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Deterrent or dinner bell? Alteration of badger activity and feeding at baited plots using ultrasonic and water jet devices
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Applied Animal Behaviour Science 115 (2008) 221–232 www.elsevier.com/locate/applanim
Deterrent or dinner bell? Alteration of badger activity and feeding at baited plots using ultrasonic and water jet devices Alastair I. Ward *, Ste´phane Pietravalle, David P. Cowan, Richard J. Delahay Central Science Laboratory, Sand Hutton, York YO41 1LZ, UK Received 6 November 2007; received in revised form 28 May 2008; accepted 4 June 2008 Available online 16 July 2008
Abstract The increasing incidence of reports of damage caused by Eurasian badgers (Meles meles) in UK urban environments requires the development of effective, humane, non-lethal solutions. Ultrasonic deterrents are widely available to the public and are sold as a humane solution to the presence of unwanted animals in urban gardens. The reported failure of some ultrasonic devices may be caused by habituation of target animals to the devices and the lack of association with a negative, physical stimulus. We tested the ability of a commercially available, motion sensor-triggered ultrasonic device and a motion sensor-triggered water jet device, alone and in combination, to alter badger activity and feeding at baited plots. The ultrasonic device, whether used alone or in combination with the water jet, was associated with significantly higher badger activity at baited plots in comparison to control plots, and bait consumption was higher when the ultrasonic device was used alone. When the water jet was used alone, bait consumption was significantly reduced in comparison to control plots, but badger activity was not. There was no evidence to suggest that aversion to the ultrasonic device could be reinforced by the water jet, but some evidence to suggest that ultrasonic devices may have attracted badgers to baited plots. While the effects of the water jet on bait consumption were statistically significant, they were also very small (a 12% difference between the treatment and control fitted means). We conclude that neither device, used alone or in combination, present effective solutions to the growing problem of urban badger damage. Crown Copyright # 2008 Published by Elsevier B.V. All rights reserved. Keywords: Eurasian badger; Area repellent; Ultrasound deterrent; Urban garden; Water jet deterrent
* Corresponding author. Tel.: +44 1904 462077; fax: +44 1904 462111. E-mail address: [email protected] (A.I. Ward). 0168-1591/$ – see front matter. Crown Copyright # 2008 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.applanim.2008.06.004
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1. Introduction Increasing interest in non-lethal approaches to resolving human–wildlife conflicts requires the development and evaluation of novel techniques. Cases of physical damage to property and infrastructure caused by Eurasian badgers (Meles meles) are relatively common within the UK (Wilson and Symes, 1998; Mathews and Wilson, 2005; Delahay et al., in press) and have been recorded elsewhere in Europe (Balestrieri and Remonti, 2000). Reports of badger-related problems in urban areas of the UK have increased in recent years (Delahay et al., in press). These problems typically comprise either the undermining of property (i.e. buildings and other structures) during badger sett (underground burrow) construction, or digging damage to gardens. These problems are currently dealt with using non-lethal methods such as the exclusion of badgers from the problem sett (Harris et al., 1994; Mathews and Wilson, 2005; Central Science Laboratory, 2007). The badger is a protected species in the UK, thus any action requiring interference with badgers themselves, or their setts requires a licence from the appropriate statutory Government agency under the Protection of Badgers Act 1992. However, sett exclusions can be problematic, and suffer a high failure rate, particularly when the aim is the closure of a main sett in an urban area (Delahay et al., in press). Development of an effective area deterrent could provide a useful tool to aid exclusions and to deter badger activity in areas susceptible to damage. Chemical feeding deterrents have been used against badgers with some success (Baker et al., 2005a,b) but these only prevent consumption of food that animals have been conditioned against, and do not repel them from the area containing the food. Electric fencing has also been used successfully to exclude badgers from crop fields (Wilson, 1993; Poole and McKillop, 1999) and farm buildings (Tolhurst et al., in press), but in urban gardens, health and safety considerations and maintenance requirements limit its applicability. Ultrasonic deterrents are widely available to the public as a putatively humane, cost-effective and easy alternative to lethal control of wild animals (Bomford and O’Brien, 1990). However, studies of the effectiveness of such devices report ambiguous results. Nelson et al. (2006) observed a decrease in the frequency and duration of visits by domestic cats to urban gardens when motion sensor-triggered ultrasonic deterrents were actively emitting a signal of 21–23 kHz at 96 db at 1 m. Shumake et al. (1982) found that three ultrasonic devices emitting constantly at 20, 40 and 20–30 kHz at 118, 116 and 103 db at 30 cm, respectively, all deterred Philippine rats (Rattus rattus mindanensis) from feeding at baited points. Conversely, Mills et al. (2000) could not repel domestic cats from an area using an ultrasonic device emitting a signal of 19– 30 kHz at 100 db at 1 m. In addition, Bender (2003) did not observe altered behaviour or reduced site occupancy among eastern grey and red kangaroos (Macropus giganteus and M. rufus, respectively) in response to two ultrasonic devices emitting signals of 17–27 kHz at 70 and 35 db at 50 m. Edgar et al. (2007) reported a similar failure to inhibit dingo (Canis lupus dingo) activity at baited plots using an ultrasonic device emitting at 24–25 kHz at 82 db (measured directly in front of the device). Bomford and O’Brien (1990) concluded that, at best, ultrasonic deterrents might provide short-term, transient benefits. Nevertheless, such devices continue to be sold by a large number of suppliers, although claims of their efficacy have yet to be tested for a wide range of species. Indeed, until recently, the efficacy of ultrasonic deterrents had not been reported against any wild canids (Edgar et al., 2007). Although there appears to be no published information on their effectiveness against wild mustelids, these devices have been employed by the public in the UK with the intention of deterring badgers from their property.
