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A comparison of the role of vision and hearing in ewes finding their own lambs
Applied Animal Ethology, 4 (1978) 71-79 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
71
A COMPARISON OF THE ROLE OF VISION AND HEARING IN EWES FINDING THEIR OWN LAMBS
ELIZABETH
E. SHILLITO WALSER
Agricultural Research Council Institute CB2 4AT (Great Britain)
of Animal Physiology,
Babraham,
Cam bridge
(Received 7 February 1977)
ABSTRACT Shillito Walser, E.E., 1978. A comparison of the role of vision and hearing in ewes finding their own lambs. Appl. Anim. Ethol., 4: 71-79. Ewes of Clun Forest, Finnish, Jacob, Dalesbred and Soay breeds of sheep quickly identified, and ran to their lambs when given a choice of three litters of lambs 16 m away from the gate by which the ewes entered the experimental area. When the lambs were hidden behind canvas, less than half the ewes ran to their own lambs and they took much longer to reach them. Most of the ewes which did not stay near their own lambs, went away and did not stay by alien lambs. There was no significant difference between the breeds of sheep and no definite change in behaviour which was related to the age of the lamb.
INTRODUCTION
The bleating of lambs appears to be a call for attention, but whether their vocalisations are used in individual recognition by the ewes or just serve to orient the ewe towards the general direction of the lamb has been a matter of dispute. Lindsay and Fletcher (1968) claimed that the lamb’s bleat played no part in actual recognition. Morgan et al. (1975) worked with ewes that were deafened by surgery and blindfolded and found that hearing and sight were important in helping the ewe to locate her lamb, but they played no part in recognition. On the other hand, Alexander (1977) showed that by muting the lambs, recognition could be delayed and both Smith (1965) working with Masham and Clun Forest ewes and Poindron and Carrick (1976) working with Merinos have demonstrated that ewes display a significant preference for the bleating of their own lambs compared with the bleats from an alien lamb. This paper reports the results of experiments on ewes finding their lambs carried out in the springs of 1975 and 1976, similar to those reported on lambs finding their ewes (Shillito, 1975). Most lambs could find their mothers by using auditory clues when visual clues were not available.
72
METHODS
Ewes from five breeds of sheep (Table I) were used in the experiments. Animals of one breed were tested together in groups of three ewes with their lambs, but in repeated tests different animals made up each group when possible. All the ewes had lambed in fields adjacent to the experimental area and they were used to the presence of observers. The experimental area has been described by Shillito (1975). The observer stood outside the fence and recorded behaviour in writing. Ewes and lambs were separated for at least 0.5 h and usually 1 h before a series of tests began. The older age groups were separated for longer and, with the 41-50-day group in 1976, this was at least 3 h. It was necessary to separate the ewes and lambs to make sure that when they were released the ewes would search for their lambs.
TABLE
I
The number Breed
of tests made in each group according
to the age of the lamb
Number
of ewes tested
o-7
8-14
15-21
22-28
29-40
40+
Clun Forest Finnish Jacob Dalesbred Soay
18 5 14 3 16
11 10 13 3 11
10 11 15 3 12
10 11 14 3 10
12 18 17 3 11
17 17 17 3 21
78 72 90 18 81
Total
56
48
48
61
75
339
_
51
with lambs of different
~~~
ages (days)
Total number of tests
Procedure The lambs belonging to three ewes of the same breed were moved to the experimental area and put one in each pen. When a ewe had two lambs, they were put together in one pen, and ewes with twins were tested together. The ewes were then released in turn and allowed to run into the enclosure. The time taken for the ewe to run to her own lamb, or lambs, from the time of entry into the area was recorded by stop watch. A maximum of 120 s was allowed for each ewe to reach her lamb; after this time, or when the ewe had stood by a pen for at least 20 s continuously, the ewe was driven back to the holding pen. When all the ewes had run once, the lambs in the pens were always interchanged and canvas was tied round each pen so the ewes and lambs could not see each other. The ewes were released in turn again and their behaviour and the time taken to reach the correct lambs was recorded. Any change in
