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Providing evidence to improve practice

Action: Install wildlife warning reflectors along roads Terrestrial Mammal Conservation

Key messages

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  • Fifteen studies evaluated the effects on mammals of installing wildlife warning reflectors along roads. Nine studies were in the USA, three were in Austalia, two were in Germany and one was in Denmark.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (10 STUDIES)

  • Abundance (1 study): A before-and-after study in Australia found that when warning reflectors were installed (along with speed restrictions, reflective wildlife signs, rumble strips, wildlife escape ramps and an educational pamphlet) a small population of eastern quoll re-established in the area.
  • Survival (10 studies): Five of eight controlled or before-and-after studies in the USA and Germany found that wildlife warning reflectors did not reduce collisions between vehicles and deer. Two studies found that vehicle-deer collisions were reduced by reflectors and one found that collisions were reduced in rural areas but increased in suburban areas. A before-and-after study in Australia found that when warning reflectors were installed (along with speed restrictions, reflective wildlife signs, rumble strips, wildlife escape ramps and an educational pamphlet) vehicle collisions with Tasmanian devils, but not eastern quolls, decreased. A review of two studies in Australia found mixed responses of mammal road deaths to wildlife warning reflectors.

BEHAVIOUR (5 STUDIES)

  • Behaviour change (5 studies): Three of four studies (including three controlled studies), in the USA, Denmark and Germany, found that wildlife warning reflectors did not cause deer to behave in ways that made collisions with vehicles less likely (such as by avoiding crossing roads). The other study found that deer initially responded to wildlife reflectors with alarm and flight but then became habituated. A replicated, controlled study in Australia found that one of four reflector model/colour combinations increased fleeing behaviour of bush wallabies when lights approached. The other combinations had no effect and none of the combinations affected red kangaroos.

Supporting evidence from individual studies

1 

A replicated, controlled study in 1981–1984 in a forest-grassland area in Washington, USA (Schafer & Penland 1985) found that wildlife reflectors reduced road deaths of deer Odocoileus sp. Fewer deer were killed when reflectors were uncovered (6 of the 58 killed overall) compared to when they were covered (52 of the 58 road-kills recorded). Four test sections were established along a highway (0.7–1.1 km long). Swareflex wildlife reflectors (17 × 5 cm; red) were mounted on 1-m posts, 20 m apart (10 m at bends) and 1 m from the edge of the highway. Reflectors in each section were alternately covered and uncovered at 1-week intervals during October–April from February 1981–April 1984. Intervals were extended to two week after December 1982. Alternate test sections were paired so that reflectors in each pair were covered while reflectors in adjacent sections were uncovered. Road-kills were recorded daily.

2 

A controlled study in 1984 of captive deer in Michigan, USA (Zacks 1986) found that reflectors, angled to deflect car headlight illumination into adjacent habitat, did not affect crossing rates of white-tailed deer Odocoileus virginianus. There were no significant differences in crossing rates when the route was fitted with red reflectors (256 crossings), white reflectors (200 crossings) or no reflectors (264 crossings). Ten captive-born deer were housed in a 3.5-acre pen. Five posts were installed in a line at 66-foot intervals. A pair of car headlights was aimed alongside this line. Each night, one trial each was run using no reflectors, white reflectors and red reflectors. Reflectors were fastened 42 inches up posts. All treatment orders were replicated three times. Data were collected over 18 nights, between 20 August and 6 October 1984. Trials lasted 15 minutes. Water (to attract deer) was dispensed noisily, by remote control, at five and 10 minutes, first on one side of the post line, then the other. Water ran into containers with holes, which drained in 1.5 minutes. Crossings by deer were counted by observers in concealed positions.

3 

A before-and-after study in 1977–1982 along a road through agricultural land in Illinois, USA (Waring et al. 1991) found that warning reflectors did not reduce deer-vehicle collisions. A similar number of white-tailed deer Odocoileus virginianus was killed overnight during a year with reflectors installed (six deer) as during the previous two years before reflectors were installed (5–6/year). The local deer population was reported to have decreased over this time. Behaviour of deer crossing the road or feeding at the roadside did not appear to be altered by reflectors. Eighty Swareflex wildlife warning reflectors were installed along each side of a 0.8-km section of a two-lane highway (speed limit 88 km/hour). Reflectors comprised two mirrors (5 × 17 cm) covered with red prism plates on posts 20 m apart, 3 m from the road edge. Collision data were provided by transportation personnel and direct observations.

