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Use of cattle troughs by badgers (Meles meles)
Applied Animal Behaviour Science 80 (2003) 1–8
Use of cattle troughs by badgers (Meles meles) A potential route for the transmission of bovine tuberculosis (Mycobacterium bovis) to cattle B.T. Garnetta,b,*, T.J. Ropera, R.J. Delahayb a
School of Biological Sciences, University of Sussex, Brighton BN1 9QG, UK b Central Science Laboratory, Sand Hutton, York YO41 1LZ, UK Accepted 7 August 2002
Abstract Cattle feedtroughs that are contaminated with badger excreta constitute a potential transmission route for the spread of bovine tuberculosis (Mycobacterium bovis) from badgers (Meles meles) to cattle. In order to investigate the maximum height to which a trough would have to be raised to make it secure against badgers, we presented wild badgers with an experimental trough that could be set to a range of heights. In two separate experiments, a total of at least 12 badgers from two social groups at Woodchester Park, Gloucestershire, South-West England managed to climb into the trough when it was set at heights above 80 cm (i.e. higher than the current recommended safety guidelines for farmers). The maximum height to which badgers could climb was 115 cm, which would place the trough beyond the reach of calves, young heifers and bullocks. We conclude that there is no safe height at which troughs can be set to feed young cattle while excluding badgers. Exclusion of badgers from cattle troughs therefore requires the development of new trough designs. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Badgers; Cattle; Cattle troughs; Bovine tuberculosis; Foraging
1. Introduction The incidence of bovine tuberculosis (Mycobacterium bovis: referred to below as bTB) in UK cattle herds has increased from 0.05% in the late 1970s to 2.7% in 2000 (MAFF,
* Corresponding author. Present address: CSL Research Unit, Woodchester Park, Nympsfield, Gloucs GL10 3UJ, UK. Tel.: þ44-1453-860-777. E-mail address: [email protected] (B.T. Garnett).
0168-1591/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 1 5 9 1 ( 0 2 ) 0 0 2 0 4 - 6
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B.T. Garnett et al. / Applied Animal Behaviour Science 80 (2003) 1–8
2001). This has serious economic implications both for the farming industry and the public finances, and raises significant animal welfare concerns (Krebs et al., 1997). The Eurasian badger (Meles meles) is susceptible to bTB infection and is suspected of transmitting the disease to cattle in the UK and Ireland (Krebs et al., 1997). However, despite strong circumstantial evidence of a link between bTB in cattle and badgers, little is known about how the disease is transmitted. Research to date has concentrated on the risks to cattle from pasture contaminated with badger excreta (e.g. Brown, 1993; Hutchings and Harris, 1997, 1999) but other evidence suggests that cattle are averse to grazing near badger faeces and urine (Benham and Broom, 1991), unless forced to do so by high grazing pressure (Hutchings and Harris, 1997). In addition, M. bovis bacilli have a short lifespan on pasture, surviving for up to three and fourteen days on summer pastures, in urine and faeces, respectively (MAFF, 1979; Jackson et al., 1995). Cheeseman and Mallinson (1981) have proposed an alternative potential transmission route, involving the contamination of farm buildings with badger excretory products. This hypothesis initially stemmed from observations of two tuberculous badgers feeding and sheltering in buildings on cattle farms. Subsequently, during a recent radio-tracking study at Woodchester Park, Gloucestershire, South-West England (Garnett et al., 2002), at least 26 individual badgers from two social groups were observed entering farm buildings and feeding from cattle troughs. The badgers in question, which included three individuals known to be infected with bTB, climbed into feed troughs at heights of up to 70.5 cm (Garnett et al., in press). Accumulations of badger droppings were found in these feed troughs and further contamination may have occurred from urine, sputum, and draining abscesses. Whilst feeding from the troughs, badgers also occasionally came into close proximity to feeding cattle, raising the possibility of direct aerosol transmission of M. bovis. Other studies have also reported the use of cattle feed and water troughs by badgers (Muirhead et al., 1974; Sleeman and Mulcahy, 1993). In the UK, current government advice to farmers is that cattle troughs should be set above 80 cm in order to exclude badgers (MAFF, 1999a,b). However, no research has been conducted to investigate the climbing ability of badgers or to determine whether a height of 80 cm is a sufficient deterrent. The aim of the present study, therefore, was to determine the maximum height to which a cattle trough would need to be raised in order to make it inaccessible to badgers.
