Individual study: A 33-week trial to test the efficacy of an ultrasonic device in deterring domestic cats from entering gardens in the UK
Nelson S.H. Evans A.D. & Bradbury R.B. (2006) The efficacy of an ultrasonic cat deterrent. Applied Animal Behaviour Science, 96, 83-91
Although, the impact of domestic cat predation on wildlife in the UK is unknown, many studies show that they kill large numbers of wild birds and small mammals. In addition, cats are often seen as a nuisance by non-cat owners because of their habit of defaecation in flower and vegetable beds. For non-cat owners in the UK, deterrent devices offer the only practical solution to keeping cats out of gardens. Various commercial cat deterrents are available from cheap chemical sprays and pellets to more expensive equipment, such as ultrasonic devices. However, there are very few published field experiments of effectiveness of these devices. Field trials were therefore undertaken to test the efficacy of a commercially available ultrasonic cat deterrent in the UK.
Ultrasonic device: The device tested, ‘CatwatchTM’, works by detecting movement and body heat within a range of 12 m, through an angle of 100º. Upon detection an ultrasonic alarm is triggered operating at a frequency of 21-23 kHz and a volume of 96 db at 1 m, declining to 44 db at 13 m. It is claimed to be effective in scaring cats up to this distance. Trials of a similar device concluded that there was no threat to cat welfare (Mills et al. 2000). Results from an earlier test indicated that the deterrent effect increases with time. Therefore, an experiment designed to investigate interactions between device effect and length of time of deployment was undertaken.
Experimental design: Trials used volunteer observers, half given a working device and half one that had been disabled. Volunteers were told that some of the devices had been disabled but did not know which. They were asked to set up the device in accordance to the manufacturers’ instructions i.e. mounted on the plastic stake supplied or on a wall, so that the heat/motion detector lens was 20 cm above ground level. No advice was given as to where in a garden it should be located. The likely average effect of the device as used by the public, rather than the maximum effect that could be achieved through strategic positioning of the device e.g. at entry points most frequently used by cats, was therefore tested.
Volunteers throughout the UK were selected to participate if they had an average (100-450 m²) sized, suburban garden, did not already deploy a deterrent and experienced more than five cat visits per week. Initially 150 volunteers entered into the trials. The experiment ran for 33 weeks in 2003. Entry into the experiment was staggered from March to May (and ended in October 2003) to control for any seasonal variation in cat activity. Some volunteers dropped out, resulting in a total of 96 observers (Table 1, attached). Volunteers were asked to make three 30 min observations each week, one in the morning (between 07:30 and 10:30 h), one in the middle of the day (between 10:30 and 13:30 h) and one in the afternoon (between 13:30 and 16:30 h). In practice, some made fewer observations, while others made more (ranging 1 to 6 observations/week), but there was no bias between active and disabled devices in the observations carried out. During each observation period, whether a cat entered their garden and the duration of each visit was recorded.
Deploying an active Catwatch resulted in a small (but not statistically significant) reduction in the probability of a cat entering the garden. The interaction between device activity and time was not significant nor was there a significant effect of device activity when controlling for week. However, there was a significant effect of week when controlling for device activity.
The interaction between device activity and time was statistically significant. Average durations of cat presence per observation period, broken down into the early (weeks 1-17) and late (weeks 18-33) of the experiment were:
0.72 min and 0.96 min (S.E. 0.24) for disabled devices;
0.73 min (S.E. 0.17 min) reducing to 0.57 min (S.E. 0.14) for active devices. The average duration of intrusions was therefore reduced by about 22% in these gardens.
Conclusions: This study demonstrates that ‘CatwatchTM’ had a moderate deterrent effect and thus offers a partial solution to householders wishing to exclude cats from their gardens. Both measures of deterrent effect appeared to increase with time, suggesting that cats were learning to avoid gardens with active devices, rather than becoming habituated to them. It is possible that the deterrent effect could be improved by deploying multiple devices, and careful siting at the most frequently used entry points by cats to gardens.
Mills D.S., Bailey S.L. & Thurstans R.E. (2000) Evaluation of the welfare implications and efficacy of an ultrasonic ‘deterrent’ for cats. Veterinary Record, 147, 678–680.
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