73
behaviour observed on this second trial was considered to be the effect of hiding the lambs from the ewes and was recorded as a “canvas effect”. The tests were repeated at weekly intervals for 6 weeks. The canvas was always used in the second trial because the ewes appeared to need a first trial with the lambs visible to train them to run to the pens at all. Ewes which stayed close to one pen continuously for 20 s were considered to have made a choice of lamb. If the ewe stayed close to the pen containing her lambs the trial was scored as a correct choice. If the ewe stayed close to a pen containing alien lambs, the trial was scored as a wrong choice and these results were later analysed to investigate the effect of the previous position of the lamb. Some ewes did not go near to the pens but stayed at least 4 m away. In these trials the results were scored as an incorrect response and recorded as “no choice”. NUMERICAL
RESULTS
Time to make a correct
response
The analysis of variance on the pooled data for all breeds showed that the ewes took significantly longer to make a correct response when the lambs were behind canvas than when the ewes could see the lambs. The average time taken to make a correct response was 13 s without the canvas and 40 s with the canvas (Table II), there being no significant change in the time to respond as the lambs aged (Fig.1). The Soay and Dalesbred ewes were faster than the Jacob, Finnish and Clun Forest ewes and the difference was close to the 5% level of significance (P = 0.07) (Table III), but the percentage of correct responses was smaller in the Dalesbred and the Soay ewes than in the other breeds when tested with the canvas. Percentage
of correct
responses
Considering the pooled data for all breeds, the ewes made 96% correct responses when they could see the lambs in comparison with 48% when the TABLE
II
Results of vocal recognition trials, showing the time taken for ewes to make a correct response and percentage of correct responses for all breeds (pooled data f S.E.) Pooled
data
Time to run (s) Percentage correct
?? P <
0.01.
Without
responses
13.6 96.6
canvas
+ 2.3 r 2.5
With canvas 40.3 47.9
f 2.a* * 2.5*
74
ear
Time
in days
from
lambing
Fig.1. The average time taken by ewes to make a correct response in recognition trials. Results pooled from ail breeds.
TABLE III Number of ewes making a correct response in vocal recognition trials according to individual breeds Breed
Clun Forest Finnish Jacob Dalesbred Soay
Number of trials
78 72 90 18 81
Without canvas
With canvas
Correct response (%)
Time (s)
Correct response (W)
Time (s)
96.5 94.0 94.9 100.0 97.6
11.3 13.3 13.7 11.1 18.5
54.4 57.7 45.2 38.9 43.2
45.5 45.5 48.6 28.9 32.7
r 4.0 t 4.3 f 3.7 f 8.2 + 3.9
+ 4.0 * 4.3 + 3.7 + 11.8 r 3.9
lambs were behind canvas. This difference was highly significant, P < 0.01. There was little change with the age of the lambs or difference between breeds. The results are shown in Table II and Fig.2 Analysis of incorrect
responses
with canvas
As half of the tests resulted in an incorrect response, it is interesting to analyse the results from the ewes which did not stay near to the pen containing their own lambs. Three quarters of the incorrect responses were classed as “no choice”, that is, the ewe did not stay near any pen. Some of the ewes with older lambs did not search for their lambs even though they had been separated for as long as 3 h. The remaining number of incorrect responses were made by ewes who stayed near to pens which held alien lambs. When these wrong choices were
75
gioo ++++&
without
canvas
g 00 E
I
Time in days from lambing
Fig.2. The percentage correct response made by ewes in recognition trials, in relation to age. Results pooled for all breeds.