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Failure of some ultrasonic devices to promote area deterrence is likely to be largely due to four factors. Firstly, if animals are highly motivated, such as by extreme hunger, it is unlikely that ultrasound will deter them from feeding (Shumake et al., 1982). Secondly, the ultrasound signal may be out with the hearing range of the target species. Thirdly, devices may emit with insufficient sound pressure (130 db is generally regarded as sufficient to cause discomfort and/or pain), in which case, the device may act as a signal, but not a repellent. Finally, habituation of animals to emitted ultrasound may reduce the efficacy of such devices over time (La Voie and Glahn, 1977; Shumake et al., 1982). When the device acts as a signal, or when animals have become habituated to it, encouraging them to associate the ultrasound with an aversive stimulus may enhance its effectiveness. However, behavioural reinforcement of ultrasound with an aversive stimulus has yet to be reported to our knowledge. We aimed to test the efficacy of a commercially available ultrasonic deterrent, both alone and reinforced with a commercially available water jet device, in terms of its ability to alter badger activity and bait consumption at baited plots. 2. Methods A replicated experiment was undertaken to determine whether a motion sensor-triggered ultrasonic device and a motion sensor-triggered water jet device, alone and in combination, could deter badgers from feeding on peanuts at bait stations. Both items were commercially available products, marketed to keep unwanted cats and other animals out of gardens. The manufacturer claimed that the ultrasonic device could protect areas up to 5.5 m2. Water jet devices were intended to be connected to a mains water supply. However, due to this experiment being undertaken in a rural area where no mains water was available, water jet devices were coupled using plastic hose pipes to 50 l plastic water tanks raised above the device either by placing the tank uphill of it or by raising the tank on a scaffold platform. This allowed water to flow under the force of gravity and produced sufficient pressure to eject a jet of water horizontally at a maximum height of 50 cm, with a total volume of 400–450 ml, 5–10 m from the device when activated. The jet of water was sprayed for 4 s over an arc set to 908 so that bait stations would be covered in water when activated. Ultrasonic devices were powered by one 9v PP3 cell each. The sound pressure level (SPL) of the ultrasonic device was measured in an anechoic chamber at 1 m distance using a 1/4 in. air dilatory microphone attached to an oscilloscope via a preamplifier. Measurements from the oscilloscope (in volts) were converted into SPL (in decibels) by calibration against a calibration device emitting at a known SPL. The frequency and energy of ultrasound emissions was measured at approximately 5 m distance using a Pettersson D1000X time expansion ultrasound detector (Pettersson Elektronic, Uppsala, Sweden). Three sites close to Woodchester Park on the Cotswold escarpment of Gloucestershire, UK were chosen on the basis that each was close to an active main badger sett where badgers had prior experience of foraging on peanuts. Badgers at these sites were known to visit farm buildings to forage on stored feed (Garnett et al., 2002; Ward et al., in press). At each site, four plots were established equidistant to the sett and with 100 m between them. At each plot four plastic bowls were buried flush with the ground, in a square pattern and each bowl was covered with a stone paving slab weighing approximately 4 kg, to prevent species other than badgers from accessing the bait. All bowls were filled with 150 ml of peanuts. Each plot was surrounded with 8 m of single strand electric fencing (to prevent interference by cattle but allowing free entry and exit to badgers) and also contained a water jet device, an ultrasonic device and a motion sensor-triggered digital trail camera (DS-04IR, Penn’s Woods Products Inc., Pennsylvania, USA) to monitor activity. These had previously been independently assessed as the most suitable model for indexing animal activity, from six different models of trail camera (Central Science Laboratory, unpublished data). Trail cameras were set to take photographs under infrared illumination, and record the time and date on each photograph, between dusk and dawn at 1-min intervals when motion was detected within the plot. It was not possible to determine the number of badgers visiting each plot, or to identify individual badgers from photographs. Instead, the number of badger photographs per plot per night was taken as an index of badger activity.
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The experiment was organised into three phases. During phase 1 plots were baited and monitored with no treatments allocated, in order to allow badgers to become familiar with feeding at baited plots. The phase was ended when bait consumption was observed at every plot for three consecutive nights. During phase 2 treatments were randomly allocated to each plot per site and monitoring undertaken as before, but for 14 nights. During phase 3, treatments were purposively switched between sites and monitoring undertaken as before. The treatments were (a) ultrasonic device active, (b) water jet device active, (c) both ultrasonic and water jet devices active (combined treatment) and (d) control (no equipment active) (Table 1). Treatments were not randomly switched between phases 2 and 3 because of data considerations and in order to address specific questions. The water jet treatment was removed from the experiment at the end of phase 2 because differences between it and the other treatments were already apparent. In contrast, potential effects of the ultrasonic treatment were not apparent at the end of phase 2, and so replication of this treatment was enhanced by replacing the water jet treatment with the ultrasonic treatment, as well as maintaining it at the same plots as during phase 2, to investigate longer-term effects. This yielded twice as many plots under the ultrasonic treatment during phase 3 than during phase 2. Finally, whether badgers could be conditioned against the ultrasonic treatment, during phase 3, by combining it with the water jet treatment during phase 2, was considered of applied significance. Conversely, we considered it unlikely that badgers would be conditioned against the water jet by the ultrasonic within the combined treatment during phase 2, hence did not consider it worthwhile to follow the combined treatment in phase 2 with the water jet treatment alone in phase 3. Phase 3 was ended when it became apparent that no further treatment effects were likely to be observed (i.e. little or no variation in bait consumption). Monitoring consisted of recording how many bowls had been disturbed and measuring the volume of peanuts left per bowl and per plot each morning. In addition, the number of photographs taken of badgers by the trail cameras, were used to describe the relative frequency of visits to plots (a measure of activity). Bowls were replenished with peanuts to maintain bait volumes at 150 ml on each day of the experiment. Paving slabs were then replaced over the bowls and gaps resulting from badger digging were in-filled with earth to prevent access by other wildlife. 2.1. Statistical analysis Data were analysed using GenStat 9 (VSN International, Hemel Hempstead, UK). Initially, response variables were the volume and proportion of bait consumed per bowl, and the number of badger photographs taken by trail cameras per night per plot. Treatments were analysed as two sets of explanatory variables: ‘direct treatments’ and ‘combination of treatments’. ‘Direct treatments’ assumed independence of treatment effects between phases, irrespective of the treatment that had been applied at each plot during the previous phase, and was intended to identify gross treatment effects. For the ‘combination of treatments’ analysis no such assumption was made, instead this approach tested whether treatment effects were dependent on the sequence in which they were applied. Treatment combinations were analysed as discrete units. Hence, there were four different treatments: C–U–U, C–W–C, C–WU–U, C–C–WU, where C = control, U = ultrasonic Table 1 Experimental design to test the effectiveness of an ultrasonic device and a water jet device at preventing badgers feeding at baited plots Plot
1 2 3 4
Site 1
Site 2
Site 3
Phase 2
Phase 3
Phase 2
Phase 3
Phase 2
Phase 3
U W WU C
U C U WU
U C WU W
U WU U C
U WU W C
U U C WU
U = ultrasonic, W = water jet, WU = ultrasonic and water jet, C = control (i.e. no treatment).
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device active, W = water jet device active, and WU = water jet and ultrasonic devices active, and where the first letter refers to the treatment applied during phase 1, the second letter(s) to phase 2 and the third to phase 3. Potential differences between sites were accounted for as a random term in all analyses. For bait consumption a generalised linear mixed model was used with a logit transform to account for the binary nature of the data (see below). The number of badger photographs per plot per night was analysed using a simpler restricted maximum likelihood model since there was no evidence of data departure from normality. The position of bowls and plots remained constant throughout the experiment. However, since different badgers may have consumed bait at a given plot between nights, and in consideration of the limited variability in response data between treatments, data from the same plots and bowls were not treated as repeated measures during analysis. Data were analysed from all phases, and, under separate analyses, data from phase 1 were excluded in order to avoid potential effects on control data of badger naivety to bait stations. During all analyses statistical significance was inferred at the 5% level.
3. Results Ultrasonic devices were emitting frequencies from approximately 15–30 kHz, with strong emissions cycling in the range 23–25 kHz. Peak energy was recorded at 23 kHz. The SPL of emissions was 138 db at 10 cm and 118 db at 1 m. Assuming equivalence to sound audible to humans, this would correspond to an SPL of 78 db at 100 m, however, atmospheric attenuation would considerably reduce this. Ultrasound was emitted for 5 s from detection of movement with a 30 s delay until the device could activate again. Bowls containing bait were uncovered, the contents consumed and photographs taken by trail cameras during all experimental phases at two of the three sites. At the third site, despite close proximity to an active sett, no badger activity was recorded at baited plots and the site was excluded from further analysis. At the two active sites, across all phases, bowls were uncovered on 793 of 864 bowl.nights. All the bait had disappeared (presumed eaten by badgers) in all but 11 instances where bowls had been uncovered by badgers, and on four such occasions no bait was consumed. Consequently, and since other species may have consumed left-over bait once bowls were uncovered by badgers (see below), we analysed bait consumption as a binary response: some bait consumed/no bait consumed. Of 2063 photographs, 1626 were taken of badgers, 52 of domestic cattle (at the edge and outside of plots), 24 of foxes (Vulpes vulpes), 11 of rabbits (Oryctolagus cuniculus), 12 of roe deer (Capreolus capreolus, at the edge and outside of plots), two of pheasants (Phasianus colchicus), one of a crow (Corvus corone) and one of a kestrel (Falco tinnunculus) at bait plots. A further 334 photographs either contained images of people or vehicles travelling close to the plots, or the agent triggering the cameras was not apparent. Some of the animals photographed, other than badgers, may have consumed bait from plots uncovered by badgers. However, it was considered highly unlikely that any species of wildlife other than badgers would have moved the paving slabs, and also that badgers would generally have consumed at least some bait after opening a bowl. Consequently, photographs of animals other than badgers were excluded from analysis, but data were retained from plots on nights during which other species were photographed. Among photographs of badgers, 1264 were of single animals, 279 of a pair, 68 of three animals, 11 of four animals, and four of five animals. The number of badger photographs at a plot on a given night varied from 0 to 107. From 166 plot.nights when photographs were taken, only a single photograph was taken on 24 plot.nights, on 53 plot.nights between two and ten photographs were taken, on 75 plot.nights between 11 and 50 photographs were taken and on 14
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Table 2 Effects of the sequence of treatments on the relative frequency of bait consumption at baited plots Treatment
Phase
% nights where bait was consumed
C–W–C
1 2 3
49 76 100
C–U–U
1 2 3
78 100 100
C–WU–U
1 2 3
85 100 98
C–C–WU
1 2 3
70 100 91
Data are pooled across sites.
