Use chemical repellents along roads or railways

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • Five studies evaluated the effects on mammals of using chemical repellents along roads or railways. Two studies were in Canada and one each was in Germany, Norway and Denmark.



  • Survival (2 studies): Two studies (one before-and-after, one site comparison), in Germany and Norway, found that chemical-based repellents did not reduce collisions between ungulates and road vehicles or trains.


  • Behaviour change (4 studies): Two of four studies (including three replicated, controlled studies), in Germany, Canada, and Denmark, found that chemical repellents, trialled for potential to deter animals from roads, did not deter ungulates. The other two studies found mixed results with repellents temporarily deterring some ungulate species in one study and one of three deterrents deterring caribou in the other.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A before-and-after study in 1991–1996 at a research centre in Nordrhein-Westfalen, Germany (Lutz 1994) found that Duftzaun scent repellent temporarily deterred some but not all large mammal species and did not reduce vehicle collisions. Red deer Cervus elaphus, roe deer Capreolus capreolus and wild boar Sus scrofa were killed on the road. There was no significant difference between numbers killed on the road when repellent was used (18/year) compared with before (13/year) or after (9/year) use (data supplied by author). In enclosure trials, mufflon Ovis orientalis (seven animals) avoided scented posts for 15 minutes. Sika deer Cervus nippon (four) avoided posts for a few minutes and roe deer (four) approached posts cautiously. Red deer (one) and fallow deer Dama dama (four) were not deterred by repellent. Trials were held in six enclosures. Duftzaun (a mixture of 10 acids integrated into a ridged foam) was applied to tops of posts supporting 50% of daily feed and animals’ behaviours were recorded. In November 1992, a Duftzaun ‘scent fence’ was installed along a 2.8-km-long highway section where deer crossed. Scent was re-injected after four weeks and then every three months. Vehicle-wildlife collisions were recorded for two years before installation (1991–1992), three years after installation (1993–1995) and one year post-trial (1996).

    Study and other actions tested
  2. A replicated, controlled study in 1996–1998 in forest in Ontario, Canada (Castiov 1999) found that 18 scent repellents (trialled for potential to deter animals from roads) did not deter white-tailed deer Odocoileus virginianris, elk Cervus canadensis nelsoni or moose Alces alces americana. Animals used a similar proportion of trails with repellents applied (63–80%) and of trails without repellents (62–74%). Similarly, at mineral licks with repellents, there were fresh animal tracks on 59% of days, which was not significantly different to the 72% of days at mineral licks without repellents. Eighteen potential repellents were identified (from literature review) and tested on wild deer or deer, elk and moose. Repellents were mainly chemicals, including commercial repellents (Deer Away powder, Critter Ridder, mothballs) and those that simulated predators (e.g. wolf, coyote) or humans (soap, hair, clothing, sweat), but also included wolf and human silhouettes. Use of pairs of trails through snow (up to 240 pairs) with head-height repellents or without repellents, were monitored by counting tracks in winter 1997 or 1998. Repellents were also tested at a mineral lick. Use of this was monitored by track counts and an infra-red camera on days with and without repellents, in summer 1997.

    Study and other actions tested
  3. A replicated, controlled study in 1998 in three captive facilities in Alberta, Canada (Brown et al. 2000) found that one of three repellents (trialled for potential to deter animals from roads) discouraged feeding by caribou Rangifer tarandus. Animals ate significantly less food treated with lithium chloride (day 1: 900 g consumed; days 2–5: 200–300 g/day) than untreated food (1,200 g/day). Caribou ate significantly less food treated with Deer Away Big Game Repellent® on day 1 (300 g consumed) but not days 2–5 (700–900 g/day) compared to untreated food (1,200 g/day). Wolfin® did not affect the amount eaten (days 1–5: 1,100 g/day; untreated: 1,100 g/day). Lithium chloride (a gastrointestinal toxicant), Deer Away Big Game Repellent® (olfactory and taste repellent) and Wolfin® (olfactory repellent stimulating wolf urine), which could each be added to salt-sand mixtures or placed along roads to discourage salt licking, were tested on 14 captive caribou at three sites. Big Game Repellent powder (12–15 g/kg pellets) and lithium chloride (150 mg/kg body mass) were put on pelleted food. Wolfin capsules (5 cm) were placed on 1-m-high posts, 2 m from pellets. Food was provided without repellent for two days before and after a five-day period with repellents, in February–May 1998.

    Study and other actions tested
  4. A before-and-after, site comparison study in 1985–2003 along a railway through forest in Hedmark County, Norway (Andreassen et al. 2005) found that chemical scent-based repellent did not reduce moose Alces alces collisions with trains. In scent-marked areas, there was an average of 0.3 collisions/km/year when scent marks were applied compared to 1.8/km/year before. However, there was large variation in effectiveness between sections and the reduction was not statistically significant. Numbers killed/km/year in non-treated sections tended to rise over the study period (see paper for details). Along a 100-km-long stretch of railway, ten 500-m-long sections were sprayed with repellent during the winter of 1994–1995 and a further 10 in 1995–1996, during the first days when snow exceeded 20 cm depth. The repellent 'Duftzaun' (components from brown bear Ursus arctos, wolf Canis lupus, lynx Lynx lynx and humans) was sprayed on trees and bamboo canes at 5-m intervals. One treatment lasted 3–4 months. Sections without treatment (total 49 km) were also monitored. Moose-train collisions were recorded from July 1985–April 2003.

    Study and other actions tested
  5. A replicated, controlled, before-and-after study in 2006 in a conifer plantation in Denmark (Elmeros et al. 2011) found that repellents, Mota FL and Wolf Urine (trialled for potential to deter animals from roads), did not reduce visits by deer. Roe deer Capreolus capreolus visited a similar number of Moto FL-treated plots after application (6–8 plots/day) and before (4–8 plots/day). Visit rates to untreated plots were similar after application in treatment plots (7–8 plots/day) compared to before (5–8 plots/day). The same pattern held for red deer Cervus elaphus treatment plots (after: 1–3 plots/day); before: 0–4 plots/day) and untreated plots (after: 2–4 plots/day; before: 0–3 plots/day). Roe deer visited a similar number of Wolf Urine-treated plots after application (7–9 plots/day) and before (7–9 plots/day). Visit rates to untreated plots were similar after application in treatment plots (6–9 plots/day) compared to before (6–9 plots/day). The same pattern held for red deer treatment plots (after: 1–4 plots/day; before: 1–3 plots/day) and untreated plots (after: 0–4 plots/day; before: 0–4 plots/day). Eighteen sand arenas (4 m diameter, ≥400 m apart) included nine for repellent treatments and nine controls. Arenas were baited with beet and maize every 3–4 days or as required, for two months. Deer tracks were monitored daily for seven days before repellent was sponged onto four scent posts at each treatment arena. Track monitoring continued for seven further days. Mota FL was assessed from 7–21 February 2006. Repellent posts were then cleaned with alcohol and Wolf Urine assessed from 8–22 March 2006.

    Study and other actions tested
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.

Where has this evidence come from?

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Terrestrial Mammal Conservation

This Action forms part of the Action Synopsis:

Terrestrial Mammal Conservation
Terrestrial Mammal Conservation

Terrestrial Mammal Conservation - Published 2020

Terrestrial Mammal Conservation

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