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Spacing behaviour of sheep in pens
Applied Animal BehaviourScience, 12 (1984) 111--119
111
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
SPACING BEHAVIOUR OF SHEEP IN PENS
G.D. HUTSON
School of Agriculture and Forestry, University of Melbourne, ParkviUe, Vic. 3052
(Australia) (Accepted for publication 18 April 1983)
ABSTRACT Hutson, G.D., 1984. Spacing behaviour of sheep in pens. Appl. Anita. Behav. Sci., 12: 111--119. Photographs were taken of sheep in holding pens, with open or covered sides, containing 10, 30 or 50 sheep at a density of 10 sheep per 6 m 2. The data were analysed by computer to produce maps of pen use, distance moved and direction of facing of individual sheep, and distance and bearin_g to the nearest neighbouring sheep. Standing sheep were spaced evenly throughout the pen and were orientated parallel to, and facing in the same direction as, the nearest neighbour. Lying sheep selected positions at random in covered pens, but lay down parallel and next to the sides of open pens. Pen size had little effect on spacing behaviour. Covering pen sides restricted movement and promoted more uniform dispersion of lying sheep in the pen. The results suggest that the design of the transition zone from a pen to a race could be improved by allowing two or more sheep to enter the race in parallel.
INTRODUCTION
A problem often encountered in sheep handling is moving sheep from a holding pen into a race. It is generally assumed that sheep in a pen are orientated and spaced apart at random, whereas in a race they must all face in one direction. The experience of farmers suggests that the transition zone, where sheep move from a random to an aligned orientation, is the area where most difficulty is experienced in getting sheep to move freely, and where most force is needed. The aim of this study was to establish whether in fact sheep do space and align themselves at random in a holding pen. If not, then it might be possible to identify factors which could be useful in improving movement from pens to races. There have been no previous studies of spacing behaviour of sheep in pens, although Winfield et al. (1981) have described spatial behaviour in an open field, and Kilgour et al. (1975) have observed dispersal patterns of sheep in a paddock. Photographs were taken o f sheep held in pens, and the effect o f two corn-
0168-1591/84/$03.00
© 1984 Elsevier Science Publishers B.V.
112 mon variables, pen size and covering the pen sides, was examined. The data were analysed by computer to produce maps of pen use, the distance moved and direction of facing of individual sheep, and distance and bearing to the nearest neighbouring sheep. MATERIALS AND METHODS
Layout Three square holding pens, with side lengths of 2.5, 4.5 and 5.5 m, were made of steel mesh and positioned about 4 m apart around the N, E and S sides of a 5-m tower in a small, open paddock. The pens held 10, 30 or 50 sheep, at a common density of 10 sheep per 6 m 2. This is the recommended density for sheep in holding pens (Elliott and Ransom, 1975).
Animals One hundred cull ewes of various ages from a Corriedale flock were used. They were kept together as a group for 6 weeks prior to the start of the experiment.
Procedure On each test day, the sheep were brought into an adjacent yard and then randomly drafted into each of the 3 pens. The remaining 10 sheep were released. The sides of the pens were either left open or covered with hessian, according to a random schedule. Photographs of each pen were taken from the tower every 10 rain for a 2-h period, making 13 photographs per pen per session. This procedure was repeated over 10 days in a 2-week period, so that 5 replications of the 2 treatments, open or covered sides, were done. Data on wind speed and direction were available from a meteorological station about 300 m away.
Analysis The photographs were printed on 20 X 25 cm paper, and the Cartesian coordinates for the position of head, withers and rump of each animal were obtained using a grid on a clear plastic overlay. A computer programme was developed to analyse the location and orientation of each sheep. Similar programmes have been used by McCort and Graves (1978) and Pearson (1978) for the analysis of spatial data. The programme produced: (1) maps of the location of head coordinates in 50 × 50 cm squares for each pen; (2) the minimum distance moved by each individual from one photograph to the next; (3) the distance to the nearest neighbouring sheep; (4) the direction of facing of individual sheep, using the withers--
113 lO-sheep pen
3 0 - s h e e ppen
50-sheep pen
Covered sides
Lying
Open s~des
Covered sides
Raho observed/expected [] 0-0.5 [ ] 0.5-1.0
@ 1.o-,.s
•
15
•
>2'0
2.0
~
~_ N
Fig. 1. P e n use s h o w n as t h e ratio o f observed t o e x p e c t e d n u m b e r o f observa%ions per 5 0 X 5 0 c m square.
