Postmortem Examination of a Griffon Vulture Most Likely Killed by Lightning

Abstract

There are numerous reports of animals being struck by lightning, but the number of science-oriented studies in which a necropsy is performed, and the findings are documented, is relatively few and mostly focused on mammals. In contrast, analogous information about birds is scarce. The purpose of this article is to present the findings after a postmortem examination of an 85–90-day-old Eurasian Griffon Vulture (Gyps fulvus) that was most likely killed by lightning while in the nest in Sinite Kamani Nature Park in Bulgaria in 2021. The body was visibly burned, with keraunographic markings, lacked feathers and had fractured bones—typical findings in lightning strike injuries.

1. Introduction

Every minute, about 6000 lightning strikes happen all over the world [1]. This accumulates to over 8.6 million lightning strikes per year. Farm animals are more vulnerable to being affected by lightning because of their long span between the front and back legs, increasing the chance for a ground current (step potential) from a nearby strike [2].

Birds are unique because many of them can predict incoming storms by detecting the preceding decline of barometric pressure [3] and even alter their migration to avoid them [4,5,6].

Lightning injury or death occurs through six main mechanisms [7]: direct strikes, side flashes, step potential, touch potential, upward streamers, and proximity to the strike (blast). There are also secondary complications [7]), such as falling from higher altitudes due to momentary shock, being hit by detached by the lightning objects, burns due to materials in the surroundings catching fire, and psychological trauma.

Most often, lightning accidents are reported in popular media rather than in scientific literature, and many of the reports are compiled by authors with a non-scientific background, with the facts distorted to enhance the audience’s attention [7]. The scientific articles, when present, are mostly focused on mammals. In addition, as global warming is projected to increase lightning rates [8,9] and, consequently, lightning-related cases, it would be good to expand our knowledge about the different mechanisms and effects of lightning strikes on animals to improve their safety. Therefore, the purpose of this article is to present the pathoanatomical findings of birds struck by lightning and to improve our understanding of the role of rock-climbing pitons in lightning strikes so we could potentially reorganize their usage to enhance animals’ safety.

2. Materials and Methods

In Sinite Kamani Nature Park above the city of Sliven, Bulgaria, the Eurasian Griffon Vulture (Gyps fulvus) has been considered extinct as a nesting species since the 1980s. This was due to several factors, most notably the national use of poisoned baits [10] by livestock breeders and farmers, mainly against wolves, which led to the population collapse of all vulture species in Bulgaria. However, as a result of re-introduction and re-stocking efforts, and the subsequent release of 102 individuals since 2007, the Griffon Vulture has been successfully breeding again in the park after more than 40 years of absence [11]. The vultures are marked with standard metal ornithological rings, PVC colour rings and wing tags with matching inscriptions, and are monitored weekly by direct observations and camera traps [11].

In the park, monitoring was conducted regularly by a team from Green Balkans NGO. In May 2021, we discovered a hatched chick in a breeding pair’s nest. We waited for it to grow more in order to mark it. On 1 July 2021, an expedition was finally made. The nest was positioned in the middle of a cliff (Figure 1) and accessible only with climbing equipment. There were also metal rock pitons present from old climbing routes above the nest. In it was a chick, between 85 and 90 days old (Figure 2). The bird was marked by the aforementioned rings and wing tag, plus an additional OrniTrack-50 GPS/GSM transmitter by Ornitela Ltd., Vilnus, Lithuania, (all visible in Figure 3) attached by leg loop in accordance with the VCF (Vulture Conservation Foundation) recommendations. The transmitter takes GPS fixes every 10 to 60 min (depending on the battery charge), has a sleep interval at night to keep the battery, and uploads the data every 1 to 20 h (again, depending on the battery). This allows the bird’s movements to be tightly followed by our team. Upon detection, critical cases are duly reacted to on site. When we were leaving, there was an oncoming thunderstorm. Using “Blitzortung.org”, we extracted a 10 h timelapse (Figure 4) between 14:00 UTC (16:00 local time, UTC+2) on 01.07.21 and 00:00 (02:00 local time) on 02.07.21, which shows the movement and gradual fading of the storm. We left at around 18:00 UTC (20:00 local time). There were no other nearby storms or lightning strikes on record afterward.

