Volume 13 (2019): Issue 1 (December 2019)

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.

In 2015–2016, 6,429 km medium-voltage power lines with 76,430 pylons were checked for bird mortality in the Czech Republic. 1,326 bird victims of power lines were found, 156 of which died after collisions, and 1,170 birds were electrocuted. They belonged to 60 species from 12 orders, and birds of prey made up almost half of all victims. Steel pylons bearing several cross-arms including upper and crosswise jumpers were identified as most dangerous from the electrocution point of view. On the other hand, pylons in straight lines with Pařát cross-arms (triangular arrangement of conductors without any horizontal bar) were among the least dangerous, and when they had a simple perch fitted below the cross-arm, no mortality was recorded. But these pylons are new in practice and despite becoming widely used recently, they form less than one tenth of all pylons in the Czech Republic. On other pylons various types of mitigation measures have been installed. Commonly used plastic covers and plastic strips have proved to be especially effective, but only in cases when they are undamaged and correctly installed.

Flight observations and carcass searches were carried out along distribution power lines in Slovakia. 77 km of 22 kV and 110 kV lines were marked on a total of 108 sections to evaluate the effectiveness of three types of bird flight diverters (FireFly Bird Diverter, RIBE Bird Flight Diverter and SWAN-FLIGHT Diverter) designed to increase power line visibility. Numbers of carcasses were compared before and after installation of the devices and reaction distances on marked power lines were surveyed. We observed a 93.5% reduction (93 vs. 6) in the number of fatalities under the marked power lines after line marking (06/2016–06/2019) compared to the period before installation (12/2014–02/2016). 2,296 flight reactions were observed and an estimated total of 41,885 individuals (57 bird species belonging to 13 orders) were recorded with their reactions to marked lines in the period 06/2016–06/2019. After installation of bird diverters, there was a low proportion of flight distance observations at the closest distance, i.e. up to 5 m, indicating that birds reacted further away from marked lines. Although we lack flight observations for the period before the installation of diverters, the reactions of birds at greater distances and reduced number of bird victims under marked lines indicate that all tested diverters have a positive effect on reducing the number of avian collisions with power lines.

Power lines represent an important and increasing worldwide cause of avian mortality due to collisions involving flying birds. One positive and very important fact is that only some parts of potentially dangerous lines are responsible for the majority of killed birds. These sections need to be identified and treated with proper mitigation measures. In this article we present a specially-prepared methodology aimed at classifying power lines according to the risk they present. The identification of power lines with the highest risk of possible bird collision requires easily-accessed biological, technical and landscape information. In addition to analyses of these main inputs, our methodology also evaluates the influence of power line orientation relative to the important migration routes of birds, the effect of nearby tree growth higher than the evaluated power lines, and the complexity of landscape relief. Based on these three additional inputs, it is possible to produce a digitalized map showing with one-meter accuracy the location of power line sections with the high/middle/low mortality risk due to collision for any existing or newly-planned grid. Sections with highest risk should be considered as priority for the implementation of mitigation measures including e.g. installation of bird flight diverters. Our methodology was prepared for 22 kV and 110 kV distribution power lines in Slovakia. It is flexible enough to be applied equally to any geographic conditions and/or bird community, different voltage levels and construction designs of power lines. Our methodology can be applied by ornithologists, nature conservancy organization and power line system operators to implement environmental and cost-effective mitigation measures.

In the period between the years 1976 to 2016 we monitored the nesting site distribution of two populations of saker falcon (Falco cherrug) concentrated in the highlands and adjacent lowlands of western and eastern Slovakia. In western Slovakia we recorded nesting by 56 pairs and 514 nestings, and in eastern Slovakia we observed nesting by 32 pairs and 245 nestings. There were similar nesting success rates in both regions, with pairs producing on average 3.2 young in every successful nest. During the monitored period as a whole a total of 1,788 young saker falcons were raised. At the same time all the pairs gradually resettled in the lowlands, and in the new environment the nesting success rate significantly improved (81.1% compared with 57.1 % in the highlands). This change of nesting biotopes was caused by the impacts of intensive exploitation and environmentally inappropriate forest management, with the accompanying excessive disturbance of nesting birds, but at the same time the disappearance of ground squirrel (Spermophilus citellus) colonies led to a change in the food spectrum for the observed saker falcon pairs. We evaluated the falcons’ feeding habits in western Slovakia between the years 1977 and 2016 (49 pairs; 1–17 pairs/year) and in eastern Slovakia between 2009 and 2016 (12 pairs; 1–3 pairs/year). Altogether 17,669 prey items were identified. From 1976 onwards mammals (Mammalia, 19.8%, 24 species) became gradually less represented as a component in the falcons’ diet compared with birds (Aves, 79.9%, 58 species). In areas of western Slovakia we found stable and predominant proportions of domestic pigeons (Columba livia f. domestica) ranging from 52% to 62%. The proportion of pigeons was distinctly lower in eastern Slovakia (31.5%), compensated for by larger shares of common vole (Microtus arvalis), common starling (Sturnus vulgaris), Eurasian magpie (Pica pica) and hooded crow (Corvus cornix). The common starling (9.5%) was a significant prey species in the lowlands of western and eastern Slovakia alike. Mammals were mostly represented by common voles (9.8%), European hamsters (Cricetus cricetus, 5.3%), ground squirrels (2.1%) and hares (Lepus europaeus, 1.6%). Changes over time in the composition of falcons’ prey were also evaluated over five periods in western Slovakia.

