Electronic rodent repellents are advertised as safe, ethical and environmentally friendly alternatives to traditional control measures, such as baits and traps. Commercialised devices typically use one of three mechanisms (electromagnetic, ultrasonic, or ionic emissions) to repel rodents and other common pests. Electromagnetic devices use electric and magnetic fields to create vibrations (electromagnetic waves) at varying rates (frequencies) designed to disrupt and repel rodent invaders. Electromagnetic waves are reportedly picked up as vibrations by rodents, disrupting their attempts to forage for food, build nests and communicate with one another. However, there is a lack of scientific evidence showing that devices of this type are measurably effective at fulfilling these claims (Howard and Marsh, 1985). Therefore, electromagnetic rodent control devices should be viewed with considerable scepticism by regulators and consumers (Bomford and O’Brien, 1990).
Ultrasonic devices emit high-pressure sound waves at frequencies beyond the limit of human hearing but audible to pests such as rats and mice. High-intensity ultrasonic sound has been shown to elicit flight responses in rats; these devices were once heralded as promising rat repellents (Pinel, 1972 and 1974). However, multiple published studies discredit the practical application of ultrasound as a viable rodent control method (Shumake et al., 1982; Howard and Marsh, 1985; Monro and Meehan, 1987). Any observations of efficacy are generally short-lived because rodents quickly adjust to the sound in a process called habituation (Bomford and O’Brien, 1990; Clapperton, 2006) or learn to avoid the source of the offending noise stimulus altogether. Furthermore, there are issues with the practical application of these devices. Ultrasonic waves cannot pass through solid objects or turn around corners, and commercial units have a short active range. Use of these devices is best suited to corridors and unobstructed areas that allow sound waves to be propagated freely. Therefore, many devices would be needed to cover an entire poultry operation, which limits the viability of agricultural application of this technology.
Ionic devices emit negatively charged atoms, similar to those produced naturally in the atmosphere before a lightning storm. Animals, which are naturally sensitive to these negatively charged ions, supposedly become confused and frightened and, as a result, seek shelter beyond the range of these devices. While there is limited peer-reviewed research demonstrating that these devices reduce the burden of rodents, ionisation has been shown to reduce airborne transmission of dust, ammonia and pathogenic bacteria, such as Salmonella, in poultry operations (Holt et al., 1999; Mitchell et al., 2002; Mitchell et al., 2004). It should be noted that this research involved the use of large-scale electrostatic space charge systems (ESCS) rather than the small commercial ionising units marketed specifically for rodent control.
Other rodent control measures include the electronic monitoring of rodent activity. Devices are typically small battery-powered units that use motion and temperature sensors to identify the presence of rodents. The ability to accurately monitor on-farm rodent activity enables producers to identify hotspots and to implement targeted control, improving outcomes and minimising damage. This technology could also be used to assess the efficacy of current control strategies by observing changes in rodent activity. However, because of their limited detection range, it might not be practical to use these devices to assess rodent activity throughout an entire poultry operation. To counteract this, producers are recommended to use data from a range of measures to assess the effectiveness of rodent control strategies. These might include electronically tracked rodent activity as well as visual observations of rodents, bait intake, and other signs of activity (e.g. droppings, nests, structural damage).