plot.nights more than 50 photographs were taken. Photographs were taken at different plots within the same site, at the same time, on the same date on 78 occasions. On 129 occasions photographs at the same site and on the same date were taken at different plots within 1 min of each other. There was some evidence that badgers became habituated to feeding at plots with time. At all plots, including controls, bait was consumed more frequently during phases 2 and 3 than during phase 1 (Table 2). Moreover, during phase 1, the number of nights since the start of monitoring was significantly associated with the likelihood of a plot being uncovered by badgers (logistic regression, Wald = 19.226, d.f. = 1, P < 0.001). During nights 3, 4 and 5 of phase 1, bait was consumed at every plot, and so the phase was ended. Bait consumption at plots varied very little during phase 3 (Table 2), which was ended after eight nights. Irrespective of whether data were analysed directly, as a sequence of treatments or including or excluding phase 1 data, no site effect was evident but the treatment effect was significant (Table 3). When analysed directly and including phase 1 data, the water jet treatment was associated with a significantly lower probability of bait consumption than all other treatments, Table 3 Effects of treatments and sites on the likelihood of bait consumption and activity at baited plots Treatments analysed
Explanatory variable
Phases included
Site effect Variance component
Directly
As combinations
Treatment effect S.E.
Wald
d.f.
P
Bait consumption
1, 2, 3 2, 3
0.06 0.02
0.13 0.12
28.57 38.76
3 3
<0.001 <0.001
Activity
1, 2, 3 2, 3
1.44 8.49
3.14 13.41
18.93 9.85
3 3
<0.001 0.020
Bait consumption
1, 2, 3 2, 3
0.05 0.01
0.12 0.09
27.66 20.20
3 3
<0.001 <0.001
Activity
1, 2, 3 2, 3
1.44 8.52
3.14 13.41
17.30 15.66
3 3
<0.001 <0.001
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Fig. 1. Back-transformed fitted means and 95% confidence intervals for the probability of bait being consumed under each of three treatments and a control. Data are from all three phases.
including the control. In contrast, the ultrasonic treatment was associated with a significantly higher probability of bait consumption than controls, but the combined treatment did not differ significantly from controls (Fig. 1). Under these same conditions badger activity was significantly higher under the combined treatment and the ultrasonic treatment (which did not differ significantly from each other) than the water jet treatment and the control (Fig. 2). Analysed directly, and excluding phase 1 data, the water jet treatment was still associated with a significantly lower probability of bait consumption than the ultrasonic or combined treatments. However, all bait was consumed from all control plots during phases 2 and 3, so no statistical comparisons were possible between treatments and controls due to invariability in data from control plots. With phase 1 data excluded, the combined treatment was associated with significantly higher badger activity than the controls, but the water jet and ultrasonic treatments were not significantly different from controls. Activity under the water jet treatment was significantly lower than the ultrasonic and combined treatment. Differences under the water jet treatment were significant in spite of 36% fewer observations than the combined treatment, due the water jet treatment not being repeated during phase 3. When analysed as serial combinations of treatments and including phase 1 data, C–W–C was associated with a significantly lower probability of bait consumption and badger activity than all other treatment combinations, which were not significantly different from each other (Figs. 3 and 4). Excluding phase 1 data badger activity was still significantly lower under the C–W–C treatment than all other treatment combinations and the probability of bait consumption was significantly lower than the C–WU–U and C–C–WU treatments, but the lack of variation in bait consumption under the C–U–U treatment precluded statistical comparison. Nevertheless, this lack of variation was due to all bait being consumed under this treatment sequence during phases 2 and 3.
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Fig. 2. Fitted means and 95% confidence intervals for the number of photographs of badgers taken per night under each of the three treatments and controls. Data are from all three phases. The error bar to the extreme left of the graph is the least significant difference (at P = 0.05).
Fig. 3. Back-transformed fitted means and 95% confidence intervals for the probability of bait being consumed under each of the four treatment combinations. Data are from all three phases.
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Fig. 4. Fitted means and 95% confidence intervals for the number of photographs of badgers taken per night under each of the four treatment combinations. Data are from all three phases. The error bar to the extreme left of the graph is the least significant difference (at P = 0.05).