2. Materials and methods 2.1. Study site The study took place at Woodchester Park, Gloucestershire, in a 7 km2 study area consisting of a valley surrounded by farmland. The valley itself consisted of mixed woodland interspersed with short-grass pasture, while the surrounding farmland consisted mainly of pasture but also included some arable fields. The resident badger population consisted of 25 social groups that were the subject of an intensive capture-mark-recapture study (see Delahay et al., 2000).
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2.2. Capture and examination of badgers The study focused on two social groups (groups A and B) each containing 16 badgers. Badgers were captured in steel-mesh box-traps baited with peanuts, anaesthetised with ketamine hydrochloride at a dose rate of 20 mg kg1 (MacKintosh et al., 1976), weighed to the nearest 0.1 kg, and marked with a distinctive fur-clip on each flank, consisting of a combination of arrows, crosses, lines and squares (Stewart and MacDonald, 1997). Furclipping symbols were created by removing the dark outer guard hairs of the badger’s coat, leaving the pale under-fur exposed beneath. The resulting contrast between the two fur layers allowed visual identification at night when the badger’s coat was illuminated with infra-red light. Fur-clipping was not expected to compromise the animals’ thermoregulatory efficiency but, as a precaution, cubs were only fur-clipped after attaining 8 kg in weight. Samples of urine, faeces, sputum and pus from open bite wounds were taken from captured badgers for microbiological culture (Clifton-Hadley et al., 1993) and a blood sample was taken for the detection of antibodies to M. bovis using an ELISA test (Goodger et al., 1994). Positive culture and ELISA test results were taken as evidence of infection with, and exposure to, M. bovis, respectively (see Delahay et al., 2000). 2.3. Field trials A cattle feeding trough of standard half-drum design (184 cm long, 30 cm wide, 16 cm deep: Ritchie, Forfar, Scotland) was purchased for use in field trials. The legs of the trough were removed and replaced by four telescopic legs of 3.3-cm diameter steel tubing. These legs were smooth along their entire length to deny badgers any footholds. Each pair of legs was joined near the top by a horizontal bar, on which the trough itself rested (see Fig. 1). Data on badger visits to the trough were collected using a time-lapse video system and
Fig. 1. Female badger climbing into the experimental trough, which was set at a height of 85 cm.
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infra-red lighting. The camera was mounted on a tripod and placed 4.5 m from the trough, with a tripod-mounted infra-red light placed 2 m from the camera on either side. Continuous night-time footage was recorded on 4-h video tapes by setting the video recorder to 12-h time-lapse mode. 2.4. Procedure 2.4.1. Experiment 1 From 15th June to 15th September 2000 the trough and video surveillance equipment were positioned on level ground near to the main set of a badger social group (group A) that had had no prior access to cattle troughs. An area of soft mud and leaf litter was chosen to minimise any risk of injury to the badgers from falls. During routine trapping operations 11 badgers from this group were caught and fur-clipped. However, one of the marked animals disappeared shortly after the experiment began and was therefore excluded from subsequent analyses. Initially, the trough was left unbaited for 1 week to allow badgers to get used to its presence. It was then baited with peanuts for 3-day periods of filming, separated by periods varying from 1 to 14 days, when it was left unbaited in order to prevent the animals from becoming dependent on this unnatural source of food. Peanuts were used because they were a familiar food, having been used as bait for trapping. Initially, the height of the rim of the trough was set at 30 cm above ground level. The trough was then raised successively to heights of 45, 60, and 70 cm, respectively. It was only made available for one night at each of these heights since video recordings showed it to be readily accessible to most badgers. Thereafter, the trough was raised in further 5-cm increments, but the height was only increased when at least one individual had successfully climbed it. The experiment was terminated, and the highest accessible height judged to have been reached, when all badgers had refused to attempt climbing, or had attempted and failed to access the trough, on at least five occasions. 2.4.2. Experiment 2 Experiment 1 was designed to reveal the climbing potential of free-living badgers that lacked previous experience of cattle troughs. However, it could be argued that since the trough was first made available at a low height and was then progressively raised, these badgers had the opportunity to develop climbing skills during the course of the experiment. To control for this possibility, in Experiment 2 the baited trough was set at a height of 81 cm and placed at the main set of a second social group (group B). The height of 81 cm was chosen because official advice to farmers is that troughs raised to a height of over 80 cm should be inaccessible to badgers (MAFF, 1999a,b). The trough was left unbaited at the set for a week to allow the badgers to habituate to it, before baiting it and recording on videotape behaviour over a single night. 2.5. Behavioural classification and analysis A climbing attempt was deemed successful if a badger managed to gain a secure footing within the basin of the feeding trough. A failure was classified as any attempt during which
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the badger raised all four feet off the ground simultaneously but came back to ground without drawing its entire body into the trough basin, or lost its footing on all four feet and slipped onto its back or side. The influence of individual body weight on climbing ability was investigated using measurements taken during routine trapping operations in the 2 weeks prior to the experiment.
