Background information and definitions
Pipelines can extend hundreds of kms and may represent substantial barriers to mammal movements if they lie at or just above the surface of the ground. Crossing points can be either elevated sections of pipe with space for mammals to pass beneath, buried sections or sections with crossing ramps constructed over the pipe.
Supporting evidence from individual studies
A study in 1981–1983 of three sites along a pipeline across tundra in Alaska, USA (Curatolo & Murphy 1986) found that buried pipeline sections were used more frequently than their availability as crossing points by caribou Rangifer tarandus. Buried pipeline sections accounted for 10 of 180 crossings (6%) at one site, 5 of 41 crossings (12%) at a second site and 65 of 732 crossings (9%) at a third site. These proportions were all higher than the proportion of pipeline that was buried at these sites (2%). Ramps (20–50 m wide) were installed across buried pipeline sections at three study sites. Sites covered 180–275 ha, each including 1.7–2.2 km of pipeline. Sections not buried were elevated 1.2–4.3 m above the ground. A crossing comprised one or more caribou crossing the pipeline, with >50% of group members successfully crossing. Crossings were documented by direct observations in late June to early August of 1981–1983.Study and other actions tested
A study in 1977–1978 of a pipeline across tundra in Alaska, USA (Eide et al. 1986) found that pipeline sections elevated specifically to permit crossings of animals underneath were not used by moose Alces alces or caribou Rangifer tarandus more than were other elevated sections. Of 81 crossing sections elevated to facilitate mammal crossings, 13 (16%) were used by moose, a similar rate to the 754 of 6,526 other elevated sections (12%) that were crossed. Caribou used four of 53 specifically elevated crossing sections (8%) available to them, a lower rate than the 10% of remaining elevated sections used as crossing points. Along a 145-km-long pipeline, 81 pipe sections were elevated specifically to permit large mammal passage underneath. These sections were ≥3 m high. Remaining sections, were of variable, but generally lower, height. All elevated pipe sections were 18.3 m long between supports. Animal passage was determined by footprint surveys after fresh snow. The pipe, separated into three sections, was surveyed on 11–15 occasions in October 1977–February 1978 and 1–5 occasions in March–April 1978.Study and other actions tested
A controlled study in 2006–2007 in boreal mixed-woodland in Alberta, Canada (Dunne & Quinn 2009) found that mammals used wildlife crossings over oil pipelines. Camera-trapping showed that successful crossings were made by deer (white-tailed deer Odocoileus virginianus and mule deer Odocoileus hemionus) on 746 of 904 approaches (83%), by moose Alces alces on 157 of 178 approaches (88%) and by coyotes Canis latrans on 52 of 59 of approaches (88%). Crossings were also made by lynx Lynx canadensis and black bear Ursus americanus (twice each) and gray wolf Canis lupus (once). Snow-tracking showed that deer had a higher successful pipeline crossing rate at wildlife crossings (96% of approaches) than along pipeline sections without crossings (90%). Moose success rate at crossings (66%) was lower than on sections without crossings (77%). In March 2006, five crossing structures of soil and vegetation (≥20 m long, ≥4 m wide, 2–3 m high) were installed along 5.5 km of pipeline. Use of these crossings, and of gaps under elevated sections along 1.6 km of pipeline, was monitored. Snow track surveys were carried out at three-week intervals in February–March 2006 and November 2006–April 2007. Camera traps were installed along each pipeline section with two at each crossing for one year (2006–2007).Study and other actions tested