4. Discussion Emission frequency and intensity are important factors determining the likely efficacy of ultrasonic devices (Shumake et al., 1982). Fay (1988) reported that domestic dogs can hear in the range of 67–45,000 Hz, racoons (Procyon lotor) from 100 to 40,000 Hz and domestic ferrets (Mustela putorius furo) from 160 to 44,000 Hz. It is highly likely that the devices tested during the present study were audible to Eurasian badgers. Moreover, the device was emitting at a SPL that should have caused great discomfort at 1 m, which corresponded to the approximate distance between devices and bait. Nevertheless, in the present study ultrasonic devices failed to significantly reduce bait consumption. Using a similar device, Mills et al. (2000) found little effect on domestic cat behaviour, despite their contention that the cats could hear the device (indicated by frequent ear-flicking) and concluded that the device did not compromise the cats’ welfare. Food limitation is known to reduce the efficacy of ultrasonic devices when they had previously controlled rat consumption of bait under unlimited food conditions (Shumake et al., 1982). The location for the present study sites was selected since it was known that badgers had access to other abundant food sources in the area. Consequently, baited plots almost certainly represented supplementary food rather than provision of an otherwise limited resource. Therefore, it is unlikely that food limitation influenced badgers’ responses to baited plots, which instead were considered to be responses to the treatments. In addition, since badgers chose to consume bait close to active ultrasonic devices despite the availability of alternative foods nearby, it is likely that impacts of the devices on badger welfare were minimal. Camera traps were used to monitor badger activity at baited plots during the current study. Despite the model used here proving the most reliable at capturing animal movements during
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trials of six different models (CSL, unpublished data), they probably did not capture every animal incursion into each plot. However, since all units were identical and camera settings were constant between units, there is no reason to suspect bias between units, and we conclude that they provided a reliable index of badger activity relative to each other. However, it was not possible to identify individual badgers or estimate local badger densities from photographs. This has implications for inferences regarding learned avoidance of treatments by badgers. It was not possible to produce evidence that individual badgers repeatedly visited plots, or that individuals visited more than one plot, nor was it possible to refute these. However, since 22% of photographs depicted multiple badgers foraging at plots at the same time, and 88% of plot.nights involved multiple visits to plots by badgers, it is likely that multiple badgers would have repeatedly visited multiple plots over the course of the experiment, and hence learned avoidance of treatments was distinctly possible. Moreover, since each group of four plots was established close to a main sett, it is likely that active badger territoriality limited the maximum number of badgers visiting any plot to the number of badgers within that social group. Social groups neighbouring those studied here comprised 2.7 0.5 (mean S.E.) badgers per social group during 1978, rising to 8.8 0.9 badgers in 1993 (Rogers et al., 1997), and local population abundance appears to have subsequently reached a plateau (Delahay et al., 2005). Since multiple badgers may have been present and opened different bowls within a given plot at the same time, the unit of analysis for bait consumption (the bowl) was justified. Moreover, since badgers were photographed at different plots within the same site at the same time on 78 occasions, it is likely that different badgers frequently opened different bowls within a site on the same night. However, we cannot discount the possibility that, on some occasions, one badger opened numerous bowls per plot or per site. If a single badger had opened multiple bowls at a given plot and consumed bait from them, the use of the bowl as the analytical unit would have inflated the degrees of freedom, enhancing the type 1 error rate. At the worst extreme, this may have meant there were no significant differences between treatments and controls or between treatments and we would conclude that the treatments had no demonstrable effects on bait consumption or badger activity. However, as discussed above, we consider it likely that bait from bowls within plots and within sites was regularly consumed by multiple badgers. Experiments on repellence of granivorous birds have demonstrated the utility of using more obvious and immediate cues to facilitate chemical repellence to protect growing crops. Treatment of crops with chemical feeding repellents and brightly coloured dyes conferred protection to crops only treated with dyes, since birds learned to associate the chemical repellent with the dye (Greig-Smith, 1990). Similarly, we had anticipated that when used in combination with the water jet the ultrasonic device should have been at least as effective as the water jet alone. Furthermore, the purpose of the C–WU–U treatment was to investigate whether association of the water jet treatment with the ultrasonic treatment could promote medium-long term plot avoidance by badgers despite removal of the water jet treatment. No such effect was evident since the ultrasonic treatment and the combined ultrasonic and water jet treatment did not reduce bait consumption or badger activity at plots in comparison to controls. The higher probability of bait consumption, under the ultrasonic and combined treatments, raises the possibility that the ultrasonic device may have acted as a signal to badgers of the presence of bait. Indeed, it is possible that the devices were audible to badgers from distances up to 100 m, and unlikely to be capable of being repellent until within 1 m or so. Experimental trials of ultrasound on cats provide a further potential reason why it may have acted as an attractant to badgers in the present study. Mills et al. (2000) found that their device emitted at frequencies used by rats during communication, and thus hypothesised that it may have attracted cats. As badgers
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also predate rats (Garnett et al., 2002), we speculate that this remains a possible (though not highly plausible) explanation for the poor performance of the ultrasonic device during the present study. This could also help explain why although the water jet significantly reduced bait consumption, this effect was negated when it was used in combination with the ultrasonic device. For both bait consumption and overall activity at both sites and whether treatments were analysed directly or as a combination of treatments, the results were consistent and we conclude that the ultrasonic treatment, at best had little or no significant effect on bait consumption, and at worst increased badger activity at baited plots. In contrast, the water jet treatment significantly reduced bait consumption. However, there was no significant difference in badger activity between the water jet and control plots, and the difference between fitted means of the probability of bait consumption, of the water jet treatment and the control was small (a difference of approximately 12%, Fig. 1). This suggests that, to badgers at these study sites, the benefit provided by bait tended to outweigh the cost of the water jet. These results are consistent with those of Tolhurst et al. (in press) who observed that badgers continually tested aversive barriers (electric fences) to rich food resources and re-gained access once the barriers had been removed. Our results suggest that badgers found the water jet treatment only mildly aversive and that the ultrasonic devices may have exacerbated badger activity. We found no evidence to suggest that the water jet device reinforced potential aversive effects of the ultrasonic device. 5. Conclusion Expanding human and wildlife populations in the UK mean that conflicts between the two are likely to continue to increase for the foreseeable future. Neither ultrasonic nor water jet devices, as tested during the current study, appear to offer sufficient benefits to justify their use as nonlethal approaches to badger damage control, and development of other methods is urgently required. These may include non-intrusive physical barriers or methods of population control that do not compromise the welfare of resident badgers. Acknowledgements This work was funded by Defra under contract WM0304. We are grateful to Mark Claridge, Tim Glover and Phil Court for field assistance, Jason Finney for data management, Dean Waters for measuring the outputs of ultrasonic devices and Louise Ward and two anonymous referees for helpful comments on an earlier draft of the manuscript. References Baker, S.E., Ellwood, S.A., Watkins, R.W., Macdonald, D.W., 2005a. A dose-response trial with ziram-treated maize and free-ranging European badgers Meles meles. Appl. Anim. Behav. Sci. 93, 309–321. Baker, S.E., Ellwood, S.A., Watkins, R.W., Macdonald, D.W., 2005b. Non-lethal control of wildlife: using chemical repellents as feeding deterrents for the European badger Meles meles. J. Appl. Ecol. 42, 921–931. Balestrieri, A., Remonti, L., 2000. Reduction of badger (Meles meles) setts damage to artificial elements of the territory. Hystrix 11, 95–98. Bender, H., 2003. Deterrence of kangaroos from agricultural areas using ultrasonic frequencies: efficacy of a commercial device. Wildl. Soc. Bull. 31, 1037–1046. Bomford, M., O’Brien, P.H., 1990. Sonic deterrents in animal damage control: a review of device tests and effectiveness. Wildl. Soc. Bull. 18, 411–422.