3. Results When the trough was set at a height of 30 cm, all 10 individually identifiable members of group A, plus at least four cubs, managed to climb into it on the first night. Thereafter, as the height of the trough was raised, the number of badgers successfully accessing it gradually declined until, at 80 cm, only two animals were successful (Fig. 2). Thereafter, there was a slight reversal of the downward trend, but at heights above 95 cm only one cub still managed to climb into the trough. This animal was finally deterred at a height of 120 cm. Badgers employed a range of techniques to feed from the trough. At a height of 30 cm, they could simply sit by the trough and eat. At 45 cm, they could reach the food by standing on their hind legs and resting their forepaws on the rim of the trough. At 60 cm, climbing was necessary for all but the largest males, and above 60 cm climbing was necessary for all badgers. Adults climbed the trough by standing or jumping and hooking their fore-claws over the trough rim or over one of the horizontal bars on which the trough rested, then swinging and hauling themselves up with their forelegs until their back legs could gain purchase on the trough rim (Fig. 1).
Fig. 2. Number of individually identifiable adult badgers, and minimum number of cubs, able successfully to access the experimental trough, as a function of trough height. Minimum number of cubs was recorded as the greatest number seen feeding simultaneously from the trough.
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Fig. 3. Relationship between the maximum height successfully climbed by individual badgers, and body weight.
From 110 to 115 cm, the single animal that was still successful managed to climb up the legs supporting the trough. It did this by opposing its fore- and hind-paws on the leg of the trough and then scaling upwards by moving each pair of paws alternately. With two to four such movements it could reach the trough rim or the horizontal bar on which the trough rested, and haul itself into the basin with its forelegs. The maximum height reached by individual badgers varied from 70 to 115 cm and was negatively correlated with body weight (Spearman test, rs ¼ 0:82, n ¼ 10, P < 0:01) (Fig. 3). One female that had tested positive for bTB managed to climb to a height of 95 cm, despite poor body condition and an inflamed lymph gland in her groin, which caused her to limp perceptibly. In Experiment 2, at least five badgers climbed into the trough on the first occasion that it was baited, at a height of 81 cm.
4. Discussion Recently published government guidelines for UK farmers recommend that cattle feed and water troughs be raised at least 80 cm off the ground in order to make them inaccessible to badgers (MAFF, 1999a,b). Our results, by contrast, show badgers climbing into and feeding from a trough that was set at heights of up to 115 cm. Since the trough was initially presented at a height of only 30 cm and was thereafter raised incrementally, it could be argued that the badgers were given the opportunity to improve their climbing skills, through learning, during the course of the experiment. However, in a second trial, in which the trough was presented to a different social group of badgers at a height of 81 cm, several animals succeeded in climbing into it on the first night that it was available. Thus, the climbing ability of badgers has been underestimated and troughs placed at a height of 80 cm are not safe, even from naive badgers.