analysed it was found that in 74% of the trials the ewes had gone to the position where their lambs had been visible before; so that 9% of all ewes tested went to the lamb’s previous position, Very few ewes made a completely wrong choice of lamb. The results are shown in Table IV. Silent lambs In some trials the lambs were silent, both when there was no canvas round the pen and when the canvas was up. All the Finnish and Dalesbred lambs were vocal when they could see the ewes, but one Clun Forest lamb, three Jacob lambs and six Soay lambs were silent under these conditions. The one Clun Forest and two of the Jacob ewes with silent lambs made a wrong choice even though the lamb was visible, but the third Jacob and all the Soay ewes did not make a mistake. When the canvas was round the pens and the lambs were silent, the ewes either made no choice at all and went away from the pens or they went to the pen in which their lambs had been visible before. The silent lambs in the Clun Forest and Finnish breeds were all in the first age group, O-7 days. The number of silent lambs in each breed is shown in Table IV in relation to the type of incorrect response made. More Soay lambs were silent than lambs of other breeds. BEHAVIOUR
Most of the ewes ran into the experimental area and then ran bleating to the pens in which the lambs were held. When the lambs were visible, it was impressive how quickly many ewes oriented to their own lambs so it appeared as if they ran straight from the entrance. Some ewes ran towards the pens and oriented from 4 m away, and some moved from pen to pen. Once the ewes had appeared to recognize their lambs, they stayed close, nosing through the
Total
Clun Forest Finnish Jacob Dalesbred Soay
Breed
Behaviour
TABLE IV response
1341177
31137 24131 44150 3/11 32148
Number
75.7
83.7 77.4 88.0 27.2 66.6
Per cent
21
4 1 4 0 12
No silent lambs
Ewes which made no choice
of ewes making an incorrect
32143
516 417 516 718 lo/16
Number
Previous
pen
74.4
83.3 71.4 83.3 87.5 62.5
Per cent
7
2 1 2 0 2
No silent lambs
Ewes which chose wrongly
when run with the canvas
11143
l/6 217 l/6 l/8 6/16
Number
Wrong pen
26.6
16.6 28.5 16.6 12.5 37.5
Per cent
0
0 0 0 0 0
No silent lambs
_
77
wires. Some of the ewes moved 1 m or so away and then returned to the pen as if to lead the lamb away, and then stayed close to the pen. Most lambs appeared to recognize their mothers quickly and came to the front of the pen bleating. The ewes made very few mistakes when they could see the lambs and most of the errors were made because the ewes did not go up near to the pens which held the lamb. Seventy-three per cent of the ewes which made a correct response went straight to the pen holding their own lamb and 27% went to the correct pen as a second choice. Of the ewes that went to the correct pen first, 87% oriented straight from the gate of the observation area. So it was clear that recognition with the lamb visible; was very rapid and accurate. There was no change with the age of the lambs up to 50 days of age. When the lambs were screened with canvas the ewes ran into the area bleating and paused. The lambs answered the ewes’ bleats and then the ewes oriented and approached. Some ewes did not get near to the pens and stood waiting about 4 m away. Some went up to the pens moving from one to the other and then they went away without making a choice. Some ewes went up to the pen in which their lambs were held and stayed there. One or two of the Clun Forest ewes always stood up on their hind legs and looked over the top of the canvas. Even though the ewes could not see their lambs, 69% of those who did identify them correctly went to the correct pen as a first choice and 60% of those oriented straight from the gate. The ewes took much longer to locate their lambs when they couldn’t see them and their performance was not very accurate. It seemed that the ewes needed a visual signal to stay close to the lambs as many of them went up to the pens but turned away and ended standing 16 m away at the far end of the area. This was particularly so when the lambs were older and the ewes seemed less likely to search for their lambs. DISCUSSION
In comparison with the ability of lambs to find their mothers when they were out of sight (Shillito, 1975), the ewes’ ability to find their lambs when they were out of sight was poorer (48% in comparison with 60%). In the field, the first response of the ewe to find her lamb is to stand and bleat. The lambs respond to the bleat and orient to the ewe and run to her when they are more than 2 days old. It is only if the lambs do not start running to the ewe, that the ewe starts to search for them. The conditions of the experiment demand that the ewes should search for their lambs and it seemed that some of the ewes needed the visual stimulus of a lamb to keep them near the pen when the lambs were behind the canvas. This might explain the high percentage of “no choice” results. In a high percentage of the wrong choices the ewes went to the pen where they had last seen their lambs. The results for the lambs were similar in that 10% of all the lambs tested showed this position effect, in comparison with