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Central Science Laboratory, 2007. Development of a strategy for resolving urban badger damage problems. Defra, Bristol, Report WM0304. Delahay, R.J., Davison, J., Poole, D.W., Matthews, A.J., Wilson, C.J., Heydon, M.J., Roper, T.J., in press. Managing conflict between badgers (Meles meles) and humans: recent trends in licensed operations to resolve badger-related problems in England. Mamm. Rev. Delahay, R.J., Smith, G.C., Ward, A.I., Cheeseman, C.L., 2005. Options for the management of bovine tuberculosis from badgers (Meles meles) to cattle: evidence from a long-term study. Mamm. Study 30, S73–S81. Edgar, J.P., Appleby, R.G., Jones, D.N., 2007. Efficacy of an ultrasonic device as a deterrent to dingoes (Canis lupus dingo): a preliminary investigation. J. Ethol. 25, 209–213. Fay, R.R., 1988. Hearing in Vertebrates: A Psychophysics Databook. Hill-Fay Associates, IL, USA. Garnett, B.T., Delahay, R.J., Roper, T.J., 2002. Use of cattle farm resources by badgers (Meles meles) and risk of bovine tuberculosis (Mycobacterium bovis) transmission to cattle. Proc. R. Soc. Lond. 269B, 1487–1491. Greig-Smith, P.W., 1990. Foraging behaviour. In: Monaghan, P., Wood-Gush, D.G.M. (Eds.), Managing the Behaviour of Animals. Chapman and Hall, London, pp. 9–47. Harris, S., Jefferies, D., Cheeseman, C., Booty, C., 1994. Problems with Badgers? RSPCAWildlife Department, Horsham, UK. La Voie, G.K., Glahn, J.F., 1977. Ultrasound as a deterrent to Rattus norvegicus. J. Stored Prod. Res. 13, 23–28. Mathews, A.J., Wilson, C.J. 2005. The Management of Problems Involving Badgers; Protection of Badgers Act 1992 Licensing Cases 1997–1999. Report by the Rural Development Service, DEFRA, UK. Mills, D.S., Bailey, S.L., Thurstons, R.E., 2000. Evaluation of the welfare implications and efficacy of an ultrasonic ‘deterrent’ for cats. Vet. Rec. 147, 678–680. Nelson, S.H., Evans, A.D., Bradbury, R.B., 2006. The efficacy of an ultrasonic cat deterrent. Appl. Anim. Behav. Sci. 96, 83–91. Poole, D.W., McKillop, I.G., 1999. Comparison of the effectiveness of two types of electric fences to exclude badgers. Crop Prot. 18, 61–66. Rogers, L.M., Cheeseman, C.L., Mallinson, P.J., 1997. The demography of a high-density badger (Meles meles) population in the west of England. J. Zool. Lond. 242, 705–728. Shumake, S.A., Kolz, A.L., Crane, K.A., Johnson, R.E., 1982. Variables affecting ultrasound repellency in Philippine rats. J. Wildl. Manage. 46, 148–155. Tolhurst, B.A., Ward, A.I., Delahay, R.J., MacMaster, A.-M., Roper, T.J., in press. The behavioural responses of badgers (Meles meles) to exclusion from farm buildings using an electric fence. Appl. Anim. Behav. Sci., doi:10.1016/ j.applanim.2007.11.006. Ward, A.I., Tolhurst, B.A., Roper, T.J., Delahay, R.J., in press. A survey of badger access to farm buildings and facilities in relation to contact with cattle. Vet. Rec. Wilson, C.J., 1993. Badger damage to growing oats and an assessment of electric fencing as a means of its reduction. J. Zool. Lond. 231, 668–675. Wilson, C.J., Symes, R.G., 1998. The management of problems involving badgers; Protection of Badgers Act cases dealt with on behalf of the Ministry of Agriculture, Fisheries and Food from 1992 to 1996. Report by the Farming and Rural Conservation Agency, UK.
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Deterrent or dinner bell? Alteration of badger activity and feeding at baited plots using ultrasonic and water jet devices Alastair I. Ward *, Ste´phane Pietravalle, David P. Cowan, Richard J. Delahay Central Science Laboratory, Sand Hutton, York YO41 1LZ, UK Received 6 November 2007; received in revised form 28 May 2008; accepted 4 June 2008 Available online 16 July 2008
Abstract The increasing incidence of reports of damage caused by Eurasian badgers (Meles meles) in UK urban environments requires the development of effective, humane, non-lethal solutions. Ultrasonic deterrents are widely available to the public and are sold as a humane solution to the presence of unwanted animals in urban gardens. The reported failure of some ultrasonic devices may be caused by habituation of target animals to the devices and the lack of association with a negative, physical stimulus. We tested the ability of a commercially available, motion sensor-triggered ultrasonic device and a motion sensor-triggered water jet device, alone and in combination, to alter badger activity and feeding at baited plots. The ultrasonic device, whether used alone or in combination with the water jet, was associated with significantly higher badger activity at baited plots in comparison to control plots, and bait consumption was higher when the ultrasonic device was used alone. When the water jet was used alone, bait consumption was significantly reduced in comparison to control plots, but badger activity was not. There was no evidence to suggest that aversion to the ultrasonic device could be reinforced by the water jet, but some evidence to suggest that ultrasonic devices may have attracted badgers to baited plots. While the effects of the water jet on bait consumption were statistically significant, they were also very small (a 12% difference between the treatment and control fitted means). We conclude that neither device, used alone or in combination, present effective solutions to the growing problem of urban badger damage. Crown Copyright # 2008 Published by Elsevier B.V. All rights reserved. Keywords: Eurasian badger; Area repellent; Ultrasound deterrent; Urban garden; Water jet deterrent
* Corresponding author. Tel.: +44 1904 462077; fax: +44 1904 462111. E-mail address: [email protected] (A.I. Ward). 0168-1591/$ – see front matter. Crown Copyright # 2008 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.applanim.2008.06.004
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1. Introduction Increasing interest in non-lethal approaches to resolving human–wildlife conflicts requires the development and evaluation of novel techniques. Cases of physical damage to property and infrastructure caused by Eurasian badgers (Meles meles) are relatively common within the UK (Wilson and Symes, 1998; Mathews and Wilson, 2005; Delahay et al., in press) and have been recorded elsewhere in Europe (Balestrieri and Remonti, 2000). Reports of badger-related problems in urban areas of the UK have increased in recent years (Delahay et al., in press). These problems typically comprise either the undermining of property (i.e. buildings and other structures) during badger sett (underground burrow) construction, or digging damage to gardens. These problems are currently dealt with using non-lethal methods such as the exclusion of badgers from the problem sett (Harris et al., 1994; Mathews and Wilson, 2005; Central Science Laboratory, 2007). The badger is a protected species in the UK, thus any action requiring interference with badgers themselves, or their setts requires a licence from the appropriate statutory Government agency under the Protection of Badgers Act 1992. However, sett exclusions can be problematic, and suffer a high failure rate, particularly when the aim is the closure of a main sett in an urban area (Delahay et al., in press). Development of an effective area deterrent could provide a useful tool to aid exclusions and to deter badger activity in areas susceptible to damage. Chemical feeding deterrents have been used against badgers with some success (Baker et al., 2005a,b) but these only prevent consumption of food that animals have been conditioned against, and do not repel them from the area containing the food. Electric fencing has also been used successfully to exclude badgers from crop fields (Wilson, 1993; Poole and McKillop, 1999) and farm buildings (Tolhurst et al., in press), but in urban gardens, health and safety considerations and maintenance requirements limit its applicability. Ultrasonic deterrents are widely available to the public as a putatively humane, cost-effective and easy alternative to lethal control of wild animals (Bomford and O’Brien, 1990). However, studies of the effectiveness of such devices report ambiguous results. Nelson et al. (2006) observed a decrease in the frequency and duration of visits by domestic cats to urban gardens when motion sensor-triggered ultrasonic deterrents were actively emitting a signal of 21–23 kHz at 96 db at 1 m. Shumake et al. (1982) found that three ultrasonic devices emitting constantly at 20, 40 and 20–30 kHz at 118, 116 and 103 db at 30 cm, respectively, all deterred Philippine rats (Rattus rattus mindanensis) from feeding at baited points. Conversely, Mills et al. (2000) could not repel domestic cats from an area using an ultrasonic device emitting a signal of 19– 30 kHz at 100 db at 1 m. In addition, Bender (2003) did not observe altered behaviour or reduced site occupancy among eastern grey and red kangaroos (Macropus giganteus and M. rufus, respectively) in response to two ultrasonic devices emitting signals of 17–27 kHz at 70 and 35 db at 50 m. Edgar et al. (2007) reported a similar failure to inhibit dingo (Canis lupus dingo) activity at baited plots using an ultrasonic device emitting at 24–25 kHz at 82 db (measured directly in front of the device). Bomford and O’Brien (1990) concluded that, at best, ultrasonic deterrents might provide short-term, transient benefits. Nevertheless, such devices continue to be sold by a large number of suppliers, although claims of their efficacy have yet to be tested for a wide range of species. Indeed, until recently, the efficacy of ultrasonic deterrents had not been reported against any wild canids (Edgar et al., 2007). Although there appears to be no published information on their effectiveness against wild mustelids, these devices have been employed by the public in the UK with the intention of deterring badgers from their property.
