Variables Affecting Ultrasound Repellency in Philippine Rats

Three ultrasonic devices (20, 20-30, and 40 kHz) were tested for effectiveness in repelling Philippine rats (Rattus rattus mindanensis) under 3 sets of test conditions (i.e., plentiful vs. restricted food supply, native vs. immigrant rats, and continuous vs. discontinuous ultrasound). Food consumption was significantly reduced for all devices under the plentiful-food condition. With restricted food, only the 20-30and 40-kHz devices reduced feeding. Immigrant rats (animals preadapted to living adjacent to the ultrasound test chambers) showed a high avoidance of the new sound-chamber areas including the control (no ultrasound), making the test insensitive. Native rats (animals preadapted [confined] to the chambers before exposure to the ultrasound devices) showed significant avoidance of food in 3 test chambers containing the ultrasound devices, especially the 20-kHz unit. A 2nd repellency measure (rat photocell breaks per day) yielded a similar index of efficacy for the 3 devices. The 20-kHz device produced the lowest photocell-break activity during the native-rat condition. A 30-dB reduced-intensity trial yielded no rat activity effects for any of the devices. Efficacy of the devices was therefore highly dependent upon ultrasonic frequency, intensity, and the preexisting rodent-infestation condition. J. WILDL. MANAGE. 46(1):148-155 Since the first demonstration that rodents were capable of emitting ultrasound (Anderson 1954), many studies have indicated that ultrasonic frequencies may be used for communication in Rodentia (Sales and Pye 1974). Ultrasonic cries can be elicited in Norway rats (Rattus norvegicus) by cold stress or electric shock (Noirot 1972, Bell et al. 1974), isolation of rat pups (Allin and Banks 1972), or handling (Anderson 1954). High-frequency sounds in the range of 20-50 kilohertz (kHz) are also produced by Norway rats during courtship (Sales 1972b), after mating (Barfield and Geyer 1972), and during aggressive encounters (Sales 1972a). High-intensity sound at 120-150 decibels (dB) has been used to produce audiogenic seizures and death in both laboratory and wild Norway rats (Morgan and Gould 1941), but such sound levels may damage the human ear, and wild rats are not as susceptible as laboratory strains (Sprock et al. 1967). Although ultrasound can elicit alarm response in rats in certain situations, there is no firm evidence that ultrasound is noxious to rats. Only 1 report (Belluzzi and Grossman 1969) indicates that ultrasound may sometimes be as effective as electric shock in producing avoidance in rats. This report indicated that albino rats would reliably avoid the onset of 20-30kHz ultrasound by making an escape response in the presence of a cue light. Several commercial ultrasonic devices for repelling rats and mice have been marketed for food-storage warehouses, grain elevators, and other facilities where the use of rodenticides may be impractical. These devices are not ordinarily used in combination with lethal rodent control, but manufacturers often recommend that materials that attract rats (harborage, spilled food, and water) be removed when the units are installed. The conditions under which these devices produce their maximum effects have not been investigated. For example, we can hypothesize that food-deprived, resident rats that have been continuously 148 J. Wildl. Manage. 46(1):1982 This content downloaded from 207.46. 13.129 on Wed, 29 Jun 2016 04:23:10 UTC All use subject to http://about.jstor. org/terms ULTRASOUND REPELLENCY IN RATS* Shumake et al. 149 exposed to ultrasound should be extremely difficult to repel. In this report, we evaluate the repellent efficacy of 3 devices (20, 20-30, and 40 kHz) under each of 2 levels of food availability, living-space familiarity, and ultrasound continuity. Comparisons of repellent efficacy for each set of conditions allow acceptance or rejection of the above hypothe-