Human-induced mortality an overlooked threat for raptors in Nepal

Summary

Raptors play a unique role in ecosystem services and are regarded as effective indicators of ecosystem health. In recent years, varieties of anthropogenic factors have threatened the majority of raptor species worldwide. Nepal is considered a global hotspot for threatened and declining raptor species, but there is limited information on the direct human threats to the raptor populations living in the country. In this paper, we identify important anthropogenic threats to raptors in Nepal based on raptor mortality data collected by powerline surveys and from monitoring of GPS-tagged raptors, complete various reports, and social media. We found that powerlines, poisoning, and persecution, mainly shooting, are significant threats to raptors in Nepal that were largely overlooked previously. We report 54 electrocuted raptors affecting eight species, 310 poisoned raptors of 11 species, and five persecuted raptors of four species; among them vultures are the most affected (>88%). Based on our findings, to safeguard the future of Nepal’s raptors, we propose the retrofitting of power poles and the use of flight diverters on powerlines in the most affected areas to reduce raptor interactions with powerlines, as well as an effective conservation education programme to prevent the use of unintentional poisoning.

Introduction

Raptors are apex aerial predators and effective indicators of ecosystem health (Donázar et al. 2016). Species like vultures are important for the rapid disposal of animal carcasses (Markandya et al. 2008, Ogada et al. 2012a, b) and other raptors may limit damage to agriculture by rodents (Paz et al. 2013) or birds (Kross et al. 2012, Inagaki et al. 2020). In some countries, e.g. Nepal, Iran, or India, vultures provide important cultural services through “sky burials”, which is the consumption of human carcasses by aerial scavengers. Despite their ecological, cultural, economic, and aesthetic value, raptors are among the fastest declining groups of birds globally, with 18% of raptor species on the verge of extinction and an additional 52% declining in most of their range (McClure et al. 2018). Loss of habitat caused by the spread of agriculture and deforestation and the increase of non-natural mortality caused by human persecution, poisoning, and interactions with human infrastructure are the main threats to raptors (McClure et al. 2018).

Nepal is considered a global hotspot for threatened and declining raptor species, as well as for generally understudied vultures (Buechley et al. 2019, Santangeli et al. 2019). Nepal is home to approximately 19% of 321 species of diurnal raptors (e.g. vultures, eagles, hawks, falcons, etc.) in the world (BirdLife International 2018a). Among the total number of diurnal raptors inhabiting Nepal, 20% (n = 12) are designated as globally threatened with extinction – four species are “Critically Endangered” (CR), four are “Endangered” (EN), and four are “Vulnerable” (VU) – and an additional 13% (n = 8) are “Near-threatened” (NT) (BirdLife International 2018b). Raptors constitute 28% of the globally threatened birds found in Nepal (BirdLife International 2018b). In the national Red List of Nepal, 47% (n = 28) of raptor species are threatened with extinction (13 CR, four EN, and 11 VU) and additionally 7% (n = 4) are NT (Inskipp et al. 2016). Seven out of 10 Important Bird and Biodiversity Areas (IBAs) in the world with the highest number of globally threatened raptor species exist in Nepal. The numbers of these threatened raptors are declining in six out of these seven Nepal IBAs (McClure et al. 2018).

A report on the state of Nepal’s birds by Inskipp et al. (2011) indicated that pesticide poisoning (from various routes including agriculture, poison used to control livestock predators) alone threatens 41% of raptors in Nepal. Since the 1990s, the vulture population has dramatically declined as a result of non-steroidal anti-inflammatory drugs (NSAIDs), primarily diclofenac, that have caused the near extinction of resident Gyps species in south Asia (Oaks et al. 2004, Shultz et al. 2004). After a massive conservation effort in recent years by several conservation agencies, the rate of decline has been reduced and the vulture population is recovering (Galligan et al. 2020). However, unintentional poisoning not only occurs when birds are exposed to toxic NSAID residues in livestock carcasses (Oaks et al. 2004), but also when they feed on intentionally poisoned carcasses deposited by livestock keepers targeting mammalian carnivores, e.g. feral dogs (Virani et al. 2011, Ogada et al. 2016, Santangeli et al. 2016), or when poachers attempt to eliminate the presence of vultures as signs of illegal activities (Ogada et al. 2016). Nevertheless, knowledge of unintentional poisonings in Nepal is limited to vulture mortality due to the veterinary use of NSAIDs. Although unintentional poisoning due to NSAIDs is the most critical threat to vultures in South Asia (Botha et al. 2017), raptors also face other anthropogenic threats, such as interaction with human infrastructure and human persecution.

