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Effects of Merino flock size, paddock complexity and time of day on response to trained leaders
Small Ruminant Research 97 (2011) 35–40
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Effects of Merino flock size, paddock complexity and time of day on response to trained leaders Donnalee B. Taylor a,c,∗ , Ian R. Price b , Wendy Y. Brown a , Geoff N. Hinch a,c a b c
School of Environmental and Rural Sciences, University of New England, Armidale, NSW 2351, Australia School of Cognitive, Behavioural and Social Sciences – Psychology, University of New England, Armidale, NSW 2351, Australia Australian Sheep Industry Cooperative Research Centre, Armidale, NSW 2351, Australia
a r t i c l e
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Article history: Received 2 July 2010 Received in revised form 10 January 2011 Accepted 17 January 2011 Available online 16 February 2011 Keywords: Movement Leadership Learning Training
a b s t r a c t This study examined if Merino sheep trained to respond to a combined visual and auditory stimulus could influence the movement of naïve Merino sheep flocks when the stimulus was activated. Trained Merino ewes were mixed with naive ewes and wethers in three groups of different sizes. Group ratios were (trained:naïve) Small Mob (SM) 1:5 ratio (n = 18), Medium Mob (MM) 1:10 (n = 33) and Large Mob (LM) 1:15 (n = 48). These groups were tested in 2 phases of increasing complexity. The first phase examined the responses of the different sized flocks (SM, MM and LM) to leader-initiated movement in 3 visually open paddocks (OP) during morning and afternoon grazing. The second phase examined the response of two flocks (SM and LM) at similar times but in 3 visually complex paddocks (CP). Animal groups were tested on 1 day per week in each paddock at pseudo random times. One hundred percent of the SM, 73.5% of the MM and 70% of the LM approached within 6 m of the stimulus in the OP tests. In the CP 100% of the SM and 56.5% of the LM approached the stimulus. The LM’s proximity to the stimulus in some of the CP tests was more than 6 m, however, it was not significant compared to the other CP or OP tests. Sixty seven percent of the SM animals and 33% of the LM of naïve sheep were observed to initiate movement toward the stimulus after the 6 tests in phase one. At the end of the first phase of testing the proportion of naïve sheep observed to be eating the previously unknown grain (lupins) was SM 73%, MM 60% and LM 36%, suggesting that naïve sheep will learn to eat a novel grain by following trained animals. Sub-grouping of the flock in this study was not a hindrance to flock movement. This study demonstrated that sheep trained to respond to a stimulus do provide leadership when mixed with naive sheep flocks causing a flock to rapidly change position to congregate around an activated stimulus. These findings suggest that trained animals could be used to manipulate animal movement for farm management purposes. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Attracting sheep flocks to shelter to avoid weather extremes (particularly chill) has been an objective of many
∗ Corresponding author at: School of Environmental and Rural Sciences, University of New England, Armidale, NSW 2351, Australia. Tel.: +61 04 39 555 296. E-mail address: [email protected] (D.B. Taylor). 0921-4488/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2011.01.010
researchers and producers over the history of sheep production throughout the world. In Australia, Alexander et al. (1979) attempted to train recently shorn sheep to identify shelter by placing them in sheltered areas post shearing. Lynch et al. (1980) attempted a similar goal by placing shelter at camp sites and Egan et al. (1976), Lynch and Alexander (1976), and Alexander et al. (1980) all planted trees, shrubs and tall grass windbreaks on fence lines and within paddocks in an attempt to provide areas of shelter easily accessible to ewes. However, none of these
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D.B. Taylor et al. / Small Ruminant Research 97 (2011) 35–40
approaches was consistently successful in terms of sheep flocks utilizing these areas in times of severe weather conditions and there seems to be a general consensus that confining ewes to sheltered areas is the only consistent method of guaranteeing shelter use by ewes (Alexander et al., 1980; Egan et al., 1972; McLaughlin et al., 1970). It is widely accepted that sheep are readily trained to respond to visual and auditory stimuli associated with food, and recent studies (Taylor et al., 2010) have demonstrated that this ability can be utilised to train individual Merino sheep to respond to such cues. Given the gregarious nature of Merino sheep it seems possible that animals trained to respond to a stimulus may move to a stimulus placed in designated sheltered areas and provide leadership for the remainder of the flock. There appear to be no studies that have examined this possibility or the potential impact of trained leaders on flock movement. Social organization, sub-grouping, leadership and following behaviour of Merino sheep have all been described but little is known of the impact of flock size on leader initiated movement and sub-grouping. Early studies in rangeland environments suggested that undulating topography and/or light timber and shrubs may cause flocks to form sub-groups (Arnold and Pahl, 1967), but we know little about the impact of flock size and its interactions with environmental (visual) complexity on sub-group formation and leader/follower behaviours. The present experiment was designed to determine if flocks of naïve Merino sheep of different sizes would follow trained leaders to a particular area of a paddock. This was tested in 3 visually open and 3 visually complex paddocks, at different times during morning grazing and afternoon grazing (Squires, 1974). 2. Materials and methods 2.1. Ethics All research procedures and animal care were approved by the University of New England’s Animal Ethics Committee on approval numbers AEC08/057, AEC09/006 and AEC09/073 which conform to the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes. 2.2. Study location The experiment was carried out at the University of New England (UNE), Armidale, NSW, latitude: 30.52◦ S, longitude: 151.67◦ E and an altitude of 1008 m. The experiment was conducted in the winter (MayAugust) of 2009 during which the temperature ranged from −7 to 27 ◦ C and 190.6 mm of rain fell over the study period of 123 days. 2.3. Animal details and allocation Nine fine wool Merino ewes born in September 2007 and previously gentled and trained (at 11 months of age) to respond to visual and auditory stimuli (Taylor et al., 2010) were used as “leaders” in this experiment. An additional 90 naïve fine wool Merino ewes and wethers, contemporaries of the trained animals were obtained from the UNE Kirby Research Station flock at 20 months of age. None of these naïve sheep had previously been exposed to the visual and auditory stimuli nor to the lupin grain and did not demonstrate lupin eating behaviour. Prior to the experiment the ninety naive sheep were mixed with the trained sheep for a seven-day period. Subsequently three flocks were formed each consisting of three randomly chosen trained sheep plus additional naïve animals to make up a small mob (SM) of 15 naive sheep and 3 trained sheep (1:5 ratio of trained to naive), medium mob (MM) of 30 naive sheep and 3 trained sheep (1:10 ratio) and a large mob (LM) of 45 naive sheep and 3 trained sheep (1:15 ratio). Taylor et al. (2010) had previously