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Failure of some ultrasonic devices to promote area deterrence is likely to be largely due to four factors. Firstly, if animals are highly motivated, such as by extreme hunger, it is unlikely that ultrasound will deter them from feeding (Shumake et al., 1982). Secondly, the ultrasound signal may be out with the hearing range of the target species. Thirdly, devices may emit with insufficient sound pressure (130 db is generally regarded as sufficient to cause discomfort and/or pain), in which case, the device may act as a signal, but not a repellent. Finally, habituation of animals to emitted ultrasound may reduce the efficacy of such devices over time (La Voie and Glahn, 1977; Shumake et al., 1982). When the device acts as a signal, or when animals have become habituated to it, encouraging them to associate the ultrasound with an aversive stimulus may enhance its effectiveness. However, behavioural reinforcement of ultrasound with an aversive stimulus has yet to be reported to our knowledge. We aimed to test the efficacy of a commercially available ultrasonic deterrent, both alone and reinforced with a commercially available water jet device, in terms of its ability to alter badger activity and bait consumption at baited plots. 2. Methods A replicated experiment was undertaken to determine whether a motion sensor-triggered ultrasonic device and a motion sensor-triggered water jet device, alone and in combination, could deter badgers from feeding on peanuts at bait stations. Both items were commercially available products, marketed to keep unwanted cats and other animals out of gardens. The manufacturer claimed that the ultrasonic device could protect areas up to 5.5 m2. Water jet devices were intended to be connected to a mains water supply. However, due to this experiment being undertaken in a rural area where no mains water was available, water jet devices were coupled using plastic hose pipes to 50 l plastic water tanks raised above the device either by placing the tank uphill of it or by raising the tank on a scaffold platform. This allowed water to flow under the force of gravity and produced sufficient pressure to eject a jet of water horizontally at a maximum height of 50 cm, with a total volume of 400–450 ml, 5–10 m from the device when activated. The jet of water was sprayed for 4 s over an arc set to 908 so that bait stations would be covered in water when activated. Ultrasonic devices were powered by one 9v PP3 cell each. The sound pressure level (SPL) of the ultrasonic device was measured in an anechoic chamber at 1 m distance using a 1/4 in. air dilatory microphone attached to an oscilloscope via a preamplifier. Measurements from the oscilloscope (in volts) were converted into SPL (in decibels) by calibration against a calibration device emitting at a known SPL. The frequency and energy of ultrasound emissions was measured at approximately 5 m distance using a Pettersson D1000X time expansion ultrasound detector (Pettersson Elektronic, Uppsala, Sweden). Three sites close to Woodchester Park on the Cotswold escarpment of Gloucestershire, UK were chosen on the basis that each was close to an active main badger sett where badgers had prior experience of foraging on peanuts. Badgers at these sites were known to visit farm buildings to forage on stored feed (Garnett et al., 2002; Ward et al., in press). At each site, four plots were established equidistant to the sett and with 100 m between them. At each plot four plastic bowls were buried flush with the ground, in a square pattern and each bowl was covered with a stone paving slab weighing approximately 4 kg, to prevent species other than badgers from accessing the bait. All bowls were filled with 150 ml of peanuts. Each plot was surrounded with 8 m of single strand electric fencing (to prevent interference by cattle but allowing free entry and exit to badgers) and also contained a water jet device, an ultrasonic device and a motion sensor-triggered digital trail camera (DS-04IR, Penn’s Woods Products Inc., Pennsylvania, USA) to monitor activity. These had previously been independently assessed as the most suitable model for indexing animal activity, from six different models of trail camera (Central Science Laboratory, unpublished data). Trail cameras were set to take photographs under infrared illumination, and record the time and date on each photograph, between dusk and dawn at 1-min intervals when motion was detected within the plot. It was not possible to determine the number of badgers visiting each plot, or to identify individual badgers from photographs. Instead, the number of badger photographs per plot per night was taken as an index of badger activity.
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The experiment was organised into three phases. During phase 1 plots were baited and monitored with no treatments allocated, in order to allow badgers to become familiar with feeding at baited plots. The phase was ended when bait consumption was observed at every plot for three consecutive nights. During phase 2 treatments were randomly allocated to each plot per site and monitoring undertaken as before, but for 14 nights. During phase 3, treatments were purposively switched between sites and monitoring undertaken as before. The treatments were (a) ultrasonic device active, (b) water jet device active, (c) both ultrasonic and water jet devices active (combined treatment) and (d) control (no equipment active) (Table 1). Treatments were not randomly switched between phases 2 and 3 because of data considerations and in order to address specific questions. The water jet treatment was removed from the experiment at the end of phase 2 because differences between it and the other treatments were already apparent. In contrast, potential effects of the ultrasonic treatment were not apparent at the end of phase 2, and so replication of this treatment was enhanced by replacing the water jet treatment with the ultrasonic treatment, as well as maintaining it at the same plots as during phase 2, to investigate longer-term effects. This yielded twice as many plots under the ultrasonic treatment during phase 3 than during phase 2. Finally, whether badgers could be conditioned against the ultrasonic treatment, during phase 3, by combining it with the water jet treatment during phase 2, was considered of applied significance. Conversely, we considered it unlikely that badgers would be conditioned against the water jet by the ultrasonic within the combined treatment during phase 2, hence did not consider it worthwhile to follow the combined treatment in phase 2 with the water jet treatment alone in phase 3. Phase 3 was ended when it became apparent that no further treatment effects were likely to be observed (i.e. little or no variation in bait consumption). Monitoring consisted of recording how many bowls had been disturbed and measuring the volume of peanuts left per bowl and per plot each morning. In addition, the number of photographs taken of badgers by the trail cameras, were used to describe the relative frequency of visits to plots (a measure of activity). Bowls were replenished with peanuts to maintain bait volumes at 150 ml on each day of the experiment. Paving slabs were then replaced over the bowls and gaps resulting from badger digging were in-filled with earth to prevent access by other wildlife. 2.1. Statistical analysis Data were analysed using GenStat 9 (VSN International, Hemel Hempstead, UK). Initially, response variables were the volume and proportion of bait consumed per bowl, and the number of badger photographs taken by trail cameras per night per plot. Treatments were analysed as two sets of explanatory variables: ‘direct treatments’ and ‘combination of treatments’. ‘Direct treatments’ assumed independence of treatment effects between phases, irrespective of the treatment that had been applied at each plot during the previous phase, and was intended to identify gross treatment effects. For the ‘combination of treatments’ analysis no such assumption was made, instead this approach tested whether treatment effects were dependent on the sequence in which they were applied. Treatment combinations were analysed as discrete units. Hence, there were four different treatments: C–U–U, C–W–C, C–WU–U, C–C–WU, where C = control, U = ultrasonic Table 1 Experimental design to test the effectiveness of an ultrasonic device and a water jet device at preventing badgers feeding at baited plots Plot
1 2 3 4
Site 1
Site 2
Site 3
Phase 2
Phase 3
Phase 2
Phase 3
Phase 2
Phase 3
U W WU C
U C U WU
U C WU W
U WU U C
U WU W C
U U C WU
U = ultrasonic, W = water jet, WU = ultrasonic and water jet, C = control (i.e. no treatment).