114 rump coordinates; (5) the bearing t o the nearest neighbour, which was the smallest angle an individual would have to turn through in order to be parallel to the nearest neighbour. RESULTS The data were analysed separately for lying and standing sheep. The maps of pen use (Fig. 1) show t h a t standing sheep tended to position themselves evenly t h r o u g h o u t the pen, regardless o f whether the sides were covered. Lying sheep, however, tended to lie next to the sides of the pen when t h e y
TABLE I Effect of covering pen sides on use of inside and outside 50 X 50 em squares. Observed frequencies are shown with expected values in parentheses Pen size
Sheep posture
Sides
50 sheep
Standing
Open
Lying
Standing
Open
Open Covered
Lying
Open Covered
10 sheep
Standing
Open Covered
Lying
Outside
1237 680 (1256) (661) Covered 1461 741 (1442) (760)
Covered 30 sheep
Inside
Open
G
1.50
P
NS
715 617 (790) (542) 696 352 (621) (427)
39.69
<0.01
745 574 (775) (544) 773 493 (743) (523)
5.74
<0.05
238 393 (304) (327) 396 288 (330) (364) 165 320 (178) (307) 177 268 (164) (281) 13
5 4 . 7 7 <0.01
3.31
NS
152
(36) (129) Covered
65
130
(42) (153)
37.06
<0.01
115
were open, but would lie in any location in the pen when the sides were covered. To test this observation statistically, a series of 2 X 2 G-tests were done, which compared the use of inside versus outside 50 × 50 cm squares in covered and open pens (Table I). Lying sheep in all 3 pens showed a significant preference for open outside squares. Standing sheep showed no such preference except in the 30~d~eep pen, where there was a small, but significant, preference for open outside squares. The total distance moved by each individual over the 13 photographs, regardless of whether it was standing or lying, was averaged for each treatm e n t (Table II). Analysis of variance showed that pen size (P ~ 0.001) and covering the pen sides (P ~ 0.01) had significant effects on distance moved. Sheep moved greater distances as pen size increased and when the sides of the pen were open. These effects were not the result of sheep lying down, because there were no significant differences in the proportion of sheep lying in the different treatments. TABLE II Effect of pen size and covering pen sides on mean distance (m) moved by individual sheep Replicate
Pen size 10 sheep
1 2 3 4 5 Mean
30 sheep
50 sheep
Open
Covered
Open
Covered
Open
Covered
8.29 7.45 6.18 11.00 7.57
8.23 5.99 4.64 4.87 6.52
12.48 9.35 10.52 7.30 10.86
8.70 9.46 8.83 7.87 8.99
14.18 11.76 9.31 10.50 9.61
10.14 8.42 8.46 9.79 10.00
8.10
6.05
10.10
8.77
11.07
9.36
There were clear differences between lying and standing sheep in their direction of facing. Sheep tended to lie down parallel to the pen sides, so that the frequency distributions for lying sheep showed peaks at 0, 90,180, 270 and 360 ° (Fig. 2). Although standing sheep had a similar tendency to align themselves parallel to the pen sides, especially in the small pen, the frequency distributions were more normally distributed about a common flock orientation -- 270 ° in 10~heep pens, 0--90 ° in 30~heep pens, and 90-180 ° in 50~heep pens. These orientations corresponded to the direction of the nearest adjacent pen of sheep. There was no association between flock orientation and speed or direction of the prevailing wind. There was no significant difference in the spacing between sheep in the 3 pen sizes, but standing sheep were significantly (P ~ 0.001) closer to the
116
1D-sheep pen Standing0s~::s
Covered sides
1
~ ~
!
]
30-sheep pen
~
~
,
,
.
90
180
270
,
,
50-sheep pen ,
5
Ul
90
180
2?0
360
0
360
0
90
180
270
.
,
,
360
Lying =1
Open sides
z
1
,
Covered
sides
5 o
go ,80 2~o ~3o
o
Qo ,8o 270 3eo
o
.o ~eo 270 3eo
Direction of facing (degrees) Fig. 2. Frequency distributions of direction of facing of individmd sheep in 10, 30 and 50-sheep pens. TABLE III Mean distances to the nearest neighbouring sheep (cm) for standing and lying sheep 10 sheep
Lying Standing
30 sheep
50 sheep
Open
Covered
Open
Covered
Open
Covered
57.4 52.3
57.2 53.3
58.1 54.9
58.2 53.0
57.4 52.3
57,2 53,3
nearest neighbouring sheep than were lying sheep (Table III). A quick test o f whether spacing is at random is to compare the mean nearest-neighbour distance with that expected in a random distribution (Clark and Evans, 1954). For 10 sheep in a pen at a density of 10 sheep per 6 m 2, the expected
117 15
Stan'ding
Open
Covered
sides
sides
10
f-
"~
!
