The mitigation of fragmentation due to high density road network has been a hot topic among environmentalists
and road construction engineers of South Korea. Over the last ten years 92 wildlife passages, 55 ecoducts and 37 wildlife underpasses, have been constructed on existing roads, and many more will be constructed in the future (Ministry of Environment of the Republic of Korea, 2006). We are at an early stage of data collection on wildlife vehicle collision and the role of traditionally non-wildlife-engineered passages, such as underpasses including bridges, culverts, and human underpasses, for wildlife passages.
The objective of this study was to analyze the effectiveness of the number, size, and density of non-wildlife-engineered passages. This study employed three monitoring methods: wildlife vehicle collisions, the passages use ratio (Servheen, 2003) and radio telemetry. The effectiveness of such unintended wildlife passage was evaluated by using the relationship between monthly wildlife vehicle collision data, number of usable passages, use rate of passages, and passage density.
The number of usable passages represents all crossing structures after excluding those inundated circular culverts during summer season, since they are impassable for most wildlife species. The use rates of wildlife passages were collected from 14 underpasses. They were seven circular culverts, two box culverts, and four human underpasses, and were selected from 31 structures constructed on a 6.6km segment of a four-lane highway. The landscape of study area mainly consists of rice fields on an alluvial plane and scattered forest, and the road runs along the stream. Every passage has similar surroundings. Wildlife monitoring was carried out for 12 months, from Sept. 2005 to Aug. 2006; using camera traps (an average of 239 camera operating days). The number of recorded mammals was 2,593, consisting of 13 species. We also documented 93 mammal vehicle collisions comprising 12 species by monitoring the same road daily over a period of two years (Sept. 2004-Aug. 2006).
The results of our analysis are as follows. First, the use rate of passages and the number of mammal vehicle collisions showed a positive correlation (r=0.890). Second, the fluctuation of the number of usable passages and collisions had no correlation (r=0.402). Third, the density of passages and collisions had a very weak positive correlation (r=0.559, pα=0.05). These results differed from following common expectations: higher numbers and use ratings of passages could cause less frequent collisions, high density areas of passage would cause fewer collisions, and the decreased number of passages would increase the use ratings of remaining passages. Fifth, most monitored mammal species with small-to-medium body sizes used all types of passage structures frequently, but water deer (Hydropotes inermis) rarely used these passage structures of under 0.7 on the openness index. Last, we found by radio telemetry that only one out of 13 radio-collared raccoon dogs was killed by vehicle `collision over a two-year period. However, a total of 12 raccoon dogs that had been killed by cars were found on the same road during the same period.
The results of our research can be summarized as follows. First, there were already enough usable passages for wildlife, in spite of seasonal blockage of some passages or the uneven spacing between passages. Second, there were many occurrences of wildlife vehicle collisions, but settlers showed relatively low collision ratio. Third, most collision victims might be wanderers or newcomers unfamiliar to existing passages or occupying settlers. Finally, water deer should be the target species for the construction of wildlife passages, and the size should be O.I of over 0.7. Vehicle collision of other mammal species can be reduced significantly by installing wildlife fences without worsening habitat fragmentation in the case of roads that have many non-wildlife-engineered passages.