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device active, W = water jet device active, and WU = water jet and ultrasonic devices active, and where the first letter refers to the treatment applied during phase 1, the second letter(s) to phase 2 and the third to phase 3. Potential differences between sites were accounted for as a random term in all analyses. For bait consumption a generalised linear mixed model was used with a logit transform to account for the binary nature of the data (see below). The number of badger photographs per plot per night was analysed using a simpler restricted maximum likelihood model since there was no evidence of data departure from normality. The position of bowls and plots remained constant throughout the experiment. However, since different badgers may have consumed bait at a given plot between nights, and in consideration of the limited variability in response data between treatments, data from the same plots and bowls were not treated as repeated measures during analysis. Data were analysed from all phases, and, under separate analyses, data from phase 1 were excluded in order to avoid potential effects on control data of badger naivety to bait stations. During all analyses statistical significance was inferred at the 5% level.
3. Results Ultrasonic devices were emitting frequencies from approximately 15–30 kHz, with strong emissions cycling in the range 23–25 kHz. Peak energy was recorded at 23 kHz. The SPL of emissions was 138 db at 10 cm and 118 db at 1 m. Assuming equivalence to sound audible to humans, this would correspond to an SPL of 78 db at 100 m, however, atmospheric attenuation would considerably reduce this. Ultrasound was emitted for 5 s from detection of movement with a 30 s delay until the device could activate again. Bowls containing bait were uncovered, the contents consumed and photographs taken by trail cameras during all experimental phases at two of the three sites. At the third site, despite close proximity to an active sett, no badger activity was recorded at baited plots and the site was excluded from further analysis. At the two active sites, across all phases, bowls were uncovered on 793 of 864 bowl.nights. All the bait had disappeared (presumed eaten by badgers) in all but 11 instances where bowls had been uncovered by badgers, and on four such occasions no bait was consumed. Consequently, and since other species may have consumed left-over bait once bowls were uncovered by badgers (see below), we analysed bait consumption as a binary response: some bait consumed/no bait consumed. Of 2063 photographs, 1626 were taken of badgers, 52 of domestic cattle (at the edge and outside of plots), 24 of foxes (Vulpes vulpes), 11 of rabbits (Oryctolagus cuniculus), 12 of roe deer (Capreolus capreolus, at the edge and outside of plots), two of pheasants (Phasianus colchicus), one of a crow (Corvus corone) and one of a kestrel (Falco tinnunculus) at bait plots. A further 334 photographs either contained images of people or vehicles travelling close to the plots, or the agent triggering the cameras was not apparent. Some of the animals photographed, other than badgers, may have consumed bait from plots uncovered by badgers. However, it was considered highly unlikely that any species of wildlife other than badgers would have moved the paving slabs, and also that badgers would generally have consumed at least some bait after opening a bowl. Consequently, photographs of animals other than badgers were excluded from analysis, but data were retained from plots on nights during which other species were photographed. Among photographs of badgers, 1264 were of single animals, 279 of a pair, 68 of three animals, 11 of four animals, and four of five animals. The number of badger photographs at a plot on a given night varied from 0 to 107. From 166 plot.nights when photographs were taken, only a single photograph was taken on 24 plot.nights, on 53 plot.nights between two and ten photographs were taken, on 75 plot.nights between 11 and 50 photographs were taken and on 14
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Table 2 Effects of the sequence of treatments on the relative frequency of bait consumption at baited plots Treatment
Phase
% nights where bait was consumed
C–W–C
1 2 3
49 76 100
C–U–U
1 2 3
78 100 100
C–WU–U
1 2 3
85 100 98
C–C–WU
1 2 3
70 100 91
Data are pooled across sites.
plot.nights more than 50 photographs were taken. Photographs were taken at different plots within the same site, at the same time, on the same date on 78 occasions. On 129 occasions photographs at the same site and on the same date were taken at different plots within 1 min of each other. There was some evidence that badgers became habituated to feeding at plots with time. At all plots, including controls, bait was consumed more frequently during phases 2 and 3 than during phase 1 (Table 2). Moreover, during phase 1, the number of nights since the start of monitoring was significantly associated with the likelihood of a plot being uncovered by badgers (logistic regression, Wald = 19.226, d.f. = 1, P < 0.001). During nights 3, 4 and 5 of phase 1, bait was consumed at every plot, and so the phase was ended. Bait consumption at plots varied very little during phase 3 (Table 2), which was ended after eight nights. Irrespective of whether data were analysed directly, as a sequence of treatments or including or excluding phase 1 data, no site effect was evident but the treatment effect was significant (Table 3). When analysed directly and including phase 1 data, the water jet treatment was associated with a significantly lower probability of bait consumption than all other treatments, Table 3 Effects of treatments and sites on the likelihood of bait consumption and activity at baited plots Treatments analysed
Explanatory variable
Phases included
Site effect Variance component
Directly
As combinations
Treatment effect S.E.
Wald
d.f.
P
Bait consumption
1, 2, 3 2, 3
0.06 0.02
0.13 0.12
28.57 38.76
3 3
<0.001 <0.001
Activity
1, 2, 3 2, 3
1.44 8.49
3.14 13.41
18.93 9.85
3 3
<0.001 0.020
Bait consumption
1, 2, 3 2, 3
0.05 0.01
0.12 0.09
27.66 20.20
3 3
<0.001 <0.001
Activity
1, 2, 3 2, 3
1.44 8.52
3.14 13.41
17.30 15.66
3 3
<0.001 <0.001
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Fig. 1. Back-transformed fitted means and 95% confidence intervals for the probability of bait being consumed under each of three treatments and a control. Data are from all three phases.
including the control. In contrast, the ultrasonic treatment was associated with a significantly higher probability of bait consumption than controls, but the combined treatment did not differ significantly from controls (Fig. 1). Under these same conditions badger activity was significantly higher under the combined treatment and the ultrasonic treatment (which did not differ significantly from each other) than the water jet treatment and the control (Fig. 2). Analysed directly, and excluding phase 1 data, the water jet treatment was still associated with a significantly lower probability of bait consumption than the ultrasonic or combined treatments. However, all bait was consumed from all control plots during phases 2 and 3, so no statistical comparisons were possible between treatments and controls due to invariability in data from control plots. With phase 1 data excluded, the combined treatment was associated with significantly higher badger activity than the controls, but the water jet and ultrasonic treatments were not significantly different from controls. Activity under the water jet treatment was significantly lower than the ultrasonic and combined treatment. Differences under the water jet treatment were significant in spite of 36% fewer observations than the combined treatment, due the water jet treatment not being repeated during phase 3. When analysed as serial combinations of treatments and including phase 1 data, C–W–C was associated with a significantly lower probability of bait consumption and badger activity than all other treatment combinations, which were not significantly different from each other (Figs. 3 and 4). Excluding phase 1 data badger activity was still significantly lower under the C–W–C treatment than all other treatment combinations and the probability of bait consumption was significantly lower than the C–WU–U and C–C–WU treatments, but the lack of variation in bait consumption under the C–U–U treatment precluded statistical comparison. Nevertheless, this lack of variation was due to all bait being consumed under this treatment sequence during phases 2 and 3.
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Fig. 2. Fitted means and 95% confidence intervals for the number of photographs of badgers taken per night under each of the three treatments and controls. Data are from all three phases. The error bar to the extreme left of the graph is the least significant difference (at P = 0.05).
Fig. 3. Back-transformed fitted means and 95% confidence intervals for the probability of bait being consumed under each of the four treatment combinations. Data are from all three phases.
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Fig. 4. Fitted means and 95% confidence intervals for the number of photographs of badgers taken per night under each of the four treatment combinations. Data are from all three phases. The error bar to the extreme left of the graph is the least significant difference (at P = 0.05).