On the next day (2 July 2021), the transmitter showed that the chick was outside the nest, which was unusual as it should not have been able to fly at that age. On 3 July 2021, a team went on site and discovered the bird dead on the ground below the nest (Figure 3). The body was taken for more detailed examination to the Wildlife Rehabilitation and Breeding Centre, part of Green Balkans—Stara Zagora NGO. Here, we report the findings after the postmortem examination of the chick, which was most probably killed by lightning.

We managed to find science articles about struck dead pigs [12,13], cattle [14], horses [15], deer [16], and whooping cranes [17]; the only bird-related article we found). The extracted findings from them are summarized in

Table 1. Pathoanatomic manifestations of the struck dead by lightning animals. (Note: This is a summary of all recorded animals in the group; some individuals may present all findings, some only one).

Animal Type	Pathoanatomic Manifestations of the Lightning Strike
Pig	Extensive hemorrhage in the pelvic region, fractures to the pelvis, last lumbar vertebra and ribs [12]; Fracture to the last lumbar vertebra and sacrum, displacement of the sacrum with transection of the spinal cord and spinal nerves, hemorrhages around the fractures [13]
Cow	Cerebrocortical necrosis [14]
Horse	Bilateral diffuse corneal edema [15]
Roe deer	Scorched streaks on the skin with hair loss, aspirated light-red foam in the trachea and bronchi, alveolar and epicardial hemorrhages, kidney and liver hyperemia [16]
Whooping crane	Coagulation necrosis in the kidneys, unspecified histological changes in the peripheral nerves, air sac membranes and heart [17]

.

3. Results

External examination (Figure 5 and Figure 6)—the body was visibly burned and covered with a lot of maggots. The skin was boiled-like, non-elastic, and pale. The plumage was almost completely missing, except on the wingtips. Some of the feathers were detached. There were faint keraunographic markings. The legs were burnt and had started to necrotize. The skull was fragmented and with missing parts—the rostral part of the lower beak (mandible) and part of the calvaria. The wing bones and the sternum were fractured as well.

Internal examination—the internal organs had liquefactive necrosis and were in advanced decay. There was no clear distinction between them. The muscle tissue was disintegrated (with rhabdomyolysis) and, along with the organs, had a mushy structure (soft and spreadable consistency), forming a relatively uniform liquid viscous mass.

In Table 1 below, are the extracted manifestations of the struck dead animals whose scientific articles we found. Our case showed partial similarities with the findings in the pigs (broken bones) and roe deer (scorched skin with hair loss).

4. Discussion

The presence or absence of lesions in victims of lightning accidents cannot be predicted because of the multitude of individual and environmental influencing factors. Consequently, identical injury patterns do not exist [18]. Common external manifestations of lightning injury are burns, keraunographic markings, and singed hairs or feathers [18]. Our necropsy findings were consistent with those. Due to the short exposure time, internal lesions are rare [18].

The nest was situated in the middle of a high cliff in a popular region among rock climbers. It had six metal pitons (from old climbing routes) positioned above it, approximately 2 m away from each other. There was also a direct record of a thunderstorm (Video 1). When thunderstorm clouds are present, the local electric field at the tips or corners of tall structures increases, which makes them more susceptible to lightning [19]. Moreover, tall structures attract the ground strike points toward them, and the deviation is positively correlated with the height of the structure [19]. Metal by itself does not attract electricity, but due to its high conductivity, it provides a path for the lightning to follow [20].

Having said that, we can assume that the most plausible cause of death was by a side flash of a lightning strike—the lightning most likely hit the top of the cliff and reached the chick through the pitons. A possible explanation for why it had fallen on the ground may be the blast—the strike generates a shock wave, which can reach a pressure greater than 100 bar, by massive expansion of air in the lightning channel [18]. The impact from both the blast and the fall may be the reason for the broken bones.

Alternatively, it could have struck the bird directly, burning it and breaking the bones.

5. Conclusions

Lightning strikes present an interesting area in which there is a lack of enough data about the mechanisms, factors, effects, and pathoanatomical changes in animals, particularly in birds. We hope that we have contributed valuable data about bird-related lightning deaths. Moreover, the case showed that rock-climbing pitons can be a big factor in lightning-related fatalities. There is a need for more research on this topic to better evaluate their role and eventually reorganize their usage—avoid putting them close to nesting places, or ones that can potentially be used as such, in order to lower the risk for lightning injuries.