reported that in a control group of Merino sheep (n = 11) that received no training none of the animals approached the cue during T-maze testing; consequently a classical control group was not included in the following experiments. The trained animals were temporarily marked with ‘scourable branding fluid’ suitable for greasy wool (AS4054-1992) applied to the top of their heads and rumps. These markings allowed easy identification of these animals from a distance of approximately 1–2 km. The nine trained ewes chosen for this experiment had been trained 8 months previously and were “refreshed” to approach the visual and auditory stimulus on three separate days in an outdoor 30 m × 40 m area at Kirby Station by making lupin grain available (50–100 g) when the animals responded to the cue. 2.4. Animal management During the experiment all sheep were maintained at UNE’s Trevenna plots They were rotationally grazed across 5 paddocks which varied in size from 2 to 4 ha. Each paddock had high dry matter availability (>3000 kg DM/ha) of improved natural pasture, and a limited amount of tree shelter. Water was continuously available from a trough in each paddock. Normal husbandry practices were followed including bimonthly weighing; and drenching as needed. All sheep were shorn in late October (spring) of the previous year. 2.5. Stimulus apparatus The stimulus used to attract the trained ewes was made up of a control logic Lithium CR 2032 TM-619-series event timer with memory backup and capacity for 15 combinations of daily programs set to operate a feeder, flashing light and beeping sound (Taylor et al., 2010). The timer was set to run for 10–15 min before automatically shutting off. The feeder was reconfigured from earlier reports using a waterproof 90 mm polyvinyl chloride (PVC) tube feed hopper (9.5 cm diameter) to deliver up to 1037 grams (g) to the ground. Below the feed hopper a 1 m × 1 m2 patch of grass was cut short to allow easy access to the lupin grain. The stimulus was mounted 100 cm above the ground on a metal platform attached to a star-picket metal post. The feeder, stimulus and power supply leads were securely covered with reinforced polyurethane tubing (1.5–3 cm diameter) and/or placed in a wire mesh cage to prevent wire-chewing. Power was supplied by a 40 cm × 50 cm 10 W voltage rated solar panel placed in the paddock charging a 12 V deep-cycle battery. The stimulus equipment was positioned in the paddock the evening prior to the test. The experiment was conducted in 2 phases of increasing complexity; the first phase examined the responses of different size flocks (SM, MM & LM) placed in 3 visually open paddocks (paddock seen as a replication) twice a day (during morning and afternoon grazing). The second phase examined the responses of two flock sizes (SM & LM) twice a day (during morning and afternoon grazing), in 3 visually complex paddocks. As it was not possible to introduce new naive animals for each phase of the experiment an order of increasing complexity and remixing of groups at the end of each phase was used to reduce the likelihood of learning or habituation (Broom and Fraser, 2007). 2.6. Phase 1: open paddock during the day (OP) The experimental areas were made up of three 2 ha paddocks with similar topography which were chosen in random order for test days, each paddock being used only once per flock. The 3 flocks of sheep (SM, MM, LM) were rotated through the 3 paddocks and tested twice a day in each paddock on Tuesday or Thursday in the morning and afternoon for 3 weeks, a different paddock being used each week. Behaviour observations were conducted from a hill in a neighbouring paddock which created a natural amphitheatre (1–2 km from the paddocks), eliminating observer interference or influence. Positions of the flock were recorded prior to activation of the stimulus and thereafter every 5 min for a maximum of 30 min post-stimulus activation. Additionally, the number of sub-groups (defined as 3+ sheep) present prior to stimulus activation was recorded. Once the stimulus was activated the time taken for the sheep to reach within a 6 radius of the stimulus was recorded along with the number of sheep within that proximity. The first animal to initiate dispersal and time post stimulus activation as well as distances from the stimulus were also recorded. Each paddock was subdivided by a grid to form 12 areas of approximately 1680 m2 the corners of which were marked by Signet florescent orange (350G) painted star-pickets. The orange markers pro-
D.B. Taylor et al. / Small Ruminant Research 97 (2011) 35–40 vided a means of estimating animal location and proximity to stimulus during testing. The stimulus location was predetermined so as to avoid placement at camping and resting areas. The stimulus equipment was positioned the evening prior to the test and the stimulus was randomly activated at one of two times in the morning (1030 or 1130 h) and afternoon (1330 or 1430 h) so as to avoid the anticipation of a food reward (Church, 1984; Lincoln et al., 2002; Meck, 1983; Roberts, 1981). At the completion of the first phase of the experiment, the trained sheep were removed from the naive sheep flocks and the remaining naive animals were tested to determine the number of sheep that would eat the novel food item (lupin grain). Sheep were tested in a 21 m × 23 m enclosed outdoor area by using a line of 300 g of lupin grain placed on the ground. Approximately 10 naive sheep were released into the area at a time and observed for eating behaviour. The identity and number of animals who mouthed or ate the grain were recorded. 2.7. Phase 2: complex paddock during the day (CP) The second phase of the experiment involved a repetition of phase one but only the SM and LM which had the greatest contrasts in time to reach the stimulus and percentage of sheep at the stimulus. These animals were tested in 3 new paddocks which had three 15 m long × 110 cm high hessian barriers erected in the central area of each paddock to create visually complexity. Records and sequences of observations and use of stimulus were the same as phase one. 2.8. Statistical analysis The different flock sizes were compared on the following behavioural measures: time for the sheep to reach the stimulus, number of sheep with in a 6-m radius of the stimulus post-activation, number of sub-groups (3+ sheep) present prior to stimulus activation, the time taken for dispersal movement away from the stimulus post activation and the time taken for 25% of the flock to disperse >18 m from the stimulus post activation. These measures were analysed to examine the effects of time of day (morning grazing [AM] vs afternoon grazing [PM]), mob size (SM, MM and LM) and paddock type (OP and CP replicates). These data were analysed using Chisquare (2 ) test of association. Differences between the flock sizes in the percentage of naive animals eating lupins pre and post phase 1 were also analysed using Chi-square. The probability value required for significance was set at P < 0.05. Whether naive or trained sheep initiated movement to the stimulus, initiated dispersal movement away from the stimulus were analysed to examine the effects of time of day AM and PM, mob size and paddock type. These data were analysed using a Oneway ANOVA. The statistical analysis program JMP 8.Ink (SAS Institute Inc.) was used and the ANOVA significance levels were set at P = 0.05, and pair comparisons were made using Student’s t.