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These results may have important implications for the spread of bTB to cattle. In a recent case study, badger droppings and urine, including droppings deposited by an animal known to be infected with bTB, were found in cattle troughs on a farm where a herd breakdown subsequently occurred (Garnett et al., 2002). In addition, when badgers eat cattle food they may contaminate it with saliva, pus from open lesions and other secretions, all of which can carry M. bovis bacilli (MAFF, 1979; Gallagher and Clifton-Hadley, 2000). The fact that badger body weight was negatively correlated with climbing success in our study might, paradoxically, mean that tuberculous badgers that are in poor body condition may be better at accessing troughs. Indeed, in the present study, an infected female that was in visibly poor condition managed to climb into the experimental trough at heights of up to 95 cm. Infected individuals may also be more motivated to feed from artificial resources such as cattle troughs and farm buildings (Cheeseman and Mallinson, 1981; Garnett et al., 2002). Badgers have been reported to climb stone walls, to access bird tables and to climb trees to heights of 5 m in order to raid bee and wasp nests (Neal and Cheeseman, 1996). Scaling of trees is done in a bear-like manner, whereby the animal grips the trunk with both forefeet, and both hind-feet, opposed to one another, and then shuffles upwards by moving each pair of feet alternately (Neal and Cheeseman, 1996). This technique was adapted to scale the smooth steel pole legs of the trough in the present study (of 3.3 cm diameter). Evidently the badger’s powerful limbs, plantigrade feet and long claws, which are primarily adapted for digging (Neal and Cheeseman, 1996), are also surprisingly effective for climbing. Making cattle troughs secure against badgers may require new designs of trough, rather than merely increasing the height to which troughs are raised off the ground. This is especially the case with troughs designed to feed calves, young heifers and bullocks, since raising such troughs sufficiently to deter badgers would make the food inaccessible to the livestock for which it is intended. Existing troughs could be modified by attaching a rolling bar to the trough rim, or a guard shield projecting from just below the trough. Alternatively some form of closed trough could be used, opening in response to a cow-collar transmitter or a pressure plate on the floor. These alternative trough designs are likely to deter badgers from climbing, but may require some further experimentation.
Acknowledgements This study forms part of a D.Phil. project by the first author, funded by the BBSRC. We thank the farmers and landowners in the Woodchester Park study area for their cooperation, the University of Sussex for the time-lapse camera and cattle trough, and Tony Hillman for electronics advice. We are also indebted to the field team at Woodchester Park for their expertise in trapping and handling badgers, and to the Veterinary Laboratories Agency and Audrey Harris for microbiological culture of clinical samples. All work involving badgers at Woodchester Park is carried out under Home Office licence and is subject to an internal ethical review process. We thank Chris Cheeseman, Lucy Rogers and Gavin Wilson for comments on an earlier draft.
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References Benham, P.F.J., Broom, D.M., 1991. Responses of dairy cows to badger urine and faeces on pasture with reference to bovine tuberculosis transmission. Br. Vet. J. 147, 517–531. Brown, J.A., 1993. Transmission of bovine tuberculosis (Mycobacterium bovis) from badgers (Meles meles) to cattle. Ph.D. thesis. University of Bristol, Bristol. Cheeseman, C.L., Mallinson, P.J., 1981. Behaviour of badgers (Meles meles) infected with bovine tuberculosis. J. Zool., Lond. 194, 284–289. Clifton-Hadley, R.S., Wilesmith, J.W., Stuart, F.A., 1993. Mycobacterium bovis in the European badger (Meles meles): epidemiological findings in tuberculous badgers from a naturally infected population. Epidemiol. Infect. 