4. Discussion Emission frequency and intensity are important factors determining the likely efficacy of ultrasonic devices (Shumake et al., 1982). Fay (1988) reported that domestic dogs can hear in the range of 67–45,000 Hz, racoons (Procyon lotor) from 100 to 40,000 Hz and domestic ferrets (Mustela putorius furo) from 160 to 44,000 Hz. It is highly likely that the devices tested during the present study were audible to Eurasian badgers. Moreover, the device was emitting at a SPL that should have caused great discomfort at 1 m, which corresponded to the approximate distance between devices and bait. Nevertheless, in the present study ultrasonic devices failed to significantly reduce bait consumption. Using a similar device, Mills et al. (2000) found little effect on domestic cat behaviour, despite their contention that the cats could hear the device (indicated by frequent ear-flicking) and concluded that the device did not compromise the cats’ welfare. Food limitation is known to reduce the efficacy of ultrasonic devices when they had previously controlled rat consumption of bait under unlimited food conditions (Shumake et al., 1982). The location for the present study sites was selected since it was known that badgers had access to other abundant food sources in the area. Consequently, baited plots almost certainly represented supplementary food rather than provision of an otherwise limited resource. Therefore, it is unlikely that food limitation influenced badgers’ responses to baited plots, which instead were considered to be responses to the treatments. In addition, since badgers chose to consume bait close to active ultrasonic devices despite the availability of alternative foods nearby, it is likely that impacts of the devices on badger welfare were minimal. Camera traps were used to monitor badger activity at baited plots during the current study. Despite the model used here proving the most reliable at capturing animal movements during
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trials of six different models (CSL, unpublished data), they probably did not capture every animal incursion into each plot. However, since all units were identical and camera settings were constant between units, there is no reason to suspect bias between units, and we conclude that they provided a reliable index of badger activity relative to each other. However, it was not possible to identify individual badgers or estimate local badger densities from photographs. This has implications for inferences regarding learned avoidance of treatments by badgers. It was not possible to produce evidence that individual badgers repeatedly visited plots, or that individuals visited more than one plot, nor was it possible to refute these. However, since 22% of photographs depicted multiple badgers foraging at plots at the same time, and 88% of plot.nights involved multiple visits to plots by badgers, it is likely that multiple badgers would have repeatedly visited multiple plots over the course of the experiment, and hence learned avoidance of treatments was distinctly possible. Moreover, since each group of four plots was established close to a main sett, it is likely that active badger territoriality limited the maximum number of badgers visiting any plot to the number of badgers within that social group. Social groups neighbouring those studied here comprised 2.7 0.5 (mean S.E.) badgers per social group during 1978, rising to 8.8 0.9 badgers in 1993 (Rogers et al., 1997), and local population abundance appears to have subsequently reached a plateau (Delahay et al., 2005). Since multiple badgers may have been present and opened different bowls within a given plot at the same time, the unit of analysis for bait consumption (the bowl) was justified. Moreover, since badgers were photographed at different plots within the same site at the same time on 78 occasions, it is likely that different badgers frequently opened different bowls within a site on the same night. However, we cannot discount the possibility that, on some occasions, one badger opened numerous bowls per plot or per site. If a single badger had opened multiple bowls at a given plot and consumed bait from them, the use of the bowl as the analytical unit would have inflated the degrees of freedom, enhancing the type 1 error rate. At the worst extreme, this may have meant there were no significant differences between treatments and controls or between treatments and we would conclude that the treatments had no demonstrable effects on bait consumption or badger activity. However, as discussed above, we consider it likely that bait from bowls within plots and within sites was regularly consumed by multiple badgers. Experiments on repellence of granivorous birds have demonstrated the utility of using more obvious and immediate cues to facilitate chemical repellence to protect growing crops. Treatment of crops with chemical feeding repellents and brightly coloured dyes conferred protection to crops only treated with dyes, since birds learned to associate the chemical repellent with the dye (Greig-Smith, 1990). Similarly, we had anticipated that when used in combination with the water jet the ultrasonic device should have been at least as effective as the water jet alone. Furthermore, the purpose of the C–WU–U treatment was to investigate whether association of the water jet treatment with the ultrasonic treatment could promote medium-long term plot avoidance by badgers despite removal of the water jet treatment. No such effect was evident since the ultrasonic treatment and the combined ultrasonic and water jet treatment did not reduce bait consumption or badger activity at plots in comparison to controls. The higher probability of bait consumption, under the ultrasonic and combined treatments, raises the possibility that the ultrasonic device may have acted as a signal to badgers of the presence of bait. Indeed, it is possible that the devices were audible to badgers from distances up to 100 m, and unlikely to be capable of being repellent until within 1 m or so. Experimental trials of ultrasound on cats provide a further potential reason why it may have acted as an attractant to badgers in the present study. Mills et al. (2000) found that their device emitted at frequencies used by rats during communication, and thus hypothesised that it may have attracted cats. As badgers
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also predate rats (Garnett et al., 2002), we speculate that this remains a possible (though not highly plausible) explanation for the poor performance of the ultrasonic device during the present study. This could also help explain why although the water jet significantly reduced bait consumption, this effect was negated when it was used in combination with the ultrasonic device. For both bait consumption and overall activity at both sites and whether treatments were analysed directly or as a combination of treatments, the results were consistent and we conclude that the ultrasonic treatment, at best had little or no significant effect on bait consumption, and at worst increased badger activity at baited plots. In contrast, the water jet treatment significantly reduced bait consumption. However, there was no significant difference in badger activity between the water jet and control plots, and the difference between fitted means of the probability of bait consumption, of the water jet treatment and the control was small (a difference of approximately 12%, Fig. 1). This suggests that, to badgers at these study sites, the benefit provided by bait tended to outweigh the cost of the water jet. These results are consistent with those of Tolhurst et al. (in press) who observed that badgers continually tested aversive barriers (electric fences) to rich food resources and re-gained access once the barriers had been removed. Our results suggest that badgers found the water jet treatment only mildly aversive and that the ultrasonic devices may have exacerbated badger activity. We found no evidence to suggest that the water jet device reinforced potential aversive effects of the ultrasonic device. 5. Conclusion Expanding human and wildlife populations in the UK mean that conflicts between the two are likely to continue to increase for the foreseeable future. Neither ultrasonic nor water jet devices, as tested during the current study, appear to offer sufficient benefits to justify their use as nonlethal approaches to badger damage control, and development of other methods is urgently required. These may include non-intrusive physical barriers or methods of population control that do not compromise the welfare of resident badgers. Acknowledgements This work was funded by Defra under contract WM0304. We are grateful to Mark Claridge, Tim Glover and Phil Court for field assistance, Jason Finney for data management, Dean Waters for measuring the outputs of ultrasonic devices and Louise Ward and two anonymous referees for helpful comments on an earlier draft of the manuscript. References Baker, S.E., Ellwood, S.A., Watkins, R.W., Macdonald, D.W., 2005a. A dose-response trial with ziram-treated maize and free-ranging European badgers Meles meles. Appl. Anim. Behav. Sci. 93, 309–321. Baker, S.E., Ellwood, S.A., Watkins, R.W., Macdonald, D.W., 2005b. Non-lethal control of wildlife: using chemical repellents as feeding deterrents for the European badger Meles meles. J. Appl. Ecol. 42, 921–931. Balestrieri, A., Remonti, L., 2000. Reduction of badger (Meles meles) setts damage to artificial elements of the territory. Hystrix 11, 95–98. Bender, H., 2003. Deterrence of kangaroos from agricultural areas using ultrasonic frequencies: efficacy of a commercial device. Wildl. Soc. Bull. 31, 1037–1046. Bomford, M., O’Brien, P.H., 1990. Sonic deterrents in animal damage control: a review of device tests and effectiveness. Wildl. Soc. Bull. 18, 411–422.
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