In a changing world, the interactions with human infrastructures have become one of the most important causes of non-natural bird fatalities in recent times (Botha et al. 2017, McClure et al. 2018). Electrocution and collision with powerlines (Figure 1) have been recognised as significant human-induced sources of non-natural mortality for birds worldwide, and especially for raptors (Bevanger 1998, Lehman et al. 2007, Prinsen et al. 2011), including significant numbers of endangered raptors such as Saker Falcon Falco cherrug (Harness et al. 2008, Dixon et al. 2020) or Steppe Eagle Aquila nipalensis (Karyakin and Novikova 2006, Levin and Kurkin 2013). Raptors are especially sensitive to electrocution as they often use pylons as hunting perches or roosting sites (APLIC 2006, Lammers and Collopy 2007, Janss 2000), occurring mainly in distribution powerlines (less than 36 kV) because the distance between wires or between wires and non-insulated materials is small and allows a bird to make contact simultaneously between them (APLIC 2006). In contrast to electrocution, collisions may happen in the whole powerline network (Bernardino et al. 2018). It is very common for birds not to be killed instantly in collisions but that injury caused by collision may lead to death at some distance away from the lines. So, most of the mortality cases caused by collision are hard to record (Loss et al. 2015). Avian fatalities caused by electrocution and collision have been mainly studied in North America and Europe (over 80% studies) but are scarce in other ranges (Guil and Pérez-García 2022). In Asia, the existing studies are mainly from Mongolia (Harness et al. 2008, Dixon et al. 2013 a, b, 2017, 2018, 2020) and knowledge of powerline mortality of raptors in Nepal is virtually absent.

Figure 1. (A) Electrocuted Himalayan Vulture Gyps himalayensis (Photo: Bhojraj Thapa). (B) Burnt feathers of White-rumped Vulture Gyps bengalensis due to electrocution (Photo: Tulsi Subedi).

Finally, human persecution is recognised as a significant threat to birds worldwide (Madden et al. 2019). Birds of prey are persecuted because they are perceived as predators of domestic birds or other game animals, or in some places, such as in Africa, they are killed so that their body parts can be used in belief-based practices (Buij et al. 2016). Studies on bird hunting in Asia are scarce and most are focused on China (Liang et al. 2013, Kamp et al. 2015, Chang et al. 2019).

In view of the recognised global importance of Nepal for raptors and the striking scarcity of knowledge on the most important human threats, the aim of this study was to compile, from fieldwork and review of various documented records (reports and social media), the human-related causes of unnatural bird mortality such as interaction with powerlines, persecution, and poisoning. The paper will discuss the potential impact of these sources of mortality on long-lived raptor populations in Nepal, the establishment of systematic monitoring strategies, and possible mitigation measures.

Methods

Three different methods were used. On the one hand, we systematically sampled powerlines to determine mortality on these infrastructures. Secondly, five different species of raptors were tracked with GPS transmitters. This allowed us to evaluate impartially the causes of mortality, especially those that are more difficult to detect through systematic monitoring, such as poison or persecution. Finally, a review and compilation of information on anthropogenic mortality cases from a varied set of information sources was carried out. This opportunistic information, although not systematic, provides an overview of the situation (e.g. Rebolo-Ifrán et al. 2023).

