Provide mammals with escape routes from canals
Overall effectiveness category Likely to be beneficial
Number of studies: 5
Background information and definitions
Mammals may be attracted to canals and other artificial waterways for drinking. When such waterways have steep sides, mammals may fall in and be unable to escape. Such waterways may also act as barriers to animal movements and mammals may attempt to cross them but be unable to exit the water whilst some aquatic mammals may also enter deliberately but struggle to exit the water. In such cases, mammals may be at risk of drowning (e.g. Peris & Morales 2004). Escape routes may be installed to enable mammals that have fallen in or otherwise entered the water to escape back onto land. These may take the form or ramps, ladders, shallow inlets or other structures that mammals could use to climb out.
Peris S. & Morales J. (2004) Use of passages across a canal by wild mammals and related mortality. European Journal of Wildlife Research, 50, 67–72.
Supporting evidence from individual studies
A study (year not stated) in a swimming pool and on a stretch of a canal in Lower Saxony, Germany (Schneider & Waffel 1978) found that a platform was used by at least five mammal species to exit water and both metal ramps and vegetated islands by at least two species Roe deer Capreolus capreolus, red deer Cervus elaphus, wild boar Sus scrofa, red foxes Vulpes vulpes and badgers Meles meles used timber platforms to exit from waterways. Rabbits Oryctolagus cunniculus and hedgehogs Erinaceus europaeus used a ramp covered with meshed metal to exit from waterways. Red foxes and badgers used vegetated islands to leave water. Timber platforms were tested by releasing medium-sized (e.g. foxes) and large mammals (e.g. deer) into a swimming pool, and guiding them to a platform. A ramp covered with meshed metal was tested for small mammals (e.g. rabbits) and a 'vegetated island' (4.5 m × 2.5 m; 1.5 m above water level) was tested for deer, badgers and foxes. The vegetated island comprised timber beams 'planted' with leafy branches either fixed to the bank or anchored in the middle of a steep-banked stretch of canal.Study and other actions tested
A before-and-after, site comparison study in 1978–1982 of a steep-sided canal in Germany (Wietfeld 1984) found that installing shallow-water inlets and ramps did not reduce mammal drownings. There was no evidence of large mammals leaving the canal by inlets or of a reduction in the number drowned after inlet establishment (after: 15 individuals drowned in one year; before: 11 drowned in two years). There was no evidence of small mammals using ramps as exits. There was no significant difference in the density of drowned small mammals on canal sections with and without ramps where the length of canal surveyed without ramps was twice the length surveyed with ramps: hamster Cricetus cricetus (with: 50; without: 80), common vole Microtus arvalis (with: 14; without: 25), water vole Arviola terrestris (with: four; without: seven). Inlets were shallow shelving exit points (250–500 m apart) established in spring 1979. Sand at eight inlet entrances was checked daily in September 1979, and April–May of 1980 and 1981 for mammal footprints. The canal was searched every 2–3 days for drowned animals before and after inlet establishment (1978–1980). Ramps (≤50 m apart) were installed in May 1982. Sand at ramp exits was checked daily over 20 days in August for small mammal footprints. Live-trapping was conducted over 13 days.Study and other actions tested
A study in 1982–1985 in a canal between farmland and desert in Arizona, USA (Rautenstrauch & Krausman 1989) found that ramps and ladders reduced mule deer Odocoileus emionus drownings. Of at least 282 times that deer fell into the canal over a 40-month period, three deer drowned, 116 escaped via steps, 79 via ramps and eight via metal ladders. A further 50 escaped without using structures and 10 were pulled out alive. Exit points of 16 deer were not determined. Over two previous years, before escape routes were improved, 18 deer drowned on the same canal section. A 15-km-long canal section, 5.5–10 m wide was studied. There were six dams, five with existing escape stairs. In 1980–1981, three escape ramps (3 m wide, at 25° to the direction of water flow with a 25% slope) were added. There was also one 1.3-m-wide iron ladder and seven reinforcement-bar ladders (date of installation not stated). Wire cables (3 cm diameter) across the water surface, directed trapped deer toward each escape structure. Deer were monitored and reported by canal workers and by monitoring tracks at 1–3 day intervals in June 1982 to September 1985 (total 478 visits). Drownings in 1979–1980 were logged by canal staff.Study and other actions tested
A study in 2002–2005 in two wetland areas in the Netherlands (Lammertsma et al. 2006) found that providing mammals with escape or access routes from and into canals resulted in their use by Eurasian otters Lutra lutra. In 2002–2005, twenty-four animals, comprising a mix of wild-caught and captive-bred individuals, were released at two sites. In one of the areas, modifications to canal banks were made to aid entry and exit by otters to and from the water. Use of exits from canals was monitored by direct observation, observation of tracks in the snow, and identification of otter faeces.Study and other actions tested
A replicated study in 2012–2015 of two irrigation canals in Jujuy, Argentina (Albanesi et al. 2016) found that at least three mammal species used escape ramps to exit from waterways. Two tapirs Tapirus terrestris, one collared peccary Pecari tajacu and one red brocket Mazama americana were recorded exiting water via ramps. Thirteen additional mammal species were detected on escape ramps though it is unclear if they used these to exit from water. Two irrigation canals were studied, one crossing a forest reserve and the other crossing sugar cane and citrus plantations. In 2012–2013, fifteen 3-m-wide escape routes with 20-cm-high steps were constructed. Escape routes were 0.15–1.8 km apart. Monitoring was conducted using camera traps set in October 2012, May 2013, March 2014 and December 2015. Camera traps were 2–3 m from escape routes and were set to take one photo every 5 minutes for approximately 40 days.Study and other actions tested