78
9% of all the ewes tested (Shillito, 1975). Returning to the lambs’ previous position is a characteristic behaviour pattern of many breeds of sheep and Alexander and Shillito (1977) found it in Merino sheep. It is unlikely that the ewes went to the pen because they could smell their lambs’ odour there. If they were using olfaction they would have made the correct choice because the lambs’scent would have been strongest at the pen site where they were present. The intention of the experiments was to demonstrate whether ewes could find their lambs by their voices when the lambs were out of sight. The results showed that 50% of the ewes could find their lambs. In some trials, the lambs did not bleat at all. When these silent lambs were visible, the Soay ewes found their lambs, as did one Jacob ewe, but the Clun ewe and one Jacob ewe did not find their lambs. The silent lambs behind the canvas were not found at all, which is to be expected unless scent alone could be used. The results from the silent lambs are significant because they demonstrate that without voice and sight the ewes were not able to locate their lambs, whereas with sight and no voice this was possible. It is very interesting that only 3% of the ewes tested made a completely wrong choice of lamb. Most of the ewes which were not able to find their lambs went away from the pens and made no choice at all. There was little difference between the breeds of sheep used in these trials, except that the Soay and Dalesbred ewes showed a tendency to make a correct choice more quickly than the other breeds when the lambs were behind the canvas. The Dalesbred ewes always searched for their lambs and, along with one or two of the Clun Forest ewes, sometimes tried to look over the top of the canvas. It seems that some ewes can use the sense of hearing to identify their lambs, 18 60
-
50
-
540 0 7 ; 30
-
81
I
90 70 -
72
-
E g20-
s
z
B
s,o-
QYs JZYSO UIL~OV) ’
0 CANVAS %
EFFECT
correct without
Numbers
I”
=
response _ 8 Time canvas
% correct response 8 Time with canvc~s
= No. of trials
Fig.3. The difference in time and percentage correct responses with and without canvas, made by the ewes of different breeds in recognition trials.
79
but visual stimuli are more important in assisting the ewe to approach the lamb and stay near. The lambs’ bleats attract attention and help the ewes to orient to the lambs’ positions, but as the voices of the lambs change as they grow older this may be one reason for the ewes not being very effective at finding the lambs when they were out of sight. It is possible thzt the effect of loss of visual contact with the lamb overrides other sensory information received. SUMMARY
(1) A method for testing the ability of ewes to find their lambs with or -uithout being able to see them is described. (2) Less than half the ewes tested were able to identify their lambs when they were out of sight and they took much longer to make a correct choice than when they could see the lambs. (3) There was no significant change in performance in relation to age. Ewes with older lambs made less effort to find their lambs than when the lambs were young. (4) There was no difference in behaviour between Clun Forest, Finn, Jacob, Soay and Dalesbred ewes, but the Soays and Dalesbred tended to choose their lambs more quickly than the other ewes. More of the Soay lambs were silent than in other breeds. ACKNOWLEDGEMENTS
I am grateful to Mr D.E. Walters of the Agricultural Research Council Statistics Unit, Downing Street, Cambridge, for carrying out the statistical analyses, and to Miss Christine Stride, Mr Peter Hague and Mr Paul Beck for helpful technical assistance. REFERENCES Alexander, G., 1977. Role of auditory and visual cues in mutual recognition between ewes and lambs in Merino sheep. Appl. Anim. Ethol., 3: 65-81. Alexander, G. and Shillito, E., 1977. The importance of odour, appearance and voice in maternal recognition of the young in Merino sheep (Ovis aries). Appl. Anim. Ethol., 3: 127-135. Lindsay, D.R. and Fletcher, I.C., 1968. Sensory involvement in the recognition of lambs by their dams. Anim. Behav., 16: 415-417. Morgan, P.D., Boundy, C.A.P., Arnold, G.W. and Lindsay, D.R., 1975. The roles played by the senses of the ewe in the location and recognition of lambs. Appl. Anim. Ethol., 1: 139-150. Poindron, P. and Carrick, M.J., 1976. Hearing recognition of the lamb by its mother. Anim. Behav., 24: 600-603. Shillito, E., 1975. A comparison of the role of vision and hearing in lambs finding their own dams. Appl. Anim. Ethol., 1: 369-377. Smith, F.V., 1965. Instinct and learning in the attachment of lamb and ewe. Anim. Behav., 13: 84-86.
