There is an urgent need to understand how modern railway infrastructure is differentially impacting the connectivity and conservation of various African species because many rail infrastructure projects are planned or underway in Africa 44. An understanding of how railway and road underpass design influences use by African savannah wildlife is lacking. This is further compounded by species and individuals differing in their propensity to use underpasses 42, 43. The optimal characteristics for wildlife underpasses along highways are known to be species-specific 28, 41, suggesting that it may be difficult to create universally optimal designs in areas with diverse wildlife species. In addition, ecological factors such as the presence of vegetation cover, forage, species involved, species interactions (e.g., predator–prey) and human activities are also important 26, 33, 38, 40. North American and European studies reveal that the effectiveness of underpasses is dependent on design factors such as size dimensions (i.e., height, length, and width) and location 27, 37, 38, 39. Moreover, there is a dearth of information on wildlife use of underpasses associated with roads or railways by wildlife in the African continent where these designs and technologies are increasingly being adopted (but see examples 34, 35, 36). Several research studies, mostly in North America and Europe, have examined the effectiveness of wildlife underpasses along highways 19, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, but limited studies exists for railways 18, 31, 32, 33. Wildlife corridors (e.g., underpasses, overpasses, culverts) along highways traversing conservation areas are a valuable mitigation tool for enhancing the permeability of transportation infrastructure for wildlife while preventing wildlife mortalities from vehicle collisions and encouraging connectivity 17, 18, 19, 20. However, with increasing railway traffic volumes and the expansion of high-speed trains, wildlife mortality from railways will likely increase 10, 16, and this will demand implementation and evaluation of mitigation measures to reduce wildlife mortality. Perhaps, this is because the impacts of railways are perceived to be negligible due to a lack of awareness and reporting, lower traffic flow than roads, and long traffic-free intervals among others 15. Although railways may have similar impacts as roads, little attention has been paid towards mitigation of the effects of railways on wildlife. Generally, railway traffic, like road traffic, may negatively impact biodiversity through increased wildlife mortality from road and rail kills, loss of population connectivity, habitat fragmentation, pollution (e.g., noise, chemical and light), and habitat loss 6, 10, 11, 12, 13, 14. Moreover, an increase in infrastructure is predicted to occur mostly in the tropics where there are high levels of biodiversity and susceptible ecosystems 8, 9. Linear infrastructure is essential for economic growth and development 1, but it is also widely regarded as a catalyst for biodiversity loss in natural ecosystems 2, 3, 4, 5, 6, 7. Our findings suggest a need for diverse and comprehensive approaches for mitigating the negative impacts of rail on African wildlife. Buffalo, livestock, and hyenas used underpasses characterized by vegetation with higher NDVI and near water sources while baboons, dik-diks and antelope avoided underpasses with high NDVI. Carnivore species were more likely to cross underpasses used by their prey. We also found that the use of underpasses by livestock reduced the probability of use by nearly 50% for wildlife species. Electric fencing increased underpass use by funneling species towards underpasses, except for elephants and black-backed jackal for which it reduced underpass passage. Generalized linear mixed-effects models revealed that underpass height influenced use by wildlife, with several species preferring to use taller underpasses. Results revealed hyenas and leopards used the underpasses more than expected whereas giraffes and antelopes used the underpasses less than expected. We assessed the influence of underpass dimensions, fencing, proximity to water and roads, Normalized Difference Vegetation Index (NDVI), presence of other species and livestock on underpass use by large and medium-sized mammals. Rail and road infrastructure is essential for economic growth and development but can cause a gradual loss in biodiversity and degradation of ecosystem function and services.
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