Influence of infrastructure, ecology, and underpass-dimensions on multi-year use of Standard Gauge Railway underpasses by mammals in Tsavo, Kenya.

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. 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. Results revealed hyenas and leopards used the underpasses more than expected whereas giraffes and antelopes used the underpasses less than expected. Generalized linear mixed-effects models revealed that underpass height influenced use by wildlife, with several species preferring to use taller underpasses. Electric fencing increased underpass use by funneling species towards underpasses, except for elephants and black-backed jackal for which it reduced underpass passage. We also found that the use of underpasses by livestock reduced the probability of use by nearly 50% for wildlife species. Carnivore species were more likely to cross underpasses used by their prey. 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. Our findings suggest a need for diverse and comprehensive approaches for mitigating the negative impacts of rail on African wildlife.