It is important to know how long the interventions used to protect livestock from carnivores remain effective. The effectiveness of interventions tends to go down over time as carnivores become habituated.
We analyzed published data on the duration of the effectiveness of deterrents (chemical, acoustical, physical and mixed), electric fences, guarding animals, calving control, supplemental feeding, fences and herding against mammalian predators. We found that electric fences and calving control stay most effective for the longest time (3 months to 3 years), whereas the impact of deterrents and guarding animals lasts only up to 5 months or so.
Effectiveness was measured as the relative risk (RR), which was transformed to the percentage of damage reduction (DR) for easy interpretation. The formula is simple: DR = (1-RR)*100%. RR is the probability of damage when an intervention is applied divided by the probability of damage without an intervention. The formula of the relative risk is also simple: RR = (nt/Nt)/(nc/Nc), where nt is the number of losses (livestock, beehives, etc.) with the intervention, Nt is the total number of the resource with the intervention (livestock, beehives etc.), nc is the number of losses without the intervention and Nc is the total number of resource without the intervention. The letter "t" stands for treatment (with intervention) and "c" for control (without intervention).
Interventions are effective when RR is less than 1, ineffective at RR = 1 and counter-productive (interventions produce more damage) when RR is higher than 1. Interventions are most effective when RR = 0, i.e. no losses are inflicted when the intervention is applied (nt = 0).
Search of literature, data collection and analysis
CONDITIONS OF SUCCESS
Intensive search for literature
Use of suitable and reliable metrics, like relative risk, to quantify the effectiveness
Understanding of local details in intervention applications that need particular attention