3. Results 3.1. Phase 1 The percentage of sheep approaching within a 6 m radius of the stimulus 5 min post activation (morning and afternoon tests combined) were SM 100% and MM 73% (P > 0.05, Table 1). Flock size differed significantly between SM with a mean 100% and LM 70% (2 = 7.86, P = 0.005, Table 1) approaching within 6 m and between MM with a mean 73% and LM 70% (2 = 8.23, P = 0.004, Table 1) approaching within 6 m of the stimulus. The difference between flock size was most pronounced in the morning when a smaller proportion of the LM approached within a 6 m radius of the stimulus (47%) compared with the afternoon tests 93% (P < 0.005). The mean times for the sheep to reach the stimulus (within a 6 m radius) in the morning and afternoon tests combined was 5 min SM, 7.5 min MM, and 12.5 min LM (Table 1). Differences between SM and MM were not sig-
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nificant however, the differences between MM and LM and SM and LM were significant (Table 1). Dispersal movement away from the stimulus (post activation) was initiated entirely by naïve sheep. In morning and afternoon tests combined the mean dispersal time occurred at 54.5 min SM, 38.5 min MM and 39.5 min LM after arrival. Differences were not significant between the flock sizes (P = 0.88, Table 1) nor were dispersal times between morning and afternoon. Dispersal of 25% of the group post stimulus activation to greater than 18 m away from the stimulus took a mean 76.5 min for the SM, a mean 54 min for the MM and 55 min for the LM (P > 0.05, Table 1). Sub-group formation (3+ sheep) did not differ significantly between morning and afternoon test and ranged from 1 to 3 sub groups in all three flock sizes, only the large flock had 3 sub groups in any one test. Sub-group formation in the morning and afternoon test combined were 5 SM, 4.5 MM and 6 LM (Table 1). 3.2. Phase 2 The percentage of sheep approaching the stimulus within a 6 m radius 5 min post activation in the morning and afternoon tests combined were SM 100% compared to LM 56.5% (P < 0.05, Table 1). The SM flock animals approached within a 6 m radius of the stimulus on all occasions of CP test while the LM’s proximity to the stimulus in some of the CP tests was more than 6 m however, it was not significant compared to the other LM CP and OP tests. The mean time for the sheep to reach the stimulus (within a 6 m radius) in the morning and afternoon tests combined was 6 min SM and 13.5 min LM but the means were not significantly different (P > 0.05, Table 1). The number of times that naive sheep initiated movement to the stimulus post activation increased significantly (P < 0.005) across the tests. For the SM the increase was from 0 to 67% (10/15) while for the LM the increase was from 0% to 33% (15/45). Likewise the proportion of naive sheep demonstrating lupin-eating behaviour increased over time (P < 0.05) with 73% (11/15) of the SM flock demonstrating this behaviour compared with 36% for the LM flock. In the complex paddocks, the SM spent more time (P > 0.005) at the stimulus than the LM but there were no significant differences between morning and afternoon for either group. Dispersal of 25% of the group post stimulus activation to more than 18 m from the stimulus in the morning and afternoon test combined took a mean 25.8 min for the SM and a mean 15.6 min for the large flock and this difference was not significant (Table 1). The complex paddock during the day (CP) had a mean sub group number of 5.5 (SM) and 9.5 (LM) in the morning and afternoon test with a range from 1 to 2 (SM) and 2 to 4 (LM). These differences were also not significant (Table 1). Sub-group formation (3+ sheep) overall did not change significantly with increased flock size nor with paddock complexity (2 = 0.26, P > 0.05). 3.3. Learning The percentage of naive sheep that exhibited lupin eating behaviour after the initial 6 test events increased as
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D.B. Taylor et al. / Small Ruminant Research 97 (2011) 35–40
Table 1 Behavioural responses of flock to stimulus for small, medium and large mobs in the open paddocks (OP) and small and large mobs in the complex paddocks (CP) during morning grazing (AM) and afternoon grazing (PM). Behavioural measures
Mean time to reach stimulus (min) Percentage of sheep at stimulus (%) Number of sub-groups pre-stimulus activation Dispersal movement away from stimulus, mean time (min) Dispersal of 25% of group post stimulus activation >18 m away, mean time (min)
OP
CP
SM AM + PM
MM AM + PM
LM AM + PM
P-value
SM AM + PM
LM AM + PM
P-value
5b 100a 5a 54.5a
7.5b 73.5b 4.5a 38.5a
12.5a 70b 6a 39.5a
* * ns ns
6a 100a 5.5a 20a
13.5a 56.5b 9.5a 10a
ns * ns ns
76.5a
54a
55a
ns
25.8a
15.6a
ns
Different superscripts are significantly different; *P < 0.05; ns P > 0.05; AM + PM are an average of the 6 tests.
