Use of road underpasses by mammals and a monitor lizard in eastern Australia and consideration of the prey-trap hypothesis

Road networks continue to expand globally with predictable effects on ecological systems. Research into the effectiveness of road underpasses and overpasses for wildlife has been concentrated in North America and Europe. In Australia, most studies of underpasses have been of relatively short duration and without reference sites to give context to the measured rates of use. We studied 5–7 road underpasses at two locations in eastern Australia over 2–3 years, comparing camera trap detections of animals in underpasses with those at nearby forest sites. Three species of large macropod (wallabies and kangaroos) were frequently detected in the underpasses, with some underpasses traversed 1–4 times per week, and in many cases exceeded detections in the forest. The lace monitor (Varanus various) was detected in all underpasses, often once per week during spring and summer, and infrequently in the forest. At each location a different small macropod species, including one regionally threatened, showed a higher probability of detection in one underpass compared to several of the forest sites. The vulnerable koala (Phascolartos cinereus) was detected infrequently in underpasses and in the adjoining forest. The short-beaked echidna (Tachyglossus aculeatus) had a high probability of detection in a single underpass. The ‘prey-trap hypothesis’ postulates that predators will exhibit increased activity at underpasses as a consequence of prey being funnelled. We found the red fox (Vulpes vulpes) had high activity in some underpasses. However, its activity coincided less than expected with the activity of the mammals most at risk to it. Our results provide no consistent support for the ‘prey-trap hypothesis’. Instead, our study confirms the generic value of underpasses for a range of medium-large mammals as well as one large reptile. Habitat adjoining underpasses exerts a strong influence on their use and requires greater consideration to maximise underpass use.全球道路网络持续扩张，其对生态系统造成的影响亦在预料之中。此前针对野生动物道路下穿通道与上跨天桥使用效果的研究，多集中于北美与欧洲地区。在澳大利亚，多数针对下穿通道的研究周期相对较短，且未设置对照样地以明确其使用频次的参照背景。本研究于澳大利亚东部两处点位开展，耗时2至3年，对5至7处道路下穿通道进行监测，并将通道内的红外触发相机（camera trap）所捕获的动物检测结果，与周边林地样地的检测结果进行对比。研究在通道内频繁检测到3种大型袋鼠科动物（macropod，包括沙袋鼠与袋鼠），部分通道每周会被该类群穿越1至4次，多数情况下其通道检测频次高于周边林地。花边巨蜥（lace monitor，Varanus various）在所有下穿通道中均有被检测到，春夏季期间每周常出现1次，而在林地中的检测频次则较低。两处点位各有一种小型袋鼠科动物（macropod），其中1种为区域受威胁物种，其在某一处下穿通道内的检测概率高于多处林地样地。易危的考拉（Phascolartos cinereus）在道路下穿通道与毗邻林地中的检测频次均较低。短吻针鼹（short-beaked echidna，Tachyglossus aculeatus）仅在某一处下穿通道内具有较高的检测概率。「猎物陷阱假说（prey-trap hypothesis）」提出，由于猎物会被道路路网聚集至通道处，捕食者在通道内的活动频次也会随之升高。本研究发现，赤狐（red fox，Vulpes vulpes）在部分下穿通道内活动频次较高。然而，其活动频次与受其威胁最严重的哺乳类动物的活动频次的吻合度低于预期。本研究结果并未为「猎物陷阱假说（prey-trap hypothesis）」提供一致性的支撑证据。与之相反，本研究证实了道路下穿通道对于多种中大型哺乳类动物以及1种大型爬行类动物的通用保护价值。毗邻下穿通道的生境对通道的使用情况具有显著影响，若要最大化提升通道的使用效率，需对其周边生境给予更多考量。