111, 9–19. Delahay, R.J., Langton, S., Smith, G.C., Clifton-Hadley, R.S., Cheeseman, C.L., 2000. The spatio-temporal distribution of Mycobacterium bovis (bovine tuberculosis) infection in a high-density badger population. J. Anim. Ecol. 69, 428–441. Gallagher, J., Clifton-Hadley, R.S., 2000. Tuberculosis in badgers a review of the disease and its significance for other animals. Res. Vet. Sci. 69, 203–217. Garnett, B.T., Delahay, R.J., Roper, T.J., in press. Use of farm buildings by badgers (Meles meles) and associated risks of Mycobacterium bovis transmission to cattle. In: Proceedings of the Third International Conference on Mycobacterium bovis. 13–16th August 2000, Cambridge. 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. B 269, 1487–1491. Goodger, J., Nolan, A., Russell, W.P., Dalley, D.J., Thorns, C.J., Stuart, F.A., Croston, P., Newell, D.G., 1994. Serodiagnosis of Mycobacterium bovis infection in badgers: development of an indirect ELISA using a 25 kDa antigen. Vet. Rec. 135, 82–85. Hutchings, M.R., Harris, S., 1997. Effects of farm management practices on cattle grazing behaviour and the potential for transmission of bovine tuberculosis from badgers to cattle. Vet. J. 153, 149–162. Hutchings, M.R., Harris, S., 1999. Quantifying the risks of TB infection to cattle posed by badger excreta. Epidemiol. Infect. 122, 167–174. Jackson, R., De Lisle, G.W., Morris, R.S., 1995. A study of the environmental survival of Mycobacterium bovis on a farm in New Zealand. New Zeal. Vet. J. 43, 346–352. Krebs, J.R., The Independent Scientific Review Group, 1997. Bovine Tuberculosis in Cattle and Badgers: Report to the Rt. Hon. Dr Jack Cunningham MP. MAFF Publications, London. MacKintosh, C.G., MacArthur, J.A., Little, T.W.A., Stuart, P., 1976. The immobilization of the badger (Meles meles). Br. Vet. Rec. 132, 609–614. MAFF, 1979. Third Report on Bovine Tuberculosis in Badgers. MAFF Publications, London. MAFF, 1999a. TB in Cattle: Reducing the Risk. MAFF Publications, London. MAFF, 1999b. Farm Biosecurity: Protecting Herd Health. MAFF Publications, London. MAFF, 2001. MAFF’s TB Webpages, http://www.maff.gov.uk/animalh/tb. Muirhead, R.A., Gallagher, J., Burns, K.S., 1974. Tuberculosis in wild badgers in Gloucestershire: epidemiology. Vet. Rec. 95, 552–555. Neal, E., Cheeseman, C.L., 1996. Badgers. T and A.D. Poyser, London. Sleeman, D.P., Mulcahy, M.F., 1993. Behaviour of Irish badgers in relation to bovine tuberculosis. In: Hayden, T.J. (Ed.), The Badger. Royal Irish Academy, Dublin, pp. 154–165. Stewart, P.D., MacDonald, D.W., 1997. Age, sex and condition as predictors of moult, and the efficacy of a novel fur-clip technique for individual marking of the European badger (Meles meles). J. Zool., Lond. 235, 237–245.
Use of cattle troughs by badgers (Meles meles) A potential route for the transmission of bovine tuberculosis (Mycobacterium bovis) to cattle B.T. Garnetta,b,*, T.J. Ropera, R.J. Delahayb a
School of Biological Sciences, University of Sussex, Brighton BN1 9QG, UK b Central Science Laboratory, Sand Hutton, York YO41 1LZ, UK Accepted 7 August 2002
Abstract Cattle feedtroughs that are contaminated with badger excreta constitute a potential transmission route for the spread of bovine tuberculosis (Mycobacterium bovis) from badgers (Meles meles) to cattle. In order to investigate the maximum height to which a trough would have to be raised to make it secure against badgers, we presented wild badgers with an experimental trough that could be set to a range of heights. In two separate experiments, a total of at least 12 badgers from two social groups at Woodchester Park, Gloucestershire, South-West England managed to climb into the trough when it was set at heights above 80 cm (i.e. higher than the current recommended safety guidelines for farmers). The maximum height to which badgers could climb was 115 cm, which would place the trough beyond the reach of calves, young heifers and bullocks. We conclude that there is no safe height at which troughs can be set to feed young cattle while excluding badgers. Exclusion of badgers from cattle troughs therefore requires the development of new trough designs. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Badgers; Cattle; Cattle troughs; Bovine tuberculosis; Foraging
1. Introduction The incidence of bovine tuberculosis (Mycobacterium bovis: referred to below as bTB) in UK cattle herds has increased from 0.05% in the late 1970s to 2.7% in 2000 (MAFF,
* Corresponding author. Present address: CSL Research Unit, Woodchester Park, Nympsfield, Gloucs GL10 3UJ, UK. Tel.: þ44-1453-860-777. E-mail address: [email protected] (B.T. Garnett).