71
A COMPARISON OF THE ROLE OF VISION AND HEARING IN EWES FINDING THEIR OWN LAMBS
ELIZABETH
E. SHILLITO WALSER
Agricultural Research Council Institute CB2 4AT (Great Britain)
of Animal Physiology,
Babraham,
Cam bridge
(Received 7 February 1977)
ABSTRACT Shillito Walser, E.E., 1978. A comparison of the role of vision and hearing in ewes finding their own lambs. Appl. Anim. Ethol., 4: 71-79. Ewes of Clun Forest, Finnish, Jacob, Dalesbred and Soay breeds of sheep quickly identified, and ran to their lambs when given a choice of three litters of lambs 16 m away from the gate by which the ewes entered the experimental area. When the lambs were hidden behind canvas, less than half the ewes ran to their own lambs and they took much longer to reach them. Most of the ewes which did not stay near their own lambs, went away and did not stay by alien lambs. There was no significant difference between the breeds of sheep and no definite change in behaviour which was related to the age of the lamb.
INTRODUCTION
The bleating of lambs appears to be a call for attention, but whether their vocalisations are used in individual recognition by the ewes or just serve to orient the ewe towards the general direction of the lamb has been a matter of dispute. Lindsay and Fletcher (1968) claimed that the lamb’s bleat played no part in actual recognition. Morgan et al. (1975) worked with ewes that were deafened by surgery and blindfolded and found that hearing and sight were important in helping the ewe to locate her lamb, but they played no part in recognition. On the other hand, Alexander (1977) showed that by muting the lambs, recognition could be delayed and both Smith (1965) working with Masham and Clun Forest ewes and Poindron and Carrick (1976) working with Merinos have demonstrated that ewes display a significant preference for the bleating of their own lambs compared with the bleats from an alien lamb. This paper reports the results of experiments on ewes finding their lambs carried out in the springs of 1975 and 1976, similar to those reported on lambs finding their ewes (Shillito, 1975). Most lambs could find their mothers by using auditory clues when visual clues were not available.
72
METHODS
Ewes from five breeds of sheep (Table I) were used in the experiments. Animals of one breed were tested together in groups of three ewes with their lambs, but in repeated tests different animals made up each group when possible. All the ewes had lambed in fields adjacent to the experimental area and they were used to the presence of observers. The experimental area has been described by Shillito (1975). The observer stood outside the fence and recorded behaviour in writing. Ewes and lambs were separated for at least 0.5 h and usually 1 h before a series of tests began. The older age groups were separated for longer and, with the 41-50-day group in 1976, this was at least 3 h. It was necessary to separate the ewes and lambs to make sure that when they were released the ewes would search for their lambs.
TABLE
I
The number Breed
of tests made in each group according
to the age of the lamb
Number
of ewes tested
o-7
8-14
15-21
22-28
29-40
40+
Clun Forest Finnish Jacob Dalesbred Soay
18 5 14 3 16
11 10 13 3 11
10 11 15 3 12
10 11 14 3 10
12 18 17 3 11
17 17 17 3 21
78 72 90 18 81
Total
56
48
48
61
75
339
_
51
with lambs of different
~~~
ages (days)
Total number of tests
Procedure The lambs belonging to three ewes of the same breed were moved to the experimental area and put one in each pen. When a ewe had two lambs, they were put together in one pen, and ewes with twins were tested together. The ewes were then released in turn and allowed to run into the enclosure. The time taken for the ewe to run to her own lamb, or lambs, from the time of entry into the area was recorded by stop watch. A maximum of 120 s was allowed for each ewe to reach her lamb; after this time, or when the ewe had stood by a pen for at least 20 s continuously, the ewe was driven back to the holding pen. When all the ewes had run once, the lambs in the pens were always interchanged and canvas was tied round each pen so the ewes and lambs could not see each other. The ewes were released in turn again and their behaviour and the time taken to reach the correct lambs was recorded. Any change in
