1 INTRODUCTION

Globally, the development of power lines is expanding significantly. Usually, two types of power lines are constructed, that is, transmission lines, the high-tension wires that carry electricity with a magnitude larger than 60 kV from the power plant to substations, and distribution lines, the high-tension wires that carry electricity with a magnitude between 1 and 60 kV (APLIC, 2012). Due to their distribution above the ground, birds are susceptible to collisions and electrocutions during flight and perching. Around 12–64 million birds perish annually in the United States due to conflict with power lines (Loss et al., 2014). Similarly, 2.5–25.6 million birds die annually in Canada due to direct collisions with power lines (Rioux et al., 2013). Power line collisions occur when birds fly into wires, whereas electrocution at poles occurs when a bird completes a circuit by touching two or more energized parts or an energized part and the grounded part (Real et al., 2001). Electrocution predominantly happens on distribution lines, but collisions can occur on both distribution and transmission lines (Dwyer et al., 2016; Lehman et al., 2007). The collision of power lines and electrocution represent a highly consequential anthropogenic hazard that is frequently overlooked, yet significantly contributes to bird mortality (Cornwall & Hochbaum, 1971; Guil & Pérez-garcía, 2022; McNeil et al., 1985; Scott et al., 1972).

The issues of bird collision and electrocution are multifaceted, encompassing biological, topographical, meteorological, and technical aspects of power lines (APLIC, 2012). The susceptibility of certain bird species to hazards related to power lines may also be influenced by the characteristics of their surrounding habitats (Escobar-Ibáñez et al., 2022). The agricultural landscapes that serve as important foraging and roosting areas for numerous bird species also pose heightened risks of collision and electrocution (Collins et al., 2010; Sundar & Choudhury, 2005). Conversely, it is difficult to locate casualties in forests, and collision and electrocution incidents are also relatively uncommon in forests, possibly due to the increased availability of natural perches (Benson, 1981; Switzer, 1977). Power lines traversing through human settlements carry an elevated risk of electrocution to bird populations, while power lines that traverse wetlands, marshes, rivers, lakes, and ponds are more likely to result in collisions (Gális et al., 2019). Lack of natural perching spots, such as tall trees, in the vicinity of power lines can force birds to rest on power poles or wires, ultimately increasing the likelihood of electrocution (Khadka, 2022). The incidence of power line collisions varies among the habitats, for example, 113 collisions/km/year in grasslands, 58 collisions/km/year in agricultural lands, and 489 collisions/km/year near river crossings were estimated in the Netherlands in the 1980s (Erickson et al., 2005). The fluctuation in the population and spatial distribution of bird species during breeding, migratory, or wintering periods has a significant impact on the incidence rates of electrocution and collision (APLIC, 2006).

Large- and medium-sized diurnal birds, such as eagles, hawks, vultures, kites, and falcons, are the most common electrocution victims (Ferrer, 2012; Fransson et al., 2019; Gadzhiev, 2013; Guil et al., 2011; Haas, 2005; Prinsen et al., 2011; Škorpíková et al., 2020). Due to their broad wingspan, diurnal raptors (e.g., Black Kite Milvus migrans) and waterbirds (e.g., Cattle Egret Bubulcus ibis, Sarus Crane Grus antigone) are susceptible to electrocution (APLIC, 2006; Janss & Ferrer, 2001; Sundar & Choudhury, 2005). Agricultural and suburban areas have a higher incidence of corvids electrocution due to their increased population size, a larger body size propensity to use power poles for perching (APLIC, 2006). Whereas, passerines are less susceptible to electrocution due to their relatively smaller size but they are vulnerable to power line collisions due to their low aspect ratio (i.e., short wings and short tail) and swift maneuverability (Janss, 2000). Endangered species such as Gyps vultures are especially prone to fatal power line hazards due to their frequent use of power line towers as roost sites and vantage points (Mundy et al., 1992) with an estimated 4% decline in the local population of the Cape vultures (G. coprotheres) per year in the Eastern Cape Province of Southern Africa (Boshoff et al., 2011). Between 2010 and 2021, 15 bird species including vultures (144 individuals) have been electrocuted in Nepal as a result of the construction of electricity distribution lines without a proper assessment of their long-term impact on the environment (Bhusal, 2022; Chaudhary et al., 2019; Rasaili, 2022). Rare and endangered species with delayed mortality and low reproductive rates may experience population decline even if fewer adults are killed by power lines (Janss, 2000; Mundy et al., 1992). Therefore, in order to prevent bird fatality, it is imperative that thorough research be conducted to identify and understand the multiple factors that influence collisions and electrocutions.