0168-1591/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 1 5 9 1 ( 0 2 ) 0 0 2 0 4 - 6
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2001). This has serious economic implications both for the farming industry and the public finances, and raises significant animal welfare concerns (Krebs et al., 1997). The Eurasian badger (Meles meles) is susceptible to bTB infection and is suspected of transmitting the disease to cattle in the UK and Ireland (Krebs et al., 1997). However, despite strong circumstantial evidence of a link between bTB in cattle and badgers, little is known about how the disease is transmitted. Research to date has concentrated on the risks to cattle from pasture contaminated with badger excreta (e.g. Brown, 1993; Hutchings and Harris, 1997, 1999) but other evidence suggests that cattle are averse to grazing near badger faeces and urine (Benham and Broom, 1991), unless forced to do so by high grazing pressure (Hutchings and Harris, 1997). In addition, M. bovis bacilli have a short lifespan on pasture, surviving for up to three and fourteen days on summer pastures, in urine and faeces, respectively (MAFF, 1979; Jackson et al., 1995). Cheeseman and Mallinson (1981) have proposed an alternative potential transmission route, involving the contamination of farm buildings with badger excretory products. This hypothesis initially stemmed from observations of two tuberculous badgers feeding and sheltering in buildings on cattle farms. Subsequently, during a recent radio-tracking study at Woodchester Park, Gloucestershire, South-West England (Garnett et al., 2002), at least 26 individual badgers from two social groups were observed entering farm buildings and feeding from cattle troughs. The badgers in question, which included three individuals known to be infected with bTB, climbed into feed troughs at heights of up to 70.5 cm (Garnett et al., in press). Accumulations of badger droppings were found in these feed troughs and further contamination may have occurred from urine, sputum, and draining abscesses. Whilst feeding from the troughs, badgers also occasionally came into close proximity to feeding cattle, raising the possibility of direct aerosol transmission of M. bovis. Other studies have also reported the use of cattle feed and water troughs by badgers (Muirhead et al., 1974; Sleeman and Mulcahy, 1993). In the UK, current government advice to farmers is that cattle troughs should be set above 80 cm in order to exclude badgers (MAFF, 1999a,b). However, no research has been conducted to investigate the climbing ability of badgers or to determine whether a height of 80 cm is a sufficient deterrent. The aim of the present study, therefore, was to determine the maximum height to which a cattle trough would need to be raised in order to make it inaccessible to badgers.
2. Materials and methods 2.1. Study site The study took place at Woodchester Park, Gloucestershire, in a 7 km2 study area consisting of a valley surrounded by farmland. The valley itself consisted of mixed woodland interspersed with short-grass pasture, while the surrounding farmland consisted mainly of pasture but also included some arable fields. The resident badger population consisted of 25 social groups that were the subject of an intensive capture-mark-recapture study (see Delahay et al., 2000).
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2.2. Capture and examination of badgers The study focused on two social groups (groups A and B) each containing 16 badgers. Badgers were captured in steel-mesh box-traps baited with peanuts, anaesthetised with ketamine hydrochloride at a dose rate of 20 mg kg1 (MacKintosh et al., 1976), weighed to the nearest 0.1 kg, and marked with a distinctive fur-clip on each flank, consisting of a combination of arrows, crosses, lines and squares (Stewart and MacDonald, 1997). Furclipping symbols were created by removing the dark outer guard hairs of the badger’s coat, leaving the pale under-fur exposed beneath. The resulting contrast between the two fur layers allowed visual identification at night when the badger’s coat was illuminated with infra-red light. Fur-clipping was not expected to compromise the animals’ thermoregulatory efficiency but, as a precaution, cubs were only fur-clipped after attaining 8 kg in weight. Samples of urine, faeces, sputum and pus from open bite wounds were taken from captured badgers for microbiological culture (Clifton-Hadley et al., 1993) and a blood sample was taken for the detection of antibodies to M. bovis using an ELISA test (Goodger et al., 1994). Positive culture and ELISA test results were taken as evidence of infection with, and exposure to, M. bovis, respectively (see Delahay et al., 2000). 2.3. Field trials A cattle feeding trough of standard half-drum design (184 cm long, 30 cm wide, 16 cm deep: Ritchie, Forfar, Scotland) was purchased for use in field trials. The legs of the trough were removed and replaced by four telescopic legs of 3.3-cm diameter steel tubing. These legs were smooth along their entire length to deny badgers any footholds. Each pair of legs was joined near the top by a horizontal bar, on which the trough itself rested (see Fig. 1). Data on badger visits to the trough were collected using a time-lapse video system and
Fig. 1. Female badger climbing into the experimental trough, which was set at a height of 85 cm.