4 

A controlled study in 1986–1989 along a highway in Wyoming, USA (Reeve & Anderson 1993) found that Swareflex reflectors did not reduce road deaths of mule deer Odocoileus hemionus. More deer were killed when reflectors were displayed (126) than when they were covered (64). During the same periods, there were 85 and 62 deer killed respectively in a control site without reflectors. After three years, only 215 (61%) of the reflectors were still in good condition. In October 1986, Swareflex reflectors were installed on both sides of a 3.2-km section of a highway (US 30). The 350 reflectors were on posts (height 61–91 cm), 20 m apart (10 m on bends) and 3 m from the road edge. Reflectors were covered and uncovered at 1-week intervals from October 1986 to February 1987 and then at 2-week intervals until May 1989. A control section (3.2 km) without reflectors was also monitored. Deer-vehicle collisions were monitored in October 1986–April 1987 (daily), November 1987–April 1988 and October 1988–May 1989 (each at 2–5-day intervals).

5 

A replicated, before-and-after study in 1980–1994 along 16 highways in Minnesota, USA (Pafko & Kovach 1996) found that reflectors reduced rural deer-vehicle collisions by 50–97%, but that collisions in suburban areas increased. Collisions were reduced by 90% along roads in the four coniferous forest areas (after installation: 2 collisions; before: 26), 79% along roads in the four ‘farmland’ areas (after installation: 9 collisions; before: 54) and 87% along roads in the four hardwood forest areas (after installation: 3 collisions; before: 25). However, collisions increased in four suburban areas (after installation: 4.4–7.3 collisions/year; before: 2.4–3.4). Swareflex brand red reflectors were installed along 16 highway sections through three different rural habitats and in a suburban area. Deer-vehicle collisions were monitored before (pre-1988) and after installation (1988–1994).

6 

A study in 1996 in a forest in Zealand, Denmark (Ujvári et al. 1998) found that fallow deer Dama dama initially responded to wildlife reflectors with alarm and flight but became habituated to the light reflection. On the first night, using a low level of lighting, deer fled from the reflection in 99% of cases. On night five, using the same light level, only 16% fled and 74% did not react. On nights 6–7 with four light levels, 86–94% fled. However, on nights 16–17 only 30–37% fled and 38–48% showed no response. Following a one-night break, deer fled almost twice as much as they did the night before the break (35–90% vs 20–54%). Feeding deer were exposed to light reflections (WEGU reflector; two sloping mirrors within a cover) at predetermined time intervals and their behavioural responses were recorded. Data were collected over 17 nights (two with no lighting used) in April 1996. Only the lowest light level was used on the first five nights. Subsequently, four levels were used.

7 

A replicated, randomized, controlled study in 1999–2005 along a highway in Indiana, USA (Gulen et al. 2000) found that wildlife reflectors reduced deer-vehicle collisions by 19% overall, but there was no difference between different reflector colours, spacing or design. When reflector sites were combined and compared with sites without reflectors, there was a 19% reduction in deer-vehicle collisions with reflector use. However, there was no significant difference in numbers of collisions between different reflector combinations (colours, spacing, single/dual design, reflectors on central reservation or not) or between each reflector combination and sites without reflectors. The greatest decrease in collisions was associated with 30-m reflector spacing regardless of colour or design. In 1999, two replicates of 16 treatment combinations (randomized order) were installed along two 1.6-km-long road sections. Treatments were different reflector colour (red and blue/green), spacing (30 m and 45 m), design (single and dual reflectors) and whether or not the central reservation also had reflectors. There was a 1.6-km control section without reflectors at each end of each replicate. Numbers of deer-vehicle collisions were recorded in April–May and October–November in 1999–2005.