Long-eared owls’ winter roosts located within forest, compared to their winter roosts in human settlements, often escape human attention. Only minimum information has been published about winter roosts located deep in the forest. During the years 2005 to 2016, we collected long-eared owl pellets at irregularly occupied forest winter roosts. Compared to the diet at winter roosts in human settlements, the long-eared owls roosting in the forest surprisingly significantly more frequently hunted the common vole. Moreover, we did not record higher consumption of forest mammal species in the diet of owls at forest winter roosts. Long-eared owls roosting in human settlements hunted significantly more birds. The results show that, despite the location of deep forest winter roosts, long-eared owls preferred hunting the common vole, i.e. hunting in open agricultural land. The study also points out the lack of knowledge about winter roosts located deep in the forest.

The demographic responses to severe weather by top-level predators, including birds of prey, are underreported and/or unknown. Severe storms are predicted by climate change models to increase globally and in frequency into the 22^nd century. In April 2018, a population of breeding Cooper’s hawks (Accipiter cooperii) in central Wisconsin, USA, experienced three days of heavy snowfall in the most severe storm, in pre-incubation-stage, for 39 years (1980–2018). Here I report select demographic outcomes of this nesting population following this intense weather. The median hatching date of 10 June in 2018 was the sixth latest such metric in those 39 years (and the latest in 22 years since 1996) for this population, which has advanced its breeding schedule about 1.3 days/decade due to climate change or warming. Survival of a total of 16 color-marked breeding adults, 15 males and 1 female, observed pre-storm in the nesting areas, was 100% up through the late nestling stage in the same nesting areas where these birds were initially detected in 2018. Average clutch size (4.4 eggs/nest) and average brood size (4.0 young/nest) were similar to the overall average annual metrics of these demographics for this population in the earlier 38 study years. Nest success, whereby 95% of 21 nests with eggs produced advanced-aged young, was higher in 2018 than the overall average of 77% nest success rate during the earlier years. The later timing of hatching in 2018, likely due to the severe spring snowstorm, appeared to have no deleterious effects either on survival of the breeding adults or on the reproductive output of this healthy study population. Tree-canopy prey may have served as important alternative food for this typically ground-foraging raptor in 2018.

There is scarce information on the migration patterns and population size of the Eurasian marsh harrier (Circus aeruginosus) in Iraq in general and in the southern Mesopotamian wetlands in particular. From February 2018–April 2019, a total of 11 field expeditions were conducted in the Central Marshes (219,700 ha), one of the major Mesopotamian wetlands and Iraq’s National Park, a RAMSAR and UNESCO site. Two of the field survey objectives were to determine the spatial and temporal distribution and estimate the population size of the migratory/wintering Eurasian marsh harrier in the Central Marshes. Distance sampling on three line-transects covering a study plot of 40,000 ha was conducted. Among other wintering Circus harriers, the Eurasian marsh harrier was the most abundant species with a total of 93 individuals recorded. The estimated species densities were 0.0042–0.035 individuals/ha, and the estimated size of the Eurasian marsh harrier migratory population in the Central Marshes was 922.7–7,689.5 individuals. Moreover, the migration phenology and breeding status of the Eurasian marsh harrier in the Central Marshes were investigated. Our efforts did not confirm the breeding of this species during recent years, or since the inundation of the Mesopotamian wetlands in 2003. Furthermore, hunting and trapping were identified as major threats affecting the species which need urgent conservation action.

In winter 2013/2014 a roost of long-eared owls in Bojnice Spa (central Slovakia) was formed by two subgroups situated 12 meters apart from each other. The diets of both subgroups and the direction of the owls’ departure from the roost were studied at monthly intervals. Owls of the Pinus-subgroup left the roost in a significantly different direction compared with the owls in the Picea-subgroup. The common vole was the most hunted prey in both subgroups. However, comparing the alternative prey of the two subgroups, the wood mouse and other mammals were found significantly more often in pellets of the Picea-sub-group, whereas birds were more frequent in pellets of the Pinus-subgroup. Our results suggest that the different prey hunted by the two subgroups may be a consequence of diverging hunting areas with different availability of alternative prey species.