15
!
Lying
I
I
i
Open
Covered
sides
sides
J~
z
5
-180
"90
0
!
!
90
180
Bearing to nearest
I
-180
-90
neighbour
0
90
180
(degrees)
Fig. 3. Frequency distributions of bearing to nearest neighbouring sheep for 50-sheep pens. Positive values refer to nearest neighbours on the right-hand side; negative values refer to the left-hand side.
nearest-neighbour distance is 38.7 cm, with 99% confidence limits o f 25.9-51~5 cm. All values in Table III exceed the upper limit, which indicates that the sheep are over
118 strategy according to whether they stand or lie down. Lying sheep select positions next to, and parallel with, the sides of open pens, whereas in covered pens, they appear to select positions at random. Standing sheep ate dispersed evenly throughout the pen, and adopt a typical spacing pattern of standing parallel to their nearest neighbour and usually facing in the same direction. Pen size appeared to have little effect on spacing behaviour. Nearestneighbour distances were unaffected, but individuals changed position more over the 2-h holding period in the larger pens. This was probably because greater space was available to move in, although sheep density remained the same.
Covering pen sides had interesting effects on spacing* behaviour. Sheep moved around the pen more when the sides were open, and lying sheep selected positions along the edges of the pen. It seems unlikely that lying sheep chose these locations to avoid trampling, as they did not do this in covered pens. Rather, the explanation for this behaviour seems to be related to the wide visual field of sheep. Previous experiments have demonstrated the importance of vision rather than auditory or olfactory senses when sheep move along races (Hutson, 1980; Franklin and Hutson, 1982). In open pens, edge positions may allow either a greater opportunity for visual exploration of the outside environment, or allow sheep to d e t e c t predators or other disturbances. Similarly, the greater movement observed in open pens may be related to this effect, with sheep changing position more often in order to look out of the pen. This is supported by the observation that the most c o m m o n flock orientations were those which allowed sheep to see other sheep in the nearest adjacent pen. The results have some practical implications for the design of sheep-holding pens. Where it is desirable to align sheep in one particu]~ direction, then open pens should be used. If, however, it is more desirable to obtain even utilization of the available pen space, then the sides should be covered. In many cases, this decision will depend upon the purpose and duration for which the sheep are held. The solution to the problem of transition-zone design is more difficult, but these results show that the natural, unaligned orientation of sheep is standing parallel to, and facing in the same direction as, neighbouring sheep. Thus, the most effective design may be one that encourages sheep to maintain this natural orientation. Races which allow two or more sheep to enter in parallel may therefore be more efficient than those which allow only one sheep at a time to enter. ACKNOWLEDGEMENTS This work was supported by a grant from the Wool Research Trust Fund on the recommendation of the Australian Wool Corporation. I would like to thank Michael Butler for assistance with collection and processing of the data and Peter Long for help with the computer analysis.
119 REFERENCES Clark, P.J. and Evans, F.C., 1954. Distance to nearest neighbour as a measure of spatial relationships in populations. Ecolo~z, 35: 445--453. Elliott, M. and Ransom, K., 1975. A guide to the design of sheep yards. J. Agric. (Victoria, Aust.), 73: 360--365. Franklin, J.R. and Hutson, G.D., 1982. Experiments on attracting sheep to move along a laneway. III. Visual stimuli. Apph Anim. Ethol., 8: 457---478. Hutson, G.D., 1980. Visual field, restricted vision and sheep movement in laneways. Appl. Anim. Ethoh, 6: 175--187. Kilgour, R., Pearson, A.J. and de Langen, H., 1975. Sheep dispersal patterns on hill country: techniques for study and analysis. Proc. N.Z. Soc. Anita. Prod., 35: 191--197. McCort, W.D. and Graves, H.B., 1978. A computer-assisted technique for processing spacing and orientation behaviour. Appl. Anim. Ethol., 4: 205--209. Pearson, A.J., 1978. PRS1 and PRS2: F O R T R A N programs for the analysis of animal spatialdata. Behav. Res. Methods Instrum., 10: 718--722. Winfield, C.G., Syme, G.J. and Pearson, A.J., 1981. Effect of familiaritywith each other and breed on the spatial behaviour of sheep in an open field.Apph Anim. Ethol., 7: 67--75.