Underground cabling of the low and medium voltage power lines is quite common in most developed countries, including Belgium, Germany, the Netherlands, Norway, and the USA, which is a boon to the bird's population with no risks of collision and electrocution (Haas, 2005). Although the subterranean cabling is theoretically viable, the price of installing it can be 4–10 times greater than the building of regular overhead lines. As consequences, above-ground power lines are abundantly constructed in most of the developing countries including Nepal. However, the specific data on the impacts of distribution lines on bird species in Nepal are rarely understood. Therefore, we aimed to provide the baseline data on bird collision and electrocution from distribution lines and understand the factors affecting power line collisions and electrocutions in putalibazar municipality. Our findings will add to formulating policies and programs in order to ensure the safety and conservation of avifauna in Nepal.

2 MATERIALS AND METHODS

2.1 Study area

We conducted this study in Putalibazar Municipality, the district headquarter of Syangja district of Gandaki Province (Figure 1). It has an area of 147.21 km² and extends from 28°03′18″N to 28°08′44″N and 83°47′30″E to 83°54′34″E, with a total human population of 41,743 individuals (CBS, 2023). The municipality is divided into 14 smaller administrative units called wards. The elevation of the municipality is 836 m from the sea level. This urban municipality came into existence in 1997 and was restructured on March 12, 2017 (GoN, 2017).

The distribution of birds in the study site is not uniform and varies on habitat type, geographic factors, and human effects. The primary vegetation types of the study area include Sal (Shorea robusta), Pine (Pinus roxburgii), Khair (Senegalia catechu), Dhale Katus (Castanopsis indica), and mixed forest (Bhandari et al., 2018). The primary crops grown in this region include paddy, maize, wheat, millet, pulses, and potatoes. Fruit trees include citrus, banana, guava, jackfruit, and peach (CBS, 2012). Although there is no detailed exploration of the wildlife in the municipality, the Kalij Pheasant (Lophura leucomelanos), Red Jungle Fowl (Gallus gallus), Cattle Egret (Bubulcus ibis), House Crow (Corvus splendens), Common Myna (Acridotheres tristis), etc. are regularly encountered birds.

3 RESULTS

We recorded 19 species of 853 individuals of birds representing 14 families and nine orders along the distribution line during the study period (Table A1 in Appendix 1). The mean (±SD) nest count in the trees located within the observation plot was 0.06 ± 0.329 [range: 0–2]. The mean (±SD) distance from the observation plot to the nearest agricultural land was 35.09 ± 48.38 m [range: 0–258 m], forest was 46.18 ± 54.72 m [range: 0–292 m], settlement was 51.66 ± 60.75 m [range: 0–292 m], and water source was 175.4 ± 172.21 m [range: 4–712 m].

3.2 Factors affecting the power line collisions and electrocutions

The probability of power line collisions and electrocutions was greatly impacted by bird abundance and the proximity to agricultural lands and human settlements (Table 2). The probability of an incident was higher in places with higher bird abundance and near agricultural lands and settlements (Table 2; Figure 2a–c).

TABLE 2. Generalized linear model describing the effects of given predictors on power line-related bird mortality in Putalibazar Municipality from November 2021 to May 2022.

Parameters	Estimate	SE	Z	p
Intercept	−0.471	0.670	−0.703	.482
Voltage: low	−0.367	0.662	−0.554	.580
Forest canopy cover	0.003	0.011	0.297	.766
Bird abundance	0.128	0.053	2.412	.016
Distance to water source	0.000	0.002	−0.259	.796
Distance to agricultural land	−0.030	0.013	−2.278	.023
Distance to forest	−0.002	0.005	−0.298	.765
Distance to settlement	−0.030	0.011	−2.823	.005

• Note: Model parameters include voltage (low or high), forest canopy cover (%), bird abundance, distance to water (m), distance to agricultural lands (m), distance to forest (m), and distance to settlement (m). Significant effects are in bold.

4 DISCUSSION

Our research indicates that collisions with power lines and electrocution have an adverse influence on some bird species in the Putalibazar Municipality. Although greater numbers were found of globally least concern species, mortality occurrences were also reported for globally threatened species, indicating that birds of Nepal are extremely sensitive to collisions with power lines and electrocution.