Powerline survey

Between 2018 and 2021, we conducted a survey of electricity distribution poles in five regions of Nepal: Chitwan, Lumbini, Annapurna, Kathmandu, and Pokhara, to record the raptors and other bird casualties. The survey was conducted for 12 days in 2018, nine days in December 2019 and January 2020, and five days in February 2021. Each powerline was sampled for electrocutions on the poles. Unfortunately given the orographic and vegetation/habitat conditions, adequate monitoring could not be carried out to assess the impact of the collisions. We walked entirely in each sampled line segment of 24.2 km, inspected each pole-top, and searched the ground within a radius of 5–7 m around the base of each pole for the presence of avian carcass and feather remains (Harness and Wilson 2001, Dwyer and Mannan 2007). Most of the carcasses found showed obvious signs of electrocution (i.e. burnt feathers, legs, or feet), thus carcasses found below poles or electric lines were considered cases of electrocution. Our survey was mainly conducted in the winter period.

GPS-tracking raptors

A total of 21 individuals belonging to five species, Bearded Vulture Gypaetus barbatus (n = 11), Himalayan Vulture Gyps himalayensis (n = 3), Red-headed Vulture Sarcogyps calvus (n = 1), Mountain Hawk Eagle Nisaetus nipalensis (n = 3), and Indian Spotted Eagle Clanga hastata (n =3), were tracked with GPS transmitters between 2016 and 2020, and a total of 8,798 bird days were monitored (see details in Supplementary material Table S1). Each bird was monitored daily from a remote computer. If the repeated GPS locations were obtained from the same place, the site was visited for ground truthing and causes were recorded (e.g. mortality or failure of GPS unit; see details in Subedi et al. 2020).

Published data compilation and opportunistic information collection

To assess the knowledge on unnatural mortality of raptors in Nepal, we conducted a revision of scientific articles, newspaper reports, and social-media posts to compile records (Rebolo-Ifrán et al. 2023). The raptor mortality recorded on opportunistic observation was also included. We obtained the following data from each record: date; location; species involved; number of individuals affected; mortality causes.

Results

Electrocution and collision in powerlines

In a total of 440 power poles (24.4 km) surveyed in the systematic sampling, we recorded the mortality of 43 birds of 11 different species. Birds of prey accounted for 14% of the total mortality, giving an electrocution rate of 1.4 birds of prey/100 poles or 0.48 raptors/km. A total of five different species were found, the most affected being the Himalayan Buzzard Buteo refectus, with two fatalities. Among the non-raptors, we recorded a mortality rate of 8.7 birds/100 poles or 1.53 birds/km, with the crow group being the most affected with 33 individuals of three different species (Table 1).

Table 1. Bird fatalities recorded from systematic and opportunistic powerline monitoring in Nepal between 2018 and 2021.

* Data from GPS-tagged bird.

Of the 21 GPS-tagged raptors, the most likely cause of death of three individuals (one Bearded Vulture and two Mountain Hawk Eagles) was the collision and electrocution with a powerline. This represents 9% of the known causes of mortality for GPS-tagged Bearded Vultures and 67% for Mountain Hawk Eagles (Table S1).

In addition to the systematic transects and GPS-tagging data, we managed to collect opportunistic data from outside the transects by our team or provided by local people. A total of 15 individuals of three species: Himalayan Vulture, White-rumped Vulture Gyps bengalensis, and Barn Owl Tyto alba, were recorded from outside the systematic sampled area. In addition, the local people informed us that a total of 30–40 vultures were electrocuted in 2020 and 2022, at a 32 kV Midim Hydropower project’s transmission line at Bhorletar in Tanahu district, where the powerlines pass close to the community-managed cow rescue site; this is a regular food source for vultures. No publications or news reports of electrocution or collisions were found up to the completion of this work.

Unintentional poisoning

Of the 21 GPS-tagged raptors, we lost two Indian Spotted Eagles, out of three GPS-tracked individuals, due to poisoning by pesticide used for agriculture. In addition, we reported one Bearded Vulture (a recently fledged juvenile from a GPS-tracked adult pair) that had died due to poison bait used to exterminate carnivore mammals.