73
behaviour observed on this second trial was considered to be the effect of hiding the lambs from the ewes and was recorded as a “canvas effect”. The tests were repeated at weekly intervals for 6 weeks. The canvas was always used in the second trial because the ewes appeared to need a first trial with the lambs visible to train them to run to the pens at all. Ewes which stayed close to one pen continuously for 20 s were considered to have made a choice of lamb. If the ewe stayed close to the pen containing her lambs the trial was scored as a correct choice. If the ewe stayed close to a pen containing alien lambs, the trial was scored as a wrong choice and these results were later analysed to investigate the effect of the previous position of the lamb. Some ewes did not go near to the pens but stayed at least 4 m away. In these trials the results were scored as an incorrect response and recorded as “no choice”. NUMERICAL
RESULTS
Time to make a correct
response
The analysis of variance on the pooled data for all breeds showed that the ewes took significantly longer to make a correct response when the lambs were behind canvas than when the ewes could see the lambs. The average time taken to make a correct response was 13 s without the canvas and 40 s with the canvas (Table II), there being no significant change in the time to respond as the lambs aged (Fig.1). The Soay and Dalesbred ewes were faster than the Jacob, Finnish and Clun Forest ewes and the difference was close to the 5% level of significance (P = 0.07) (Table III), but the percentage of correct responses was smaller in the Dalesbred and the Soay ewes than in the other breeds when tested with the canvas. Percentage
of correct
responses
Considering the pooled data for all breeds, the ewes made 96% correct responses when they could see the lambs in comparison with 48% when the TABLE
II
Results of vocal recognition trials, showing the time taken for ewes to make a correct response and percentage of correct responses for all breeds (pooled data f S.E.) Pooled
data
Time to run (s) Percentage correct
?? P <
0.01.
Without
responses
13.6 96.6
canvas
+ 2.3 r 2.5
With canvas 40.3 47.9
f 2.a* * 2.5*
74
ear
Time
in days
from
lambing
Fig.1. The average time taken by ewes to make a correct response in recognition trials. Results pooled from ail breeds.
TABLE III Number of ewes making a correct response in vocal recognition trials according to individual breeds Breed
Clun Forest Finnish Jacob Dalesbred Soay
Number of trials
78 72 90 18 81
Without canvas
With canvas
Correct response (%)
Time (s)
Correct response (W)
Time (s)
96.5 94.0 94.9 100.0 97.6
11.3 13.3 13.7 11.1 18.5
54.4 57.7 45.2 38.9 43.2
45.5 45.5 48.6 28.9 32.7
r 4.0 t 4.3 f 3.7 f 8.2 + 3.9
+ 4.0 * 4.3 + 3.7 + 11.8 r 3.9
lambs were behind canvas. This difference was highly significant, P < 0.01. There was little change with the age of the lambs or difference between breeds. The results are shown in Table II and Fig.2 Analysis of incorrect
responses
with canvas
As half of the tests resulted in an incorrect response, it is interesting to analyse the results from the ewes which did not stay near to the pen containing their own lambs. Three quarters of the incorrect responses were classed as “no choice”, that is, the ewe did not stay near any pen. Some of the ewes with older lambs did not search for their lambs even though they had been separated for as long as 3 h. The remaining number of incorrect responses were made by ewes who stayed near to pens which held alien lambs. When these wrong choices were
75
gioo ++++&
without
canvas
g 00 E
I
Time in days from lambing
Fig.2. The percentage correct response made by ewes in recognition trials, in relation to age. Results pooled for all breeds.