We discovered higher numbers of victims of Common Myna and House Swift in our study area, probably due to the large population of these species, as also reported in Spain (Janss, 2000). House crows and Rock Pigeons were the most electrocuted bird species, presumably due to their greater abundance and longer wingspan to complete the circuit between any two energized components (Janss, 2000). High voltage, namely 33 kV, was found to have a higher bird fatality than low voltage. However, our sampling was more extensive in the 33 kV line, covering a distance of 24.3 km and resulting in 34 bird deaths, whereas the 11 kV line, spanning 6.3 km, recorded nine bird deaths. Although large birds such as raptors, storks, and owls are more prone to short-circuit when resting if they come into touch with many conducting wires (Battaglini & Bätjer, 2015), our study shows that small-sized birds such as flycatchers or swifts are also affected by power lines.

The most important factor determining bird collision and electrocution is the abundance of the birds (Bevanger, 1994). The higher the bird population, the higher the possibility of mortality, which might be attributed to the high density and behavioral characteristics of species (Lehman et al., 2007). Therefore, while constructing the route for the distribution lines, it is necessary to monitor the bird abundance and composition prior to avoid undesired collision and electrocution. As agricultural lands and human settlements provide important habitats for various bird species (Grimmett et al., 2016; Katuwal et al., 2022), we observed an increase in collision and electrocution fatalities in the vicinity of agricultural land and human settlements. This might be due to the fact that birds utilize the power lines and poles within these ecosystems as perching sites while they forage for prey (Perez-Garcia et al., 2011). In addition to that, large number of power lines is built on agricultural land due to suitable conditions for the installation of utility structures (Dixon et al., 2017; Siriwardena et al., 1998; Wretenberg et al., 2006). Power lines in close proximity to bird concentration habitats, such as wetlands and agricultural land, are the most hazardous because birds establish breeding and wintering colonies and concentrate at higher densities, which dramatically increases the likelihood of collision (Andriushchenko & Popenko, 2012; Faanes, 1987; Malcolm, 1982). For example, around 1% of Sarus Crane (Grus antigone) population dies annually due electricity wires-related incidents in India (Sundar & Choudhury, 2005). Collision and electrocution-related mortality are also documented in the forest. However, it is difficult to discover the carcass, particularly in the forest and also in river basins, due to the abundance of scavengers and the fact that they are more difficult to detect than on agricultural land or in human settlements. Therefore, careful route planning is one of the most effective ways to reduce bird collisions with overhead power lines (D'Amico et al., 2018). We recommend attachment of markers onto the power lines in the form of plates, spirals, flappers, swivels, or spheres to increase their visibility are by far the most common mitigation measure applied to reduce bird collisions with power lines (APLIC, 2012; Barrientos et al., 2011; Prinsen et al., 2012). While the use of avian safe pole designed with sufficient separation between energized phase conductors (also called “phases”) and between phases and grounded hardware to accommodate at least the wrist-to-wrist or head-to-foot distance of a bird, insulation of exposed part or wire and installation of perch management techniques will help to reduce the electrocution incidents (Prinsen et al., 2012).

Our study has some limitations because it was conducted in a short period of time, which could have an effect on the rate of power line collision and electrocution incidents. We conducted bird surveys within a 10 m radius and not at all times of the year, which reduced the richness and abundance of bird species. We only visited the region four times between November and May, thus we may have missed some incidents, as the carcasses may have been taken or consumed by predators. Despite the fact that we consulted with the locals, we believe that it is insufficient. Hence, the number of power line collision and electrocution incidences may be greater in our study area than we reported. As a result, we advise continuous monitoring or monitoring at least once a week in order to identify all possible incidents.

5 CONCLUSION

We conclude that power line collisions and electrocutions are imposing substantial threats to the common and the threatened birds in Putalibazar Municipality. The chance of bird mortality owing to power lines was found to be significantly related to bird abundance and the distance to agricultural lands, and human habitation. We advocate for careful route planning and timely supervision of distribution lines, as well as the deployment of appropriate measures in order to decrease the likely risks of collision and electrocution to birds.

AUTHOR CONTRIBUTIONS

Suman Hamal: Conceptualization (equal); data curation (equal); formal analysis (equal); investigation (equal); methodology (equal); writing – original draft (equal); writing – review and editing (equal). Hari Prasad Sharma: Conceptualization (equal); data curation (equal); formal analysis (equal); methodology (equal); project administration (equal); supervision (equal); writing – original draft (equal); writing – review and editing (equal). Ramji Gautam: Conceptualization (equal); writing – review and editing (equal). Hem Bahadur Katuwal: Writing – review and editing (equal).

CONFLICT OF INTEREST STATEMENT

The authors declare no conflict of interest.