In the case of unintentional poisoning, we collected four accounts from field observations, eight from news reports and social media, one scientific paper, and one from GPS tracking (Table 2). Between February 2010 and June 2019, a total of 205 vultures of eight species (all Nepal’s vultures except the Long-billed) were reported dead, largely due to use of poison baits. On 21 April 2021, a total of 69 vultures (35 White-rumped, 31 Himalayan, one Slender-billed Gyps tenuirostris, and two Cinereous Aegypius monachus) were found dead due to consuming poisoned dog carcasses at western Nawalparasi. Similarly, use of poison baits killed a total of 26 Himalayan Vultures (14 in Dhorpatan Hunting Reserve, nine in Bhagalpur Koshi, and two in Bihauri Dang); one White-rumped Vulture at Koshi, and more recently in March 2023, five White-rumped Vultures in Nawalparasi (Table 2). In addition, we received a report of a Common Kestrel Falco tinnunculus and Steppe Eagle, with bent necks and firmly closed claws suggesting a poisoning case.

Table 2. Raptor fatalities due to use of poison baits.

* Eight species of vultures found in Nepal except Indian Vulture.

Human persecution

Within a year, we reported five cases of shooting: one Bearded Vulture, one Himalayan Vulture, two Mountain Hawk Eagles, and one Himalayan Buzzard. Among 21 GPS-tagged raptors, a Mountain Hawk Eagle was shot by the local people at Dhampus village. Another four cases were collected from social-media posts one of which showed a Himalayan Vulture captured and harassed to death; the remaining three cases were related to shooting.

Discussion

Human activities are the major challenges for raptor conservation in Nepal and impact almost all raptors (O’Bryan et al. 2022). Our study primarily focused on the impacts of powerlines, poisoning, and persecution. In Nepal threats to raptors other than the impact of NSAIDs on vultures are highly overlooked. Until recently no systematic studies have been conducted on threats (other than NSAIDs) to raptors, resulting in a lack of information in which to develop conservation strategies. This article helps to provide information on how the growing numbers of powerlines, unintentional poisoning, and human persecution are threatening raptors in Nepal.

Powerline impact

There is no doubt that these figures under-represent the true magnitude of the impact of powerlines on birds in Nepal, because we have not adjusted these values for rates of dead birds lost to scavengers such as dogs, cats, jackals, or hyenas; a study in Europe has shown 32% carcass removal rate in the first two days (Ponce et al. 2010). It is also likely that a number of electrocuted birds suffer burns and subsequently die from wing and leg necrosis away from the powerlines.

The 11–32 kV rural distribution electric poles vary in design and potential to electrocute birds. The conducting wires can be plastic coated and thus insulated and present, when properly constructed, a negligible electrocution risk. However, if overly clamped or tied off, naked areas of wire may make some poles a threat. Naked wires pose a threat on the cross-arms and poles that support them as well as in the mid-section when an oncoming bird may hit one wire and cause a flashover. The design and material of the poles and the cross-arm are critical in determining the risk of electrocution from powerlines (Guil et al. 2011). The poles and cross-arms of older pylons installed in Nepal were usually made of wood (a poor conductor except in wet conditions) and cross-arm design was horizontal with all phases above it. In the last decade, new powerlines have been built with concrete or metal poles and all the cross-arms are made of metal, frequently with short pin-insulators (a device that isolates a wire from a physical cross-arm). These new materials and designs are better conductors of electricity, and the new insulators reduce the distance between the bird and the live components (i.e. the wires and cross-arm), resulting in a considerable increase in the risk of bird electrocution (Guil et al. 2011). Additionally, new pylon designs vary even between adjacent pylons, which can complicate the determination of the “potential electrocution risk” of entire powerlines. However, at the pylon scale, it is possible to identify individual poles that pose a very high risk when they occur in an area of high use by sensitive species and their technical configuration is hazardous (Pérez-García et al. 2017). During our fieldwork, we learned which of the flawed designs are most commonly used in Nepal (Figure 2).

Figure 2. Common arrangement in electric power poles in Nepal. (A) Double dead-end pole with flat arrangement; (B) simple triangular arrangement; (C) double dead-end switch pole; (D) double dead-end pole with transformer.