group size decreased (P < 0.05) ranging from 73% for the small flock (11/15), 60% (18/30) for MM and 36% (16/45) for the largest flock (LM). A total of 1037 g of lupin grain per stimulus exposure was used as a positive reinforcement in all three groups throughout the tests. Consequently the average amount of lupins available per animal was not equal in the three flocks: 57.6 g of lupins for SM, 31.4 g for MM and 21.6 g for LM. 4. Discussion This study has clearly demonstrated that sheep trained to respond to a combination of visual and auditory stimuli do provide leadership when mixed with naive sheep flocks and consequently can cause a flock to rapidly change position to congregate around an activated stimulus. This behaviour was consistently repeated for a variety of flock sizes, leader to flock ratios and in paddocks of varying complexity and at different times of day. The use of the same animals in phase 1 and 2 was not evaluated and possibly may have caused a learning effect even though the level of complexity was increased in the phase 2 paddocks. The relatively small paddocks used (2 ha) in this research may have facilitated the consistent responses obtained. In this study all three sizes of flock (SM, MM and LM) moved to the stimulus in the open paddocks and also the SM and LM in the complex paddocks. All sheep in the small flock approached the stimulus within a 6 m radius at both levels of complexity and it would appear that the trained sheep initiated flock movement through a combination of passive recruitment (Ramseyer et al., 2009) and allelomimetic behaviour (Scott, 1945). Gautrais et al. (2007) and Deneubourg and Goss (1989) have both noted that the probability of individual animals assuming a behaviour increased with the increased number of individuals exhibiting the behaviour although neither enunciated an ideal ratio for allelomimetic or recruitment behaviours to be initiated. In the present study it appears that three trained animals were sufficient to induce movement in flocks of between 15 and 45 animals. The gregarious nature of Merino sheep in particular (Lynch et al., 1989) and their social cohesiveness may have been a significant factor in the successful initiation of following behaviours of the whole flock. Interestingly, some of the individuals from the
naïve flock initiated movement and demonstrated lupin eating behaviour after the first phase of testing. This was particularly noticeable in the smaller flocks (SM & MM) which may reflect differences in the ratio of “teachers” to naïve animals (Lynch et al., 1983) but also might simply reflect the amount of “lupin reward” available for each sheep and the reinforcement effects of this reward (Carlson and Buskist, 1997). It is clear that through observational learning the naïve sheep learned to eat the novel food reward when reaching the stimulus which reinforced the link between reward and stimulus. This in turn allowed the naïve animals to begin to initiate flock movement. It would seem that in a practical context, a few trained animals would become “trainers” and passively “transmit” the behaviour to other animals. Similar learning has been reported by Burt (1943) who suggested that the habits, movement and home-range of wild sheep were learned from older ewes and passed across generations. The transfer of “resource knowledge” has been documented for other species including elephants Loxodonta Africana (Foley et al., 2008), ravens Corvus corax (Wright et al., 2003), and broad-winged hawks Buteo platypferus (Maransky and Bildstein, 2001). Dispersal of the flock from the stimulus area was consistently initiated by the naïve animals commencing around 15 min after arrival with 25% of the flock more than 18 m from the stimulus within 20 min. This time period is unlikely to be adequate to provide weather protection for prolonged periods and this dispersal was particularly notable in the larger flock. The reason for dispersal movement being initiated by naïve sheep may be linked with lower numbers receiving a food reward and/or a smaller food reward (57.61 g vs. 21.60 g) in the larger group. The success of operant conditioning is based on animals learning cause and effect relationships (Carlson and Buskist, 1997) and in particular these authors suggested that reward size influences the speed of learning presenting a likely reason for the slower learning observed in the larger flock. A significant impact of size of food reward has also been shown in studies with cattle and sheep (Bailey et al., 1989; Laca, 1995; Hewitson et al., 2005). To our knowledge the impact of paddock complexity on following behaviour has not previously been reported. The animals responded more quickly to the stimulus in the open paddock compared to the complex paddocks even
D.B. Taylor et al. / Small Ruminant Research 97 (2011) 35–40
though the same animals were used. The animals were possibly better trained by the complex paddock tests, however, response time was less on the CP indicating that complexity may be a factor to consider. The increased time to reach the stimulus in the complex paddocks may be associated with sheep being predominantly visual animals (Geist, 1971; Prince, 1956; Walls, 1942) and consequently if the stimulus was out of view the auditory stimulus would have been the only way for animals to orient themselves to the stimulus. The hessian visual barriers creating paddock complexity may have contributed to the increase in sub-grouping behaviour. Arnold and Pahl (1967) suggested that undulating topography and/or light timber will cause flocks to form sub-groups. Sub-grouping was increased slightly with complexity but not significantly so, but the increased complexity did reduce success rates particularly for the larger flock. However, once the sheep reached the stimulus they stayed in the area for a similar period of time (∼20 min) to phase one. This study has shown that trained sheep can be used to move flocks of naïve sheep in response to visual and auditory stimulus whether the ratio of trained to naïve sheep is 1:5, 1:10 or 1:15 and in paddocks of varying levels of complexity. The flocks of naïve sheep displayed observational learning to approach the stimulus suggesting sheep readily learn from their conspecifics which could potentially eliminate the need for training of all animals. The findings of this study suggest that trained animals could be used to move a flock to sheltered areas but further studies on less gregarious sheep breeds, group size (>45), larger paddocks (>20 ha), reward size, and the length of time animals can be kept at the stimulus site are still required. If these issues can be clarified then the use of an automated stimulus linked to weather alert systems based on expected chill levels (Geytenbeek, 1963; Lynch et al., 1980; NixonSmith, 1972) may be more widely incorporated into sheep husbandry practices. Acknowledgements The University of New England, Australian Wool Education Trust Fund and Sheep CRC generously funded this research. The UNE Science and Engineering Workshop team’s ingenious construction of trial equipment was greatly appreciated. The authors also extend their appreciation to Paul A. Arnott, Neil D. Baillie, Graham A. Chaffey, Brad K. Dawson, Mark D. Porter and Michael G. Raue for their assistance in trial setup, equipment and animal care. References Alexander, G., Lynch, J.J., Mottershead, B.E., 1979. Use of shelter and selection of lambing sites by shorn and unshorn ewes in paddocks with closely or widely spaced shelters. Appl. Anim. Ethol. 5, 51–69. Alexander, G., Lynch, J.J., Mottershead, B.E., Donnelly, J.B., 1980. Reduction in lamb mortality by means of grass wind-breaks: results of a five-year study. Proc. Austr. Soc. Anim. Prod. 13, 329–332. Arnold, G.W., Pahl, P.J., 1967. Sub-grouping in sheep flocks. Proc. Ecol. Soc. Austr. 2, 183–189.