analysed it was found that in 74% of the trials the ewes had gone to the position where their lambs had been visible before; so that 9% of all ewes tested went to the lamb’s previous position, Very few ewes made a completely wrong choice of lamb. The results are shown in Table IV. Silent lambs In some trials the lambs were silent, both when there was no canvas round the pen and when the canvas was up. All the Finnish and Dalesbred lambs were vocal when they could see the ewes, but one Clun Forest lamb, three Jacob lambs and six Soay lambs were silent under these conditions. The one Clun Forest and two of the Jacob ewes with silent lambs made a wrong choice even though the lamb was visible, but the third Jacob and all the Soay ewes did not make a mistake. When the canvas was round the pens and the lambs were silent, the ewes either made no choice at all and went away from the pens or they went to the pen in which their lambs had been visible before. The silent lambs in the Clun Forest and Finnish breeds were all in the first age group, O-7 days. The number of silent lambs in each breed is shown in Table IV in relation to the type of incorrect response made. More Soay lambs were silent than lambs of other breeds. BEHAVIOUR
Most of the ewes ran into the experimental area and then ran bleating to the pens in which the lambs were held. When the lambs were visible, it was impressive how quickly many ewes oriented to their own lambs so it appeared as if they ran straight from the entrance. Some ewes ran towards the pens and oriented from 4 m away, and some moved from pen to pen. Once the ewes had appeared to recognize their lambs, they stayed close, nosing through the
Total
Clun Forest Finnish Jacob Dalesbred Soay
Breed
Behaviour
TABLE IV response
1341177
31137 24131 44150 3/11 32148
Number
75.7
83.7 77.4 88.0 27.2 66.6
Per cent
21
4 1 4 0 12
No silent lambs
Ewes which made no choice
of ewes making an incorrect
32143
516 417 516 718 lo/16
Number
Previous
pen
74.4
83.3 71.4 83.3 87.5 62.5
Per cent
7
2 1 2 0 2
No silent lambs
Ewes which chose wrongly
when run with the canvas
11143
l/6 217 l/6 l/8 6/16
Number
Wrong pen
26.6
16.6 28.5 16.6 12.5 37.5
Per cent
0
0 0 0 0 0
No silent lambs
_
77
wires. Some of the ewes moved 1 m or so away and then returned to the pen as if to lead the lamb away, and then stayed close to the pen. Most lambs appeared to recognize their mothers quickly and came to the front of the pen bleating. The ewes made very few mistakes when they could see the lambs and most of the errors were made because the ewes did not go up near to the pens which held the lamb. Seventy-three per cent of the ewes which made a correct response went straight to the pen holding their own lamb and 27% went to the correct pen as a second choice. Of the ewes that went to the correct pen first, 87% oriented straight from the gate of the observation area. So it was clear that recognition with the lamb visible; was very rapid and accurate. There was no change with the age of the lambs up to 50 days of age. When the lambs were screened with canvas the ewes ran into the area bleating and paused. The lambs answered the ewes’ bleats and then the ewes oriented and approached. Some ewes did not get near to the pens and stood waiting about 4 m away. Some went up to the pens moving from one to the other and then they went away without making a choice. Some ewes went up to the pen in which their lambs were held and stayed there. One or two of the Clun Forest ewes always stood up on their hind legs and looked over the top of the canvas. Even though the ewes could not see their lambs, 69% of those who did identify them correctly went to the correct pen as a first choice and 60% of those oriented straight from the gate. The ewes took much longer to locate their lambs when they couldn’t see them and their performance was not very accurate. It seemed that the ewes needed a visual signal to stay close to the lambs as many of them went up to the pens but turned away and ended standing 16 m away at the far end of the area. This was particularly so when the lambs were older and the ewes seemed less likely to search for their lambs. DISCUSSION
In comparison with the ability of lambs to find their mothers when they were out of sight (Shillito, 1975), the ewes’ ability to find their lambs when they were out of sight was poorer (48% in comparison with 60%). In the field, the first response of the ewe to find her lamb is to stand and bleat. The lambs respond to the bleat and orient to the ewe and run to her when they are more than 2 days old. It is only if the lambs do not start running to the ewe, that the ewe starts to search for them. The conditions of the experiment demand that the ewes should search for their lambs and it seemed that some of the ewes needed the visual stimulus of a lamb to keep them near the pen when the lambs were behind the canvas. This might explain the high percentage of “no choice” results. In a high percentage of the wrong choices the ewes went to the pen where they had last seen their lambs. The results for the lambs were similar in that 10% of all the lambs tested showed this position effect, in comparison with