8 

A before-and-after study in 1990–1998 in Tasmania, Australia (Jones 2000) found that following installation of wildlife warning reflectors, speed restrictions, reflective wildlife signs, rumble strips, wildlife escape ramps and publication of an educational pamphlet, an eastern quoll Dasyurus viverrinus population partially re-established and vehicle collisions with Tasmanian devils Sarcophilus laniarius, but not eastern quolls, decreased. Effects of the different actions were not investigated individually and results were not tested for statistical significance. Following local extinctions, 3–4 quolls re-colonised within six months of installation, increasing to ≥8 animals after two years. Road-kills for quolls were similar after implementation (1.5/year) compared to before (1.6/year), but decreased for Tasmanian devils (after: 1.5/year: before: 3.6). Following road widening in 1991, vehicle-wildlife collisions increased and quolls became locally extinct (from 19 animals). In 1996, reflective wildlife deterrents (Swareflex; 20 m intervals, 50 cm above ground) were installed, along with the other five interventions. Animals were surveyed using 60 cage traps for three nights during alternate months in October 1990–April 1993. Then, 10–20 traps were set for 20–100 trap nights in April, May and July 1995–1998. Spotlight counts were made once or twice in 1991, 1995, 1996 and 1998. Road-kills were recorded in 1990–1996.

9 

A replicated, controlled study in 2000–2003 along 10 highways in Virginia, USA (Cottrell 2003) found that warning reflectors did not reduce collisions between vehicles and deer Odocoileus sp. There was a similar rate of deer road casualties on sections with reflectors (4.6/mile/year) compared to sections without reflectors (4.8/mile/year). Deer warning reflectors (red) were installed on posts along 0.4–2.3-km sections of 10 highways (2–4 lane) from October 2000 to May 2002. Reflector sites and adjacent sites without reflectors were each monitored for 6–28 months. Deer road-kills data were collated by officials from the state Department of Transportation.

10 

A replicated, controlled, before-and-after study in 1992–2000 along roads in Michigan, USA (Rogers et al. 2004) found that wildlife warning reflectors did not reduce deer-vehicle collisions. The rate of collisions after reflectors were installed (8.5/year) was similar to that before reflectors were installed (8.2/year). This was also similar to the collision rate on another road section, at the same time, where reflectors were not installed (after: 13/year; before: 9.5/year). The total number of deer-vehicle collisions recorded was 279. In 1998, Swareflex wildlife warning reflectors were installed along three 3.2-km-long sections of road. Three additional 3.2-km-long road sections were controls with no reflectors. Collisions between 18:00 and 24:00 h, monitored by Michigan State Police, were compared before (1992–1997) and after (1998 and 2000) reflector installation.

11 

A before-and-after study in 2004–2005 at a college campus in Georgia, USA (D'Angelo et al. 2006) found that wildlife warning reflectors did not reduce white-tailed deer Odocoileus virginianus behaviours that were likely to cause collisions with vehicle. When red or blue-green reflectors were installed, there was a proportional increase in behaviours that were likely to cause deer–vehicle collisions. White or amber reflectors resulted in an increased rate both of responses that increase and that decrease collision likelihood. A total of 1,370 deer responses were recorded. A smaller proportion of animals stopped moving toward the road as a vehicle approached when reflectors were installed (red: 13%; white: 55%; blue-green: 14%; amber: 50%) compared to before reflectors were installed (64%). In two test areas (5 km apart), 15 posts were installed 15 m apart, staggered on opposite sides of the road. After two weeks, Strieter-Lite Wild Animal Highway Warning Reflectors were installed on posts (61–76 cm above road). Deer–vehicle interactions were observed using an infrared camera for four hours/night before (15 nights in November 2004–January 2005) and after installation of reflectors (January–May 2005). Two reflector colours were tested in each area for 15 nights each.

