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Providing evidence to improve practice

Action: Use lights and sound to deter crop damage by mammals to reduce human-wildlife conflict Terrestrial Mammal Conservation

Key messages

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  • Two studies evaluated the effects of using both lights and sound to deter crop damage by mammals to reduce human-wildlife conflict. Both studies were in the USA.





  • Human-wildlife conflict (2 studies): Two replicated paired sites, controlled studies (one also randomized), in the USA, found that frightening devices, emitting lights and sound, did not reduce crop intrusions by white-tailed deer or food consumption by elk and mule deer.

Supporting evidence from individual studies


A replicated, paired sites, controlled study in 1999 of corn fields at two sites in Nebraska, USA (Gilsdorf et al. 2004) found that a device emitting lights and sound (Electronic Guard) did not reduce crop visits by white-tailed deer Odocoileus virginianus. The number of deer visits/km of field boundary did not differ between treatment fields protected by Electronic Guards (38–46/day) and unprotected control fields (40–56/day). Similarly, there was no difference between fields before devices operated (treatment fields: 24 visits/km/day; control fields: 21 visits/km/day) or after operations ceased (treatment fields: 47 visits/km/day; control field: 53 visits/km/day). Four groups of fields were studied at each of two sites. Fields were 0.5–2.5 km apart and separated by woodland. In each group, one field was protected by two Electronic Guard devices and one field was unguarded. Electronic Guards comprised a strobe light (60 flashes/minute) and siren (116 dB at 1 m). They operated at night, from when corn crops became susceptible to damage (13 July 1999 at one site and 25 July 1999 at the second site), for 18 days. Deer activity was assessed by counting tracks twice while devices operated, once during the two weeks before devices operated and once during the week after they operated.


A replicated, randomized, paired sites, controlled study in 2001 of pastures on a ranch in Colorado, USA (VerCauteren et al. 2005) found that a device emitting lights and sound (Critter Gitter™) did not reduce combined elk Cervus canadensis and mule deer Odocoileus hemionus food consumption. Daily alfalfa consumption at bales protected by Critter Gitters™ (3.1–6.0 kg/day) did not differ from that at unprotected bales (2.8–7.3 kg/day). The Critter Gitter™ activated when infrared sensors detected movement and heat. When activated, an alarm (approaching 120 decibels) sounded for five seconds and a pair of red LEDs flashed. Five sites (>300 m apart) on private ranchland, adjacent to residential areas, were studied. Each site had two alfalfa bales, 60 m apart. One or two devices were positioned by one bale (selected randomly). The other bale was unprotected. Devices detected animals ≤2 m away. Alfalfa consumption was estimated visually, every two or three days, on 10 occasions.

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.