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9% of all the ewes tested (Shillito, 1975). Returning to the lambs’ previous position is a characteristic behaviour pattern of many breeds of sheep and Alexander and Shillito (1977) found it in Merino sheep. It is unlikely that the ewes went to the pen because they could smell their lambs’ odour there. If they were using olfaction they would have made the correct choice because the lambs’scent would have been strongest at the pen site where they were present. The intention of the experiments was to demonstrate whether ewes could find their lambs by their voices when the lambs were out of sight. The results showed that 50% of the ewes could find their lambs. In some trials, the lambs did not bleat at all. When these silent lambs were visible, the Soay ewes found their lambs, as did one Jacob ewe, but the Clun ewe and one Jacob ewe did not find their lambs. The silent lambs behind the canvas were not found at all, which is to be expected unless scent alone could be used. The results from the silent lambs are significant because they demonstrate that without voice and sight the ewes were not able to locate their lambs, whereas with sight and no voice this was possible. It is very interesting that only 3% of the ewes tested made a completely wrong choice of lamb. Most of the ewes which were not able to find their lambs went away from the pens and made no choice at all. There was little difference between the breeds of sheep used in these trials, except that the Soay and Dalesbred ewes showed a tendency to make a correct choice more quickly than the other breeds when the lambs were behind the canvas. The Dalesbred ewes always searched for their lambs and, along with one or two of the Clun Forest ewes, sometimes tried to look over the top of the canvas. It seems that some ewes can use the sense of hearing to identify their lambs, 18 60
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I
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-
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0 CANVAS %
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Numbers
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=
response _ 8 Time canvas
% correct response 8 Time with canvc~s
= No. of trials
Fig.3. The difference in time and percentage correct responses with and without canvas, made by the ewes of different breeds in recognition trials.
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but visual stimuli are more important in assisting the ewe to approach the lamb and stay near. The lambs’ bleats attract attention and help the ewes to orient to the lambs’ positions, but as the voices of the lambs change as they grow older this may be one reason for the ewes not being very effective at finding the lambs when they were out of sight. It is possible thzt the effect of loss of visual contact with the lamb overrides other sensory information received. SUMMARY
(1) A method for testing the ability of ewes to find their lambs with or -uithout being able to see them is described. (2) Less than half the ewes tested were able to identify their lambs when they were out of sight and they took much longer to make a correct choice than when they could see the lambs. (3) There was no significant change in performance in relation to age. Ewes with older lambs made less effort to find their lambs than when the lambs were young. (4) There was no difference in behaviour between Clun Forest, Finn, Jacob, Soay and Dalesbred ewes, but the Soays and Dalesbred tended to choose their lambs more quickly than the other ewes. More of the Soay lambs were silent than in other breeds. ACKNOWLEDGEMENTS
I am grateful to Mr D.E. Walters of the Agricultural Research Council Statistics Unit, Downing Street, Cambridge, for carrying out the statistical analyses, and to Miss Christine Stride, Mr Peter Hague and Mr Paul Beck for helpful technical assistance. REFERENCES Alexander, G., 1977. Role of auditory and visual cues in mutual recognition between ewes and lambs in Merino sheep. Appl. Anim. Ethol., 3: 65-81. Alexander, G. and Shillito, E., 1977. The importance of odour, appearance and voice in maternal recognition of the young in Merino sheep (Ovis aries). Appl. Anim. Ethol., 3: 127-135. Lindsay, D.R. and Fletcher, I.C., 1968. Sensory involvement in the recognition of lambs by their dams. Anim. Behav., 16: 415-417. Morgan, P.D., Boundy, C.A.P., Arnold, G.W. and Lindsay, D.R., 1975. The roles played by the senses of the ewe in the location and recognition of lambs. Appl. Anim. Ethol., 1: 139-150. Poindron, P. and Carrick, M.J., 1976. Hearing recognition of the lamb by its mother. Anim. Behav., 24: 600-603. Shillito, E., 1975. A comparison of the role of vision and hearing in lambs finding their own dams. Appl. Anim. Ethol., 1: 369-377. Smith, F.V., 1965. Instinct and learning in the attachment of lamb and ewe. Anim. Behav., 13: 84-86.