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infra-red lighting. The camera was mounted on a tripod and placed 4.5 m from the trough, with a tripod-mounted infra-red light placed 2 m from the camera on either side. Continuous night-time footage was recorded on 4-h video tapes by setting the video recorder to 12-h time-lapse mode. 2.4. Procedure 2.4.1. Experiment 1 From 15th June to 15th September 2000 the trough and video surveillance equipment were positioned on level ground near to the main set of a badger social group (group A) that had had no prior access to cattle troughs. An area of soft mud and leaf litter was chosen to minimise any risk of injury to the badgers from falls. During routine trapping operations 11 badgers from this group were caught and fur-clipped. However, one of the marked animals disappeared shortly after the experiment began and was therefore excluded from subsequent analyses. Initially, the trough was left unbaited for 1 week to allow badgers to get used to its presence. It was then baited with peanuts for 3-day periods of filming, separated by periods varying from 1 to 14 days, when it was left unbaited in order to prevent the animals from becoming dependent on this unnatural source of food. Peanuts were used because they were a familiar food, having been used as bait for trapping. Initially, the height of the rim of the trough was set at 30 cm above ground level. The trough was then raised successively to heights of 45, 60, and 70 cm, respectively. It was only made available for one night at each of these heights since video recordings showed it to be readily accessible to most badgers. Thereafter, the trough was raised in further 5-cm increments, but the height was only increased when at least one individual had successfully climbed it. The experiment was terminated, and the highest accessible height judged to have been reached, when all badgers had refused to attempt climbing, or had attempted and failed to access the trough, on at least five occasions. 2.4.2. Experiment 2 Experiment 1 was designed to reveal the climbing potential of free-living badgers that lacked previous experience of cattle troughs. However, it could be argued that since the trough was first made available at a low height and was then progressively raised, these badgers had the opportunity to develop climbing skills during the course of the experiment. To control for this possibility, in Experiment 2 the baited trough was set at a height of 81 cm and placed at the main set of a second social group (group B). The height of 81 cm was chosen because official advice to farmers is that troughs raised to a height of over 80 cm should be inaccessible to badgers (MAFF, 1999a,b). The trough was left unbaited at the set for a week to allow the badgers to habituate to it, before baiting it and recording on videotape behaviour over a single night. 2.5. Behavioural classification and analysis A climbing attempt was deemed successful if a badger managed to gain a secure footing within the basin of the feeding trough. A failure was classified as any attempt during which
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the badger raised all four feet off the ground simultaneously but came back to ground without drawing its entire body into the trough basin, or lost its footing on all four feet and slipped onto its back or side. The influence of individual body weight on climbing ability was investigated using measurements taken during routine trapping operations in the 2 weeks prior to the experiment.
3. Results When the trough was set at a height of 30 cm, all 10 individually identifiable members of group A, plus at least four cubs, managed to climb into it on the first night. Thereafter, as the height of the trough was raised, the number of badgers successfully accessing it gradually declined until, at 80 cm, only two animals were successful (Fig. 2). Thereafter, there was a slight reversal of the downward trend, but at heights above 95 cm only one cub still managed to climb into the trough. This animal was finally deterred at a height of 120 cm. Badgers employed a range of techniques to feed from the trough. At a height of 30 cm, they could simply sit by the trough and eat. At 45 cm, they could reach the food by standing on their hind legs and resting their forepaws on the rim of the trough. At 60 cm, climbing was necessary for all but the largest males, and above 60 cm climbing was necessary for all badgers. Adults climbed the trough by standing or jumping and hooking their fore-claws over the trough rim or over one of the horizontal bars on which the trough rested, then swinging and hauling themselves up with their forelegs until their back legs could gain purchase on the trough rim (Fig. 1).
Fig. 2. Number of individually identifiable adult badgers, and minimum number of cubs, able successfully to access the experimental trough, as a function of trough height. Minimum number of cubs was recorded as the greatest number seen feeding simultaneously from the trough.
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Fig. 3. Relationship between the maximum height successfully climbed by individual badgers, and body weight.