Unintentional poisoning

Poison baits have been identified as a major emerging threat to vultures and other scavenging raptors in Europe and Africa (Margalida 2012, Ogada 2014) and, in particular, unintentional poisoning using poison baits, including dog poisoning (Santangeli et al. 2022). Our data seem to point to this being the case in Nepal, where most unintentional poisonings have occurred from attempted poisoning of dogs. It is known that livestock keepers in the mountainous ranges of Nepal are willing to poison carnivores to minimise attacks on their livestock (Mehta and Heinen 2001, Theile 2003). Very high percentages of local people are aware or perceive that poison is used in the retaliatory killing of mammalian carnivores in the Annapurna Himalaya ranges of Nepal (Subedi et al. 2018). This is likely to have a high impact on raptors, as many raptor species including vultures, eagles, hawks, or kites, are known to scavenge.

Our data however have also shown cases of intoxication from the use of agricultural products. Farmers are known to use excessive amounts of organophosphate in paddy fields, targeting a wide range of insect pests that has an adverse impact on amphibians (Nataraj and Krishnamurthy 2020), a preferred diet of Indian Spotted Eagle during the breeding season (Gurung et al. 2019). Therefore, pesticide poisoning is likely to have a high impact on raptors. Consumption of organophosphate-contaminated amphibians is potentially the most likely cause of mortality in Indian Spotted Eagles in Nepal’s rice-farmed areas. In the 1960s, Peregrine Falcons Falco peregrinus were extirpated from the eastern USA due to the effects of dichlorodiphenyltrichloroethane (DDT), an organochloride pesticide (Peakall and Kiff 1988).

Lead poisoning poses a significant problem for raptors. The most remarkable case was the California Condor Gymnogyps californianus which resulted in a near-extinction of the population (Snyder and Snyder 2000, Carpenter et al. 2003). In Asia, a high concentration of lead has been observed in Cinereous Vultures (Nam and Lee 2009), but the assessment of lead poisoning in other raptors and countries remains limited. Hence, it is crucial to evaluate the impact of lead poisoning on Asian vultures. To accomplish this, it is necessary to collect and analyse tissue or blood samples. Unfortunately, Nepal lacks the capacity for such assessments and the government has not prioritised these activities.

Recently, there have been growing concerns about additional NSAIDs (i.e. aceclofenac, ketoprofen, nimesulide, flunixin, carprofen, and phenylbutazone) as they are lethal to vultures (Galligan et al. 2022, Naidoo et al. 2018). Government policies are required for the strict banning of such drugs for veterinary purposes.

Human persecution

Monitoring and documenting cases of human persecution presents a formidable challenge. In our study, the sole means of obtaining records was through the use of GPS-tagged raptors that proved to be the only reliable source of information at our disposal. In several places of Nepal, e.g. the Himalayan range and adjacent areas, raptors are perceived to be predators of domestic fowl and other game animals (Pohja-Mykrä et al. 2012, Madden et al. 2019). Ranging data provided by GPS-tracked Bearded Vulture (11 birds) suggested that about 70% of their home range remains outside protected areas in Nepal and in human-dominated areas (Subedi et al. 2020), and 48% of the home range area of Mountain Hawk Eagle (three birds) remains within agriculture areas. Ranging data indicated these raptors are highly associated with human-dominated landscapes, and this is likely to increase the risk of human persecution, such as the killing of a few individuals as a revenge for predating domestic fowl (e.g. Mountain Hawk Eagle – a NT species), or the use of body parts in belief-based practices, especially Bearded Vulture (Acharya et al. 2010, Subedi et al. 2018). Although this is not a worrying situation at present, people believe the presence of vultures on their property signals a bad omen and other raptors predate poultry/livestock, thus they deliberately damage the nest sites, and damaging nests of CR species might cause irreparable loss. Public awareness is an important tool, and motivating the public sufficiently could safeguard the population of declining raptors in rural landscapes.