111
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
SPACING BEHAVIOUR OF SHEEP IN PENS
G.D. HUTSON
School of Agriculture and Forestry, University of Melbourne, ParkviUe, Vic. 3052
(Australia) (Accepted for publication 18 April 1983)
ABSTRACT Hutson, G.D., 1984. Spacing behaviour of sheep in pens. Appl. Anita. Behav. Sci., 12: 111--119. Photographs were taken of sheep in holding pens, with open or covered sides, containing 10, 30 or 50 sheep at a density of 10 sheep per 6 m 2. The data were analysed by computer to produce maps of pen use, distance moved and direction of facing of individual sheep, and distance and bearin_g to the nearest neighbouring sheep. Standing sheep were spaced evenly throughout the pen and were orientated parallel to, and facing in the same direction as, the nearest neighbour. Lying sheep selected positions at random in covered pens, but lay down parallel and next to the sides of open pens. Pen size had little effect on spacing behaviour. Covering pen sides restricted movement and promoted more uniform dispersion of lying sheep in the pen. The results suggest that the design of the transition zone from a pen to a race could be improved by allowing two or more sheep to enter the race in parallel.
INTRODUCTION
A problem often encountered in sheep handling is moving sheep from a holding pen into a race. It is generally assumed that sheep in a pen are orientated and spaced apart at random, whereas in a race they must all face in one direction. The experience of farmers suggests that the transition zone, where sheep move from a random to an aligned orientation, is the area where most difficulty is experienced in getting sheep to move freely, and where most force is needed. The aim of this study was to establish whether in fact sheep do space and align themselves at random in a holding pen. If not, then it might be possible to identify factors which could be useful in improving movement from pens to races. There have been no previous studies of spacing behaviour of sheep in pens, although Winfield et al. (1981) have described spatial behaviour in an open field, and Kilgour et al. (1975) have observed dispersal patterns of sheep in a paddock. Photographs were taken o f sheep held in pens, and the effect o f two corn-
0168-1591/84/$03.00
© 1984 Elsevier Science Publishers B.V.
112 mon variables, pen size and covering the pen sides, was examined. The data were analysed by computer to produce maps of pen use, the distance moved and direction of facing of individual sheep, and distance and bearing to the nearest neighbouring sheep. MATERIALS AND METHODS
Layout Three square holding pens, with side lengths of 2.5, 4.5 and 5.5 m, were made of steel mesh and positioned about 4 m apart around the N, E and S sides of a 5-m tower in a small, open paddock. The pens held 10, 30 or 50 sheep, at a common density of 10 sheep per 6 m 2. This is the recommended density for sheep in holding pens (Elliott and Ransom, 1975).
Animals One hundred cull ewes of various ages from a Corriedale flock were used. They were kept together as a group for 6 weeks prior to the start of the experiment.
Procedure On each test day, the sheep were brought into an adjacent yard and then randomly drafted into each of the 3 pens. The remaining 10 sheep were released. The sides of the pens were either left open or covered with hessian, according to a random schedule. Photographs of each pen were taken from the tower every 10 rain for a 2-h period, making 13 photographs per pen per session. This procedure was repeated over 10 days in a 2-week period, so that 5 replications of the 2 treatments, open or covered sides, were done. Data on wind speed and direction were available from a meteorological station about 300 m away.
Analysis The photographs were printed on 20 X 25 cm paper, and the Cartesian coordinates for the position of head, withers and rump of each animal were obtained using a grid on a clear plastic overlay. A computer programme was developed to analyse the location and orientation of each sheep. Similar programmes have been used by McCort and Graves (1978) and Pearson (1978) for the analysis of spatial data. The programme produced: (1) maps of the location of head coordinates in 50 × 50 cm squares for each pen; (2) the minimum distance moved by each individual from one photograph to the next; (3) the distance to the nearest neighbouring sheep; (4) the direction of facing of individual sheep, using the withers--
113 lO-sheep pen
3 0 - s h e e ppen
50-sheep pen
Covered sides
Lying
Open s~des
Covered sides
Raho observed/expected [] 0-0.5 [ ] 0.5-1.0
@ 1.o-,.s
•
15
•
>2'0
2.0
~
~_ N
Fig. 1. P e n use s h o w n as t h e ratio o f observed t o e x p e c t e d n u m b e r o f observa%ions per 5 0 X 5 0 c m square.