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Small Ruminant Research journal homepage: www.elsevier.com/locate/smallrumres
Effects of Merino flock size, paddock complexity and time of day on response to trained leaders Donnalee B. Taylor a,c,∗ , Ian R. Price b , Wendy Y. Brown a , Geoff N. Hinch a,c a b c
School of Environmental and Rural Sciences, University of New England, Armidale, NSW 2351, Australia School of Cognitive, Behavioural and Social Sciences – Psychology, University of New England, Armidale, NSW 2351, Australia Australian Sheep Industry Cooperative Research Centre, Armidale, NSW 2351, Australia
a r t i c l e
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Article history: Received 2 July 2010 Received in revised form 10 January 2011 Accepted 17 January 2011 Available online 16 February 2011 Keywords: Movement Leadership Learning Training
a b s t r a c t This study examined if Merino sheep trained to respond to a combined visual and auditory stimulus could influence the movement of naïve Merino sheep flocks when the stimulus was activated. Trained Merino ewes were mixed with naive ewes and wethers in three groups of different sizes. Group ratios were (trained:naïve) Small Mob (SM) 1:5 ratio (n = 18), Medium Mob (MM) 1:10 (n = 33) and Large Mob (LM) 1:15 (n = 48). These groups were tested in 2 phases of increasing complexity. The first phase examined the responses of the different sized flocks (SM, MM and LM) to leader-initiated movement in 3 visually open paddocks (OP) during morning and afternoon grazing. The second phase examined the response of two flocks (SM and LM) at similar times but in 3 visually complex paddocks (CP). Animal groups were tested on 1 day per week in each paddock at pseudo random times. One hundred percent of the SM, 73.5% of the MM and 70% of the LM approached within 6 m of the stimulus in the OP tests. In the CP 100% of the SM and 56.5% of the LM approached the stimulus. The LM’s proximity to the stimulus in some of the CP tests was more than 6 m, however, it was not significant compared to the other CP or OP tests. Sixty seven percent of the SM animals and 33% of the LM of naïve sheep were observed to initiate movement toward the stimulus after the 6 tests in phase one. At the end of the first phase of testing the proportion of naïve sheep observed to be eating the previously unknown grain (lupins) was SM 73%, MM 60% and LM 36%, suggesting that naïve sheep will learn to eat a novel grain by following trained animals. Sub-grouping of the flock in this study was not a hindrance to flock movement. This study demonstrated that sheep trained to respond to a stimulus do provide leadership when mixed with naive sheep flocks causing a flock to rapidly change position to congregate around an activated stimulus. These findings suggest that trained animals could be used to manipulate animal movement for farm management purposes. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Attracting sheep flocks to shelter to avoid weather extremes (particularly chill) has been an objective of many
∗ Corresponding author at: School of Environmental and Rural Sciences, University of New England, Armidale, NSW 2351, Australia. Tel.: +61 04 39 555 296. E-mail address: [email protected] (D.B. Taylor). 0921-4488/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2011.01.010
researchers and producers over the history of sheep production throughout the world. In Australia, Alexander et al. (1979) attempted to train recently shorn sheep to identify shelter by placing them in sheltered areas post shearing. Lynch et al. (1980) attempted a similar goal by placing shelter at camp sites and Egan et al. (1976), Lynch and Alexander (1976), and Alexander et al. (1980) all planted trees, shrubs and tall grass windbreaks on fence lines and within paddocks in an attempt to provide areas of shelter easily accessible to ewes. However, none of these
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approaches was consistently successful in terms of sheep flocks utilizing these areas in times of severe weather conditions and there seems to be a general consensus that confining ewes to sheltered areas is the only consistent method of guaranteeing shelter use by ewes (Alexander et al., 1980; Egan et al., 1972; McLaughlin et al., 1970). It is widely accepted that sheep are readily trained to respond to visual and auditory stimuli associated with food, and recent studies (Taylor et al., 2010) have demonstrated that this ability can be utilised to train individual Merino sheep to respond to such cues. Given the gregarious nature of Merino sheep it seems possible that animals trained to respond to a stimulus may move to a stimulus placed in designated sheltered areas and provide leadership for the remainder of the flock. There appear to be no studies that have examined this possibility or the potential impact of trained leaders on flock movement. Social organization, sub-grouping, leadership and following behaviour of Merino sheep have all been described but little is known of the impact of flock size on leader initiated movement and sub-grouping. Early studies in rangeland environments suggested that undulating topography and/or light timber and shrubs may cause flocks to form sub-groups (Arnold and Pahl, 1967), but we know little about the impact of flock size and its interactions with environmental (visual) complexity on sub-group formation and leader/follower behaviours. The present experiment was designed to determine if flocks of naïve Merino sheep of different sizes would follow trained leaders to a particular area of a paddock. This was tested in 3 visually open and 3 visually complex paddocks, at different times during morning grazing and afternoon grazing (Squires, 1974). 2. Materials and methods 2.1. Ethics All research procedures and animal care were approved by the University of New England’s Animal Ethics Committee on approval numbers AEC08/057, AEC09/006 and AEC09/073 which conform to the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes. 2.2. Study location The experiment was carried out at the University of New England (UNE), Armidale, NSW, latitude: 30.52◦ S, longitude: 151.67◦ E and an altitude of 1008 m. The experiment was conducted in the winter (MayAugust) of 2009 during which the temperature ranged from −7 to 27 ◦ C and 190.6 mm of rain fell over the study period of 123 days. 2.3. Animal details and allocation Nine fine wool Merino ewes born in September 2007 and previously gentled and trained (at 11 months of age) to respond to visual and auditory stimuli (Taylor et al., 2010) were used as “leaders” in this experiment. An additional 90 naïve fine wool Merino ewes and wethers, contemporaries of the trained animals were obtained from the UNE Kirby Research Station flock at 20 months of age. None of these naïve sheep had previously been exposed to the visual and auditory stimuli nor to the lupin grain and did not demonstrate lupin eating behaviour. Prior to the experiment the ninety naive sheep were mixed with the trained sheep for a seven-day period. Subsequently three flocks were formed each consisting of three randomly chosen trained sheep plus additional naïve animals to make up a small mob (SM) of 15 naive sheep and 3 trained sheep (1:5 ratio of trained to naive), medium mob (MM) of 30 naive sheep and 3 trained sheep (1:10 ratio) and a large mob (LM) of 45 naive sheep and 3 trained sheep (1:15 ratio). Taylor et al. (2010) had previously
