Raptors were associated with 40% of all identified victims of electrocution. Two peaks of incidence were recorded, the first in March with a high rate of electrocutions as well as collisions of swans, pheasants, common blackbirds, ducks and herons, and the second in September predominantly featuring electrocution of raptors, magpies and corvids. We were unable to quantify seasonal patterns of mortality due to the limited sample of repeated mortality surveys resulting from the large grid of inspected power lines. We conducted comprehensive statistical analysis of more than 100 configurations of pylons and calculated their potential risk towards birds. Strong spatial correlation was revealed in the data set. Metal branch pylons and corner pylons with exposed jumper wires passing over the supporting insulators above the cross arms were the most dangerous configuration, accounting for 34.72% of total recorded electrocution fatalities (0.13 carcass/pylon). Cases of electrocution were also recorded for two bird species of major conservation concern in Slovakia: saker falcon (Falco cherrug) and eastern imperial eagle (Aquila heliaca). The results of this study may substantially improve conservation management and policies needed to reduce bird mortality.

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Logistic regression (LR) models are among the most frequently used statistical tools in ecology. With LR one can infer if a species’ habitat use is related to environmental factors and estimate the probability of species occurrence based on the values of these factors. However, studies often use inadequate sampling with regards to the arbitrarily chosen ratio between occupied and unoccupied (or available) locations, and this has a profound effect on the inference and predictive power of LR models. To demonstrate the effect of various sampling strategies/efforts on the quality of LR models, we used a unique census dataset containing all the used roosting cavities of the tree-dwelling bat Nyctalus leisleri and all cavities where the species was absent. We compared models constructed from randomly selected data subsets with varying ratios of occupied and unoccupied cavities (1:1, 1:5, 1:10) with a full dataset model (ratio 1:31). These comparisons revealed that the power of LR models was low when the sampling did not reflect the population ratio of occupied and unoccupied cavities. The use of weights improved the subsampled models. Thus, this study warns against inadequate data sampling and highly encourages a randomized sampling procedure to estimate the true ratio of occupied:unoccupied locations, which can then be used to optimize a manageable sampling effort and apply weights to improve the LR model. Such an approach may provide robust and reliable models suitable for both inference and prediction.

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