12 

A replicated, controlled study in 2006 at two grassland sites in New South Wales, Australia (Ramp & Croft 2006) found that red Swareflex wildlife warning reflectors increased the proportion of bush wallabies Macropus rufogriseus fleeing approaching lights but red Strieter-Lite reflectors and white version of both types did not affect proportions of fleeing bush wallabies or red kangaroos Macropus rufus. A higher proportion of bush wallabies fled when lights shone at red Swareflex reflectors (8%) than when lights shone without reflectors (3%). There was no such response for red kangaroos (reflectors: 3%; no reflectors: 5%). There were no significant differences in fleeing response rates for bush wallabies when lights shone at red Strieter-Lite reflectors (with: 5%; without: 3%) or at white reflectors of either type (with: 5–6%; without: 3%). There were also no significant differences in fleeing response rates for red kangaroos when lights shone at red Strieter-Lite reflectors (with: 5%; without: 7%) or at white reflectors of either type (with: 3–5%; without: 5%). In two grassland enclosures, a ‘road’ strip was mown and had 55-W lights installed in pairs every 20 m. Sequentially activating these lights mimicked approaching cars. Wildlife warning reflectors (Swareflex and Strieter-Lite) were placed on either side of the road at 20-m intervals. Over three days, animals were exposed to one night with no lights, one night with lights and no reflectors and one night with lights and reflectors. This three-day sequence was repeated 15 times and fleeing behaviour was surveyed using infrared cameras.

13 

A review of two studies in 2000–2010 in Australia (Bond & Jones 2014) found that installing wildlife warning reflectors had mixed results regarding reducing road deaths of mammals. One study showed reflectors prompted increased vigilance and flight by red kangaroos Macropus rufus. Another study showed that reflectors did not reduce the number of Proserpine rock-wallabies Petrogale persephone killed by collisions with vehicles.

14 

A replicated, randomized, controlled study in 2002–2014 in two grassland sites and five roadside areas in Germany (Brieger et al. 2017) found that wildlife warning reflectors along roads did not cause roe deer Capreolus capreolus to evade traffic more effectively. In two fenced grassland areas, there was no significant difference in successful evasion of traffic when wildlife reflectors were used and not used (data reported as model results). The same results were found in five roadside areas (data reported as model results). In two fenced grassland areas, reflectors and headlights (mimicking cars), headlights without reflectors and no reflectors or headlights were each in place for two periods of one week each. This was carried out four times between September 2012 and April 2014. The order of these combinations of reflectors and lights was varied randomly. Groups of three to six deer occupied each area. Their behaviour was monitored by infrared video cameras. At five sites, three thermal cameras were installed between June 2012 and June 2014 in trees close to roads at 3–4 m high. Between July 2012 and April 2014, wildlife warning reflectors were installed along both side of the roads. The behaviour of roe deer clearly visible in video recordings was documented.

15 

A replicated, controlled study in 2014–2017 of 151 road sites in central Germany (Benten et al. 2018) found that four types of wildlife warning reflector did not reduce wildlife-vehicle collisions. The number of vehicle collisions was similar with and without four types of wildlife warning reflectors for three groups of mammals: deer (roe deer Capreolus capreolus, red deer Cervus elaphus, fallow deer Dama dama); wild boar Sus scrofa; and other mammals (badger Meles meles, red fox Vulpes vulpes, hare Lepus europaeus/rabbit Oryctolagus cuniculus, wildcat Felis silvestris, racoon Procyon lotor). Data are reported as statistical model results. Three types of wildlife warning reflectors were installed along 151 stretches of road (average 2 km long): dark-blue reflectors (51 sites); light-blue reflectors (50 sites) and multi-coloured reflectors (50 sites). In addition, one type of reflector (transparent/silver) with an acoustic warning (1.5 second sounds triggered by vehicle headlights) was installed along a 200 m stretch of road at 10 of the 101 sites with blue reflectors. Reflectors were installed on posts (55–100 cm high) spaced 25–50 m apart. Wildlife-vehicle collisions reported to the police (1,984 in total) were analysed for 12 months with the reflectors installed and 12 months without in 2014–2017.

Referenced papers

Please cite as:

Littlewood, N.A., Rocha, R., Smith, R.K., Martin, P.A., Lockhart, S.L., Schoonover, R.F., Wilman, E., Bladon, A.J., Sainsbury, K.A., Pimm S. and Sutherland, W.J. (2020) Terrestrial Mammal Conservation: Global Evidence for the Effects of Interventions for terrestrial mammals excluding bats and primates. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.