From 110 to 115 cm, the single animal that was still successful managed to climb up the legs supporting the trough. It did this by opposing its fore- and hind-paws on the leg of the trough and then scaling upwards by moving each pair of paws alternately. With two to four such movements it could reach the trough rim or the horizontal bar on which the trough rested, and haul itself into the basin with its forelegs. The maximum height reached by individual badgers varied from 70 to 115 cm and was negatively correlated with body weight (Spearman test, rs ¼ 0:82, n ¼ 10, P < 0:01) (Fig. 3). One female that had tested positive for bTB managed to climb to a height of 95 cm, despite poor body condition and an inflamed lymph gland in her groin, which caused her to limp perceptibly. In Experiment 2, at least five badgers climbed into the trough on the first occasion that it was baited, at a height of 81 cm.
4. Discussion Recently published government guidelines for UK farmers recommend that cattle feed and water troughs be raised at least 80 cm off the ground in order to make them inaccessible to badgers (MAFF, 1999a,b). Our results, by contrast, show badgers climbing into and feeding from a trough that was set at heights of up to 115 cm. Since the trough was initially presented at a height of only 30 cm and was thereafter raised incrementally, it could be argued that the badgers were given the opportunity to improve their climbing skills, through learning, during the course of the experiment. However, in a second trial, in which the trough was presented to a different social group of badgers at a height of 81 cm, several animals succeeded in climbing into it on the first night that it was available. Thus, the climbing ability of badgers has been underestimated and troughs placed at a height of 80 cm are not safe, even from naive badgers.
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These results may have important implications for the spread of bTB to cattle. In a recent case study, badger droppings and urine, including droppings deposited by an animal known to be infected with bTB, were found in cattle troughs on a farm where a herd breakdown subsequently occurred (Garnett et al., 2002). In addition, when badgers eat cattle food they may contaminate it with saliva, pus from open lesions and other secretions, all of which can carry M. bovis bacilli (MAFF, 1979; Gallagher and Clifton-Hadley, 2000). The fact that badger body weight was negatively correlated with climbing success in our study might, paradoxically, mean that tuberculous badgers that are in poor body condition may be better at accessing troughs. Indeed, in the present study, an infected female that was in visibly poor condition managed to climb into the experimental trough at heights of up to 95 cm. Infected individuals may also be more motivated to feed from artificial resources such as cattle troughs and farm buildings (Cheeseman and Mallinson, 1981; Garnett et al., 2002). Badgers have been reported to climb stone walls, to access bird tables and to climb trees to heights of 5 m in order to raid bee and wasp nests (Neal and Cheeseman, 1996). Scaling of trees is done in a bear-like manner, whereby the animal grips the trunk with both forefeet, and both hind-feet, opposed to one another, and then shuffles upwards by moving each pair of feet alternately (Neal and Cheeseman, 1996). This technique was adapted to scale the smooth steel pole legs of the trough in the present study (of 3.3 cm diameter). Evidently the badger’s powerful limbs, plantigrade feet and long claws, which are primarily adapted for digging (Neal and Cheeseman, 1996), are also surprisingly effective for climbing. Making cattle troughs secure against badgers may require new designs of trough, rather than merely increasing the height to which troughs are raised off the ground. This is especially the case with troughs designed to feed calves, young heifers and bullocks, since raising such troughs sufficiently to deter badgers would make the food inaccessible to the livestock for which it is intended. Existing troughs could be modified by attaching a rolling bar to the trough rim, or a guard shield projecting from just below the trough. Alternatively some form of closed trough could be used, opening in response to a cow-collar transmitter or a pressure plate on the floor. These alternative trough designs are likely to deter badgers from climbing, but may require some further experimentation.
Acknowledgements This study forms part of a D.Phil. project by the first author, funded by the BBSRC. We thank the farmers and landowners in the Woodchester Park study area for their cooperation, the University of Sussex for the time-lapse camera and cattle trough, and Tony Hillman for electronics advice. We are also indebted to the field team at Woodchester Park for their expertise in trapping and handling badgers, and to the Veterinary Laboratories Agency and Audrey Harris for microbiological culture of clinical samples. All work involving badgers at Woodchester Park is carried out under Home Office licence and is subject to an internal ethical review process. We thank Chris Cheeseman, Lucy Rogers and Gavin Wilson for comments on an earlier draft.
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