114 rump coordinates; (5) the bearing t o the nearest neighbour, which was the smallest angle an individual would have to turn through in order to be parallel to the nearest neighbour. RESULTS The data were analysed separately for lying and standing sheep. The maps of pen use (Fig. 1) show t h a t standing sheep tended to position themselves evenly t h r o u g h o u t the pen, regardless o f whether the sides were covered. Lying sheep, however, tended to lie next to the sides of the pen when t h e y
TABLE I Effect of covering pen sides on use of inside and outside 50 X 50 em squares. Observed frequencies are shown with expected values in parentheses Pen size
Sheep posture
Sides
50 sheep
Standing
Open
Lying
Standing
Open
Open Covered
Lying
Open Covered
10 sheep
Standing
Open Covered
Lying
Outside
1237 680 (1256) (661) Covered 1461 741 (1442) (760)
Covered 30 sheep
Inside
Open
G
1.50
P
NS
715 617 (790) (542) 696 352 (621) (427)
39.69
<0.01
745 574 (775) (544) 773 493 (743) (523)
5.74
<0.05
238 393 (304) (327) 396 288 (330) (364) 165 320 (178) (307) 177 268 (164) (281) 13
5 4 . 7 7 <0.01
3.31
NS
152
(36) (129) Covered
65
130
(42) (153)
37.06
<0.01
115
were open, but would lie in any location in the pen when the sides were covered. To test this observation statistically, a series of 2 X 2 G-tests were done, which compared the use of inside versus outside 50 × 50 cm squares in covered and open pens (Table I). Lying sheep in all 3 pens showed a significant preference for open outside squares. Standing sheep showed no such preference except in the 30~d~eep pen, where there was a small, but significant, preference for open outside squares. The total distance moved by each individual over the 13 photographs, regardless of whether it was standing or lying, was averaged for each treatm e n t (Table II). Analysis of variance showed that pen size (P ~ 0.001) and covering the pen sides (P ~ 0.01) had significant effects on distance moved. Sheep moved greater distances as pen size increased and when the sides of the pen were open. These effects were not the result of sheep lying down, because there were no significant differences in the proportion of sheep lying in the different treatments. TABLE II Effect of pen size and covering pen sides on mean distance (m) moved by individual sheep Replicate
Pen size 10 sheep
1 2 3 4 5 Mean
30 sheep
50 sheep
Open
Covered
Open
Covered
Open
Covered
8.29 7.45 6.18 11.00 7.57
8.23 5.99 4.64 4.87 6.52
12.48 9.35 10.52 7.30 10.86
8.70 9.46 8.83 7.87 8.99
14.18 11.76 9.31 10.50 9.61
10.14 8.42 8.46 9.79 10.00
8.10
6.05
10.10
8.77
11.07
9.36
There were clear differences between lying and standing sheep in their direction of facing. Sheep tended to lie down parallel to the pen sides, so that the frequency distributions for lying sheep showed peaks at 0, 90,180, 270 and 360 ° (Fig. 2). Although standing sheep had a similar tendency to align themselves parallel to the pen sides, especially in the small pen, the frequency distributions were more normally distributed about a common flock orientation -- 270 ° in 10~heep pens, 0--90 ° in 30~heep pens, and 90-180 ° in 50~heep pens. These orientations corresponded to the direction of the nearest adjacent pen of sheep. There was no association between flock orientation and speed or direction of the prevailing wind. There was no significant difference in the spacing between sheep in the 3 pen sizes, but standing sheep were significantly (P ~ 0.001) closer to the
116
1D-sheep pen Standing0s~::s
Covered sides
1
~ ~
!
]
30-sheep pen
~
~
,
,
.
90
180
270
,
,
50-sheep pen ,
5
Ul
90
180
2?0
360
0
360
0
90
180
270
.
,
,
360
Lying =1
Open sides
z
1
,
Covered
sides
5 o
go ,80 2~o ~3o
o
Qo ,8o 270 3eo
o
.o ~eo 270 3eo
Direction of facing (degrees) Fig. 2. Frequency distributions of direction of facing of individmd sheep in 10, 30 and 50-sheep pens. TABLE III Mean distances to the nearest neighbouring sheep (cm) for standing and lying sheep 10 sheep
Lying Standing
30 sheep
50 sheep
Open
Covered
Open
Covered
Open
Covered
57.4 52.3
57.2 53.3
58.1 54.9
58.2 53.0
57.4 52.3
57,2 53,3
nearest neighbouring sheep than were lying sheep (Table III). A quick test o f whether spacing is at random is to compare the mean nearest-neighbour distance with that expected in a random distribution (Clark and Evans, 1954). For 10 sheep in a pen at a density of 10 sheep per 6 m 2, the expected
117 15
Stan'ding
Open
Covered
sides
sides
10
f-
"~
!