reported that in a control group of Merino sheep (n = 11) that received no training none of the animals approached the cue during T-maze testing; consequently a classical control group was not included in the following experiments. The trained animals were temporarily marked with ‘scourable branding fluid’ suitable for greasy wool (AS4054-1992) applied to the top of their heads and rumps. These markings allowed easy identification of these animals from a distance of approximately 1–2 km. The nine trained ewes chosen for this experiment had been trained 8 months previously and were “refreshed” to approach the visual and auditory stimulus on three separate days in an outdoor 30 m × 40 m area at Kirby Station by making lupin grain available (50–100 g) when the animals responded to the cue. 2.4. Animal management During the experiment all sheep were maintained at UNE’s Trevenna plots They were rotationally grazed across 5 paddocks which varied in size from 2 to 4 ha. Each paddock had high dry matter availability (>3000 kg DM/ha) of improved natural pasture, and a limited amount of tree shelter. Water was continuously available from a trough in each paddock. Normal husbandry practices were followed including bimonthly weighing; and drenching as needed. All sheep were shorn in late October (spring) of the previous year. 2.5. Stimulus apparatus The stimulus used to attract the trained ewes was made up of a control logic Lithium CR 2032 TM-619-series event timer with memory backup and capacity for 15 combinations of daily programs set to operate a feeder, flashing light and beeping sound (Taylor et al., 2010). The timer was set to run for 10–15 min before automatically shutting off. The feeder was reconfigured from earlier reports using a waterproof 90 mm polyvinyl chloride (PVC) tube feed hopper (9.5 cm diameter) to deliver up to 1037 grams (g) to the ground. Below the feed hopper a 1 m × 1 m2 patch of grass was cut short to allow easy access to the lupin grain. The stimulus was mounted 100 cm above the ground on a metal platform attached to a star-picket metal post. The feeder, stimulus and power supply leads were securely covered with reinforced polyurethane tubing (1.5–3 cm diameter) and/or placed in a wire mesh cage to prevent wire-chewing. Power was supplied by a 40 cm × 50 cm 10 W voltage rated solar panel placed in the paddock charging a 12 V deep-cycle battery. The stimulus equipment was positioned in the paddock the evening prior to the test. The experiment was conducted in 2 phases of increasing complexity; the first phase examined the responses of different size flocks (SM, MM & LM) placed in 3 visually open paddocks (paddock seen as a replication) twice a day (during morning and afternoon grazing). The second phase examined the responses of two flock sizes (SM & LM) twice a day (during morning and afternoon grazing), in 3 visually complex paddocks. As it was not possible to introduce new naive animals for each phase of the experiment an order of increasing complexity and remixing of groups at the end of each phase was used to reduce the likelihood of learning or habituation (Broom and Fraser, 2007). 2.6. Phase 1: open paddock during the day (OP) The experimental areas were made up of three 2 ha paddocks with similar topography which were chosen in random order for test days, each paddock being used only once per flock. The 3 flocks of sheep (SM, MM, LM) were rotated through the 3 paddocks and tested twice a day in each paddock on Tuesday or Thursday in the morning and afternoon for 3 weeks, a different paddock being used each week. Behaviour observations were conducted from a hill in a neighbouring paddock which created a natural amphitheatre (1–2 km from the paddocks), eliminating observer interference or influence. Positions of the flock were recorded prior to activation of the stimulus and thereafter every 5 min for a maximum of 30 min post-stimulus activation. Additionally, the number of sub-groups (defined as 3+ sheep) present prior to stimulus activation was recorded. Once the stimulus was activated the time taken for the sheep to reach within a 6 radius of the stimulus was recorded along with the number of sheep within that proximity. The first animal to initiate dispersal and time post stimulus activation as well as distances from the stimulus were also recorded. Each paddock was subdivided by a grid to form 12 areas of approximately 1680 m2 the corners of which were marked by Signet florescent orange (350G) painted star-pickets. The orange markers pro-
D.B. Taylor et al. / Small Ruminant Research 97 (2011) 35–40 vided a means of estimating animal location and proximity to stimulus during testing. The stimulus location was predetermined so as to avoid placement at camping and resting areas. The stimulus equipment was positioned the evening prior to the test and the stimulus was randomly activated at one of two times in the morning (1030 or 1130 h) and afternoon (1330 or 1430 h) so as to avoid the anticipation of a food reward (Church, 1984; Lincoln et al., 2002; Meck, 1983; Roberts, 1981). At the completion of the first phase of the experiment, the trained sheep were removed from the naive sheep flocks and the remaining naive animals were tested to determine the number of sheep that would eat the novel food item (lupin grain). Sheep were tested in a 21 m × 23 m enclosed outdoor area by using a line of 300 g of lupin grain placed on the ground. Approximately 10 naive sheep were released into the area at a time and observed for eating behaviour. The identity and number of animals who mouthed or ate the grain were recorded. 2.7. Phase 2: complex paddock during the day (CP) The second phase of the experiment involved a repetition of phase one but only the SM and LM which had the greatest contrasts in time to reach the stimulus and percentage of sheep at the stimulus. These animals were tested in 3 new paddocks which had three 15 m long × 110 cm high hessian barriers erected in the central area of each paddock to create visually complexity. Records and sequences of observations and use of stimulus were the same as phase one. 2.8. Statistical analysis The different flock sizes were compared on the following behavioural measures: time for the sheep to reach the stimulus, number of sheep with in a 6-m radius of the stimulus post-activation, number of sub-groups (3+ sheep) present prior to stimulus activation, the time taken for dispersal movement away from the stimulus post activation and the time taken for 25% of the flock to disperse >18 m from the stimulus post activation. These measures were analysed to examine the effects of time of day (morning grazing [AM] vs afternoon grazing [PM]), mob size (SM, MM and LM) and paddock type (OP and CP replicates). These data were analysed using Chisquare (2 ) test of association. Differences between the flock sizes in the percentage of naive animals eating lupins pre and post phase 1 were also analysed using Chi-square. The probability value required for significance was set at P < 0.05. Whether naive or trained sheep initiated movement to the stimulus, initiated dispersal movement away from the stimulus were analysed to examine the effects of time of day AM and PM, mob size and paddock type. These data were analysed using a Oneway ANOVA. The statistical analysis program JMP 8.Ink (SAS Institute Inc.) was used and the ANOVA significance levels were set at P = 0.05, and pair comparisons were made using Student’s t.
