Hyenas die also in road accidents
Which factors influence the risk of fatal collisions between vehicles and spotted hyenas in the Serengeti? Findings from a long-term study over three decades
The Serengeti National Park in Tanzania is home to large populations of wildlife species, including spotted hyenas (Crocuta crocuta). While many human activities are prohibited in the national park, driving is allowed in and through the protected area. Using a 34-year long-term data set, a scientific team from the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) analysed which factors significantly contributed to hyenas being run over and killed by vehicles. These were, firstly, the type of road, and secondly, the annual migration of the large ungulate herds in the Serengeti and the associated seasonal changes in the localisation of the prey animals of spotted hyenas. The findings provide new insights into which ecological and individual factors influence the risk of fatalities for carnivores in collisions with vehicles; they were published in the scientific journal Biological Conservation.
Worldwide, many wild animals are killed by vehicles even in protected areas. These negative impacts of roads continue to increase because of the growth of the human populations in the vicinity of protected areas and the growing interest in wildlife tourism. However, the factors that contribute to fatal collisions between wildlife and vehicles are still poorly understood.
The Serengeti National Park is covered by a network of roads. Main roads are gravel roads covered in murram which are used not only by tourist vehicles, supply trucks for tourist camps, park staff and scientists, but also by through traffic in terms of trucks and national bus lines throughout the year. In addition, there are a large number of unpaved tracks for wildlife observation and access to tourist camps. As part of a long-term study in the Serengeti National Park between 1989 and 2023, the Leibniz-IZW scientists found a total of 104 spotted hyenas that had been run over. They used these cases to investigate the spatial and temporal factors which contributed to spotted hyenas being run over and killed by vehicles, and explored to what extent spotted hyenas of a particular age group, sex or social status were affected.
Two factors turned out to be crucial. Firstly, hyenas were more often run over on main roads than on tracks, probably because vehicles travel faster there and there is more traffic. Secondly, the timing and location of fatal collisions coincided with the seasonal migration of the large herds of ungulates (blue wildebeest, plains zebra, Thomson’s gazelles), the main prey of spotted hyenas in the Serengeti. The results are consistent with other studies where the risk of being killed by a vehicle increases with the mobility and distance travelled by the animals. In addition, killed hyenas were found particularly close to watercourses and human dwellings, to which the hyenas are presumably attracted by the presence of human food waste.
"Contrary to expectations, the seasonal variation in the number of tourists in the region did not seem to play a role for the level of mortality," says Marwan Naciri, who joined the Leibniz-IZW for this project and is the lead author of the publication.
A special feature of the dataset was that some of the hyenas which were run over were individually known and therefore aspects of their life history could be explored in the analysis. This showed that adult females were most frequently run over, probably because they cover the longest distances, as they are the ones who regularly commute between the communal dens and the migratory herds in order to forage near the herds and nurse their cubs left at the communal dens in their home territory.
"Injuries from illegal wire snares also particularly affect adult female hyenas, as we found in a previous study," says Leibniz-IZW scientist Sarah Benhaiem, involved in both research projects. Road kills and death by snares are probably the main causes of mortality in adult hyenas in the Serengeti. Whether this mortality, which mainly affects adult females, threatens the viability of the spotted hyena population in the Serengeti is still unclear.
Road networks will expand in future. Knowledge of the factors which contribute to fatal collisions between wildlife and vehicles will help design effective mitigation measures. In the Serengeti, these are likely to include an improved surveillance of the current speed limit of 50 km/h, a stricter control of the prohibition of night drives and a limit to the number of vehicles on main roads. Good planning of road construction and implementation of mitigation measures will be essential to ensure the continued conservation of wildlife in protected areas.
Naciri M, Planillo A, Gicquel M, East ML, Hofer H, Metzger S, Benhaiem S (2023): Three decades of wildlife-vehicle collisions in a protected area: Main roads and long-distance commuting trips to migratory prey increase spotted hyena roadkills in the Serengeti. Biological Conservation 279, https://doi.org/10.1016/j.biocon.2023.109950.
Benhaiem S, Kaidatzi S, Hofer H, East ML (2023): Long-term reproductive costs of snare injuries in a keystone terrestrial by-catch species. Anim Conserv 26, 61-71. https://doi.org/10.1111/acv.12798.
Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW)
in the Forschungsverbund Berlin e.V.
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Dr. Sarah Benhaiem (German, English and French)
Scientist Dept. Ecological Dynamics
Tel.: +49 30 5168-466
Steven Seet (German, English)
Head Science Communication
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