Silent synergic impacts on population dynamics

The synergistic effect of the losses of raptors due to human-related mortality (i.e. electrocution, poison baits, and persecution) may be counteracting conservation efforts, for example in the case of vultures with the ban on non-steroids. Some of these mortalities are very low and localised but when added to the others they may place a significant burden on the population dynamics, especially if we take into account the fact that many of these species have low annual productivity. Human-induced mortality (other than the effects of NSAIDs) of CR vultures (e.g. White-rumped Vulture) could pose a significant conservation challenge. After many years of extensive work on captive breeding of White-rumped Vulture, they have now been released in the wild. If such challenges persist, the survival of released vultures is questionable. The declines of vultures may cause the risk of increasing the population of facultative scavengers (e.g. feral dogs, rats, etc.), which act as reservoirs for several diseases thus increasing the rates of infectious disease transmission (Markandya et al. 2008, Ogada et al. 2012a). Also, the culture of certain communities such as the Parsi communities in India and Tibetan Buddhist could be affected. Species like Mountain Hawk Eagle and Indian Spotted Eagle are already in very small numbers within their range in Nepal. If the non-natural mortality continues due to anthropogenic activities, it is highly likely a significant proportion of populations of such rare species will be severely impacted.

The effect on the dynamics of the species can have a wide spatial impact. In Nepal, an east to west southern corridor of raptor migration exists in the foothills of the Himalayas (Juhant and Bildstein 2017). Approximately 15,000 migratory raptors, mostly the EN Steppe Eagle and NT Himalayan Vulture are counted every autumn from a single watch site (Subedi 2015, Subedi et al. 2017). Therefore, it is likely that a much higher number of raptors could migrate through the Himalayan foothills to reach their wintering ground. The southern lowland belt of Nepal where the farmlands and grasslands dominate is the major Nepal wintering area for many species of migratory raptor. Southern Nepal is also home to some of the remaining populations of at least three CR Gyps species that were decimated due to diclofenac use. Wintering sites, including short stopover sites, are mainly in these human-dominated landscapes where thousands of lethally designed power distribution poles exist, and poisoning and human persecution still occurs. Nationally this distribution network is growing rapidly and acting as the killing fields for resident and migratory species that breed in northern latitudes of Asia, such as in Russia, Mongolia, China, etc., an emerging and important threat to raptors and other birds of the country.

In addition, new threats to raptors may emerge in Nepal over the next decades. In particular, the expansion of renewable energies worldwide, as a consequence of the energy crisis and the need to reduce emissions, could have a significant impact on raptors (Serrano et al. 2020). If we want to avoid a vulture or raptor crisis in Asia, we must take measures to manage the expansion of these human infrastructures. This is particularly relevant for very mobile species for which it is not enough to avoid the deployment of renewables within protected areas (Pérez-García et al. 2022).

What are the solutions?

This is a pilot study to document important sources of unnatural mortality of raptors, although three sources (i.e. electrocution, unintentional poisoning, and persecution) seem to be the major threats. More systematic mortality data collection is required with longer duration and covering major landscapes of the country. Tracking the raptors using GPS transmitters can provide a good source of such information. If the birds can be retrieved it is important to perform necropsies to ascertain the cause of mortality.

While efforts are being made to enhance our understanding of their impact, it is imperative to simultaneously commence work on mitigating these threats. To address raptor electrocution, it is crucial to conduct thorough Environmental Impact Assessment studies, utilise bird-safe designs, insulate power wires, and implement measures like suspended wires under cross-arms (APLIC 2006). Construction with exposed electric wires should be avoided. State regulations are necessary to designate excluded areas, establish safe design standards, and enforce penalties for non-compliant companies (Guil and Pérez-García 2022) This implementation is urgently needed before the network continues to grow and its future correction will be too costly in economic terms. Finally, unintentional poisoning using poison baits and human persecution seems to be an important cause of raptors’ mortality, and is probably underestimated due to the difficulty of monitoring. Educating communities about the impact of such poison baits to non-target species is vitally important, as a single poison bait can kill hundreds of vultures at a time, highlighting the urgent need for comprehensive awareness programmes.