3. Results 3.1. Phase 1 The percentage of sheep approaching within a 6 m radius of the stimulus 5 min post activation (morning and afternoon tests combined) were SM 100% and MM 73% (P > 0.05, Table 1). Flock size differed significantly between SM with a mean 100% and LM 70% (2 = 7.86, P = 0.005, Table 1) approaching within 6 m and between MM with a mean 73% and LM 70% (2 = 8.23, P = 0.004, Table 1) approaching within 6 m of the stimulus. The difference between flock size was most pronounced in the morning when a smaller proportion of the LM approached within a 6 m radius of the stimulus (47%) compared with the afternoon tests 93% (P < 0.005). The mean times for the sheep to reach the stimulus (within a 6 m radius) in the morning and afternoon tests combined was 5 min SM, 7.5 min MM, and 12.5 min LM (Table 1). Differences between SM and MM were not sig-
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nificant however, the differences between MM and LM and SM and LM were significant (Table 1). Dispersal movement away from the stimulus (post activation) was initiated entirely by naïve sheep. In morning and afternoon tests combined the mean dispersal time occurred at 54.5 min SM, 38.5 min MM and 39.5 min LM after arrival. Differences were not significant between the flock sizes (P = 0.88, Table 1) nor were dispersal times between morning and afternoon. Dispersal of 25% of the group post stimulus activation to greater than 18 m away from the stimulus took a mean 76.5 min for the SM, a mean 54 min for the MM and 55 min for the LM (P > 0.05, Table 1). Sub-group formation (3+ sheep) did not differ significantly between morning and afternoon test and ranged from 1 to 3 sub groups in all three flock sizes, only the large flock had 3 sub groups in any one test. Sub-group formation in the morning and afternoon test combined were 5 SM, 4.5 MM and 6 LM (Table 1). 3.2. Phase 2 The percentage of sheep approaching the stimulus within a 6 m radius 5 min post activation in the morning and afternoon tests combined were SM 100% compared to LM 56.5% (P < 0.05, Table 1). The SM flock animals approached within a 6 m radius of the stimulus on all occasions of CP test while the LM’s proximity to the stimulus in some of the CP tests was more than 6 m however, it was not significant compared to the other LM CP and OP tests. The mean time for the sheep to reach the stimulus (within a 6 m radius) in the morning and afternoon tests combined was 6 min SM and 13.5 min LM but the means were not significantly different (P > 0.05, Table 1). The number of times that naive sheep initiated movement to the stimulus post activation increased significantly (P < 0.005) across the tests. For the SM the increase was from 0 to 67% (10/15) while for the LM the increase was from 0% to 33% (15/45). Likewise the proportion of naive sheep demonstrating lupin-eating behaviour increased over time (P < 0.05) with 73% (11/15) of the SM flock demonstrating this behaviour compared with 36% for the LM flock. In the complex paddocks, the SM spent more time (P > 0.005) at the stimulus than the LM but there were no significant differences between morning and afternoon for either group. Dispersal of 25% of the group post stimulus activation to more than 18 m from the stimulus in the morning and afternoon test combined took a mean 25.8 min for the SM and a mean 15.6 min for the large flock and this difference was not significant (Table 1). The complex paddock during the day (CP) had a mean sub group number of 5.5 (SM) and 9.5 (LM) in the morning and afternoon test with a range from 1 to 2 (SM) and 2 to 4 (LM). These differences were also not significant (Table 1). Sub-group formation (3+ sheep) overall did not change significantly with increased flock size nor with paddock complexity (2 = 0.26, P > 0.05). 3.3. Learning The percentage of naive sheep that exhibited lupin eating behaviour after the initial 6 test events increased as
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Table 1 Behavioural responses of flock to stimulus for small, medium and large mobs in the open paddocks (OP) and small and large mobs in the complex paddocks (CP) during morning grazing (AM) and afternoon grazing (PM). Behavioural measures
Mean time to reach stimulus (min) Percentage of sheep at stimulus (%) Number of sub-groups pre-stimulus activation Dispersal movement away from stimulus, mean time (min) Dispersal of 25% of group post stimulus activation >18 m away, mean time (min)
OP
CP
SM AM + PM
MM AM + PM
LM AM + PM
P-value
SM AM + PM
LM AM + PM
P-value
5b 100a 5a 54.5a
7.5b 73.5b 4.5a 38.5a
12.5a 70b 6a 39.5a
* * ns ns
6a 100a 5.5a 20a
13.5a 56.5b 9.5a 10a
ns * ns ns
76.5a
54a
55a
ns
25.8a
15.6a
ns
Different superscripts are significantly different; *P < 0.05; ns P > 0.05; AM + PM are an average of the 6 tests.
