Effects of vehicle-passing frequency on forest roads on the activity patterns of carnivores

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In this study, we evaluated the effect and extent of linear human disturbance caused by vehicle traffic on forest roads on animal activity time. Our research focused on four sympatric carnivores (red fox, Vulpes vulpes; raccoon dog, Nyctereutes procyonoides; Japanese marten, Martes melampus; and Asiatic black bear, Ursus thibetanus) living in the forest region of northeastern Japan. From August to November 2019, we obtained data on the activity time for each species from nine infrared-triggered cameras installed along two types of unpaved forest roads with different vehicle frequencies (high or low) and subsequently assessed the effect of vehicle-passing frequencies on activity using kernel density estimation and chi-square test. Red foxes and raccoon dogs were nocturnal on all forest roads; however, their nighttime activities were significantly greater on the forest road with a high vehicle-passing frequency than on the road with a low vehicle-passing frequency. Japanese martens showed a nocturnal pattern on all forest roads, and there was no significant difference in the proportion of nighttime activities between the forest roads. Asiatic black bears were highly active during the daytime on forest roads with a low vehicle-passing frequency, but were highly nocturnal on forest roads with a high vehicle-passing frequency. Our results suggest that human disturbance influences the ratio of daytime to nighttime activity in carnivores; however, the extent and magnitude of this effect are limited. This finding indicates that the spatial scale of effects of human disturbance on the activity of each animal species should be assessed before habitat management programs are implemented.