15
!
Lying
I
I
i
Open
Covered
sides
sides
J~
z
5
-180
"90
0
!
!
90
180
Bearing to nearest
I
-180
-90
neighbour
0
90
180
(degrees)
Fig. 3. Frequency distributions of bearing to nearest neighbouring sheep for 50-sheep pens. Positive values refer to nearest neighbours on the right-hand side; negative values refer to the left-hand side.
nearest-neighbour distance is 38.7 cm, with 99% confidence limits o f 25.9-51~5 cm. All values in Table III exceed the upper limit, which indicates that the sheep are over
118 strategy according to whether they stand or lie down. Lying sheep select positions next to, and parallel with, the sides of open pens, whereas in covered pens, they appear to select positions at random. Standing sheep ate dispersed evenly throughout the pen, and adopt a typical spacing pattern of standing parallel to their nearest neighbour and usually facing in the same direction. Pen size appeared to have little effect on spacing behaviour. Nearestneighbour distances were unaffected, but individuals changed position more over the 2-h holding period in the larger pens. This was probably because greater space was available to move in, although sheep density remained the same.
Covering pen sides had interesting effects on spacing* behaviour. Sheep moved around the pen more when the sides were open, and lying sheep selected positions along the edges of the pen. It seems unlikely that lying sheep chose these locations to avoid trampling, as they did not do this in covered pens. Rather, the explanation for this behaviour seems to be related to the wide visual field of sheep. Previous experiments have demonstrated the importance of vision rather than auditory or olfactory senses when sheep move along races (Hutson, 1980; Franklin and Hutson, 1982). In open pens, edge positions may allow either a greater opportunity for visual exploration of the outside environment, or allow sheep to d e t e c t predators or other disturbances. Similarly, the greater movement observed in open pens may be related to this effect, with sheep changing position more often in order to look out of the pen. This is supported by the observation that the most c o m m o n flock orientations were those which allowed sheep to see other sheep in the nearest adjacent pen. The results have some practical implications for the design of sheep-holding pens. Where it is desirable to align sheep in one particu]~ direction, then open pens should be used. If, however, it is more desirable to obtain even utilization of the available pen space, then the sides should be covered. In many cases, this decision will depend upon the purpose and duration for which the sheep are held. The solution to the problem of transition-zone design is more difficult, but these results show that the natural, unaligned orientation of sheep is standing parallel to, and facing in the same direction as, neighbouring sheep. Thus, the most effective design may be one that encourages sheep to maintain this natural orientation. Races which allow two or more sheep to enter in parallel may therefore be more efficient than those which allow only one sheep at a time to enter. ACKNOWLEDGEMENTS This work was supported by a grant from the Wool Research Trust Fund on the recommendation of the Australian Wool Corporation. I would like to thank Michael Butler for assistance with collection and processing of the data and Peter Long for help with the computer analysis.
119 REFERENCES Clark, P.J. and Evans, F.C., 1954. Distance to nearest neighbour as a measure of spatial relationships in populations. Ecolo~z, 35: 445--453. Elliott, M. and Ransom, K., 1975. A guide to the design of sheep yards. J. Agric. (Victoria, Aust.), 73: 360--365. Franklin, J.R. and Hutson, G.D., 1982. Experiments on attracting sheep to move along a laneway. III. Visual stimuli. Apph Anim. Ethol., 8: 457---478. Hutson, G.D., 1980. Visual field, restricted vision and sheep movement in laneways. Appl. Anim. Ethoh, 6: 175--187. Kilgour, R., Pearson, A.J. and de Langen, H., 1975. Sheep dispersal patterns on hill country: techniques for study and analysis. Proc. N.Z. Soc. Anita. Prod., 35: 191--197. McCort, W.D. and Graves, H.B., 1978. A computer-assisted technique for processing spacing and orientation behaviour. Appl. Anim. Ethol., 4: 205--209. Pearson, A.J., 1978. PRS1 and PRS2: F O R T R A N programs for the analysis of animal spatialdata. Behav. Res. Methods Instrum., 10: 718--722. Winfield, C.G., Syme, G.J. and Pearson, A.J., 1981. Effect of familiaritywith each other and breed on the spatial behaviour of sheep in an open field.Apph Anim. Ethol., 7: 67--75.