group size decreased (P < 0.05) ranging from 73% for the small flock (11/15), 60% (18/30) for MM and 36% (16/45) for the largest flock (LM). A total of 1037 g of lupin grain per stimulus exposure was used as a positive reinforcement in all three groups throughout the tests. Consequently the average amount of lupins available per animal was not equal in the three flocks: 57.6 g of lupins for SM, 31.4 g for MM and 21.6 g for LM. 4. Discussion This study has clearly demonstrated that sheep trained to respond to a combination of visual and auditory stimuli do provide leadership when mixed with naive sheep flocks and consequently can cause a flock to rapidly change position to congregate around an activated stimulus. This behaviour was consistently repeated for a variety of flock sizes, leader to flock ratios and in paddocks of varying complexity and at different times of day. The use of the same animals in phase 1 and 2 was not evaluated and possibly may have caused a learning effect even though the level of complexity was increased in the phase 2 paddocks. The relatively small paddocks used (2 ha) in this research may have facilitated the consistent responses obtained. In this study all three sizes of flock (SM, MM and LM) moved to the stimulus in the open paddocks and also the SM and LM in the complex paddocks. All sheep in the small flock approached the stimulus within a 6 m radius at both levels of complexity and it would appear that the trained sheep initiated flock movement through a combination of passive recruitment (Ramseyer et al., 2009) and allelomimetic behaviour (Scott, 1945). Gautrais et al. (2007) and Deneubourg and Goss (1989) have both noted that the probability of individual animals assuming a behaviour increased with the increased number of individuals exhibiting the behaviour although neither enunciated an ideal ratio for allelomimetic or recruitment behaviours to be initiated. In the present study it appears that three trained animals were sufficient to induce movement in flocks of between 15 and 45 animals. The gregarious nature of Merino sheep in particular (Lynch et al., 1989) and their social cohesiveness may have been a significant factor in the successful initiation of following behaviours of the whole flock. Interestingly, some of the individuals from the
naïve flock initiated movement and demonstrated lupin eating behaviour after the first phase of testing. This was particularly noticeable in the smaller flocks (SM & MM) which may reflect differences in the ratio of “teachers” to naïve animals (Lynch et al., 1983) but also might simply reflect the amount of “lupin reward” available for each sheep and the reinforcement effects of this reward (Carlson and Buskist, 1997). It is clear that through observational learning the naïve sheep learned to eat the novel food reward when reaching the stimulus which reinforced the link between reward and stimulus. This in turn allowed the naïve animals to begin to initiate flock movement. It would seem that in a practical context, a few trained animals would become “trainers” and passively “transmit” the behaviour to other animals. Similar learning has been reported by Burt (1943) who suggested that the habits, movement and home-range of wild sheep were learned from older ewes and passed across generations. The transfer of “resource knowledge” has been documented for other species including elephants Loxodonta Africana (Foley et al., 2008), ravens Corvus corax (Wright et al., 2003), and broad-winged hawks Buteo platypferus (Maransky and Bildstein, 2001). Dispersal of the flock from the stimulus area was consistently initiated by the naïve animals commencing around 15 min after arrival with 25% of the flock more than 18 m from the stimulus within 20 min. This time period is unlikely to be adequate to provide weather protection for prolonged periods and this dispersal was particularly notable in the larger flock. The reason for dispersal movement being initiated by naïve sheep may be linked with lower numbers receiving a food reward and/or a smaller food reward (57.61 g vs. 21.60 g) in the larger group. The success of operant conditioning is based on animals learning cause and effect relationships (Carlson and Buskist, 1997) and in particular these authors suggested that reward size influences the speed of learning presenting a likely reason for the slower learning observed in the larger flock. A significant impact of size of food reward has also been shown in studies with cattle and sheep (Bailey et al., 1989; Laca, 1995; Hewitson et al., 2005). To our knowledge the impact of paddock complexity on following behaviour has not previously been reported. The animals responded more quickly to the stimulus in the open paddock compared to the complex paddocks even
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though the same animals were used. The animals were possibly better trained by the complex paddock tests, however, response time was less on the CP indicating that complexity may be a factor to consider. The increased time to reach the stimulus in the complex paddocks may be associated with sheep being predominantly visual animals (Geist, 1971; Prince, 1956; Walls, 1942) and consequently if the stimulus was out of view the auditory stimulus would have been the only way for animals to orient themselves to the stimulus. The hessian visual barriers creating paddock complexity may have contributed to the increase in sub-grouping behaviour. Arnold and Pahl (1967) suggested that undulating topography and/or light timber will cause flocks to form sub-groups. Sub-grouping was increased slightly with complexity but not significantly so, but the increased complexity did reduce success rates particularly for the larger flock. However, once the sheep reached the stimulus they stayed in the area for a similar period of time (∼20 min) to phase one. This study has shown that trained sheep can be used to move flocks of naïve sheep in response to visual and auditory stimulus whether the ratio of trained to naïve sheep is 1:5, 1:10 or 1:15 and in paddocks of varying levels of complexity. The flocks of naïve sheep displayed observational learning to approach the stimulus suggesting sheep readily learn from their conspecifics which could potentially eliminate the need for training of all animals. The findings of this study suggest that trained animals could be used to move a flock to sheltered areas but further studies on less gregarious sheep breeds, group size (>45), larger paddocks (>20 ha), reward size, and the length of time animals can be kept at the stimulus site are still required. If these issues can be clarified then the use of an automated stimulus linked to weather alert systems based on expected chill levels (Geytenbeek, 1963; Lynch et al., 1980; NixonSmith, 1972) may be more widely incorporated into sheep husbandry practices. Acknowledgements The University of New England, Australian Wool Education Trust Fund and Sheep CRC generously funded this research. The UNE Science and Engineering Workshop team’s ingenious construction of trial equipment was greatly appreciated. The authors also extend their appreciation to Paul A. Arnott, Neil D. Baillie, Graham A. Chaffey, Brad K. Dawson, Mark D. Porter and Michael G. Raue for their assistance in trial setup, equipment and animal care. References Alexander, G., Lynch, J.J., Mottershead, B.E., 1979. Use of shelter and selection of lambing sites by shorn and unshorn ewes in paddocks with closely or widely spaced shelters. Appl. Anim. Ethol. 5, 51–69. Alexander, G., Lynch, J.J., Mottershead, B.E., Donnelly, J.B., 1980. Reduction in lamb mortality by means of grass wind-breaks: results of a five-year study. Proc. Austr. Soc. Anim. Prod. 13, 329–332. Arnold, G.W., Pahl, P.J., 1967. Sub-grouping in sheep flocks. Proc. Ecol. Soc. Austr. 2, 183–189.
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