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Changing colour preferences of chicks
Anim . Behav ., 1969, 17, 3-8
CHANGING COLOUR PREFERENCES OF CHICKS BY
ANN TAYLOR, W . SLUCKIN & ROSEMARY HEWITT Department of Psychology, University of Leicester
Young nidifugous birds readily show preferences for some colours over others . Thorndike (1911) observed domestic chicks pecking coloured spots, and Lashley (1916) studied the chick's approach responses to coloured surfaces . More recently, chicks' preferences for colours were investigated by Schaefer & Hess (1959), by Smith & Hoyes (1961), and by Smith & Meyer (1965) . Kear (1964) tested pecking preferences for colours in the young of many species of Anatidae and Phasianidae, and Weidmann (1965) similarly reported on young moorhens and coots . Findings of all these workers have been dependent not only on the methods of testing but also on the characteristics of the various colours used and especially on their luminosity (Kear, 1966) . Very few attempts have been made to study changes in preference rather than colour preferences as such . Gray (1961) attempted to study colour preferences of domestic fowl chicks as a function of maturation ; he reported that choices, as measured by approach responses, tended to change with age . Our own interest has been in the stability or otherwise of colour preferences in relation to various types of intervening experience . In our experiments we used as subjects domestic fowl and Japanese quail chicks . We tested them individually for approach preference between two given colours, and then tested each bird again in the same way after `training' of some kind with one or the other colour or after no training. Four experiments are reported . Experiment I is concerned with the efficacy of different methods of altering the domestic chicks' colour preferences . As `training' methods we used (a) exposure to coloured walls of rearing pens, (b) conventional imprinting and (c) a form of conditioning with heat as the unconditioned stimulus (UCS) . Experiment 2 is concerned with the variable of duration of experience, using only one method of effecting a shift of preference, namely the `exposure' procedure . Experiments 3 and 4 attempt to shed some light on the generality of the effects we have found . To this end we used a new pair of colours, and also experimented with a further species, the Japanese quail .
Experiment 1 Methods The subjects were 242 chicks hatched from `cobb' eggs in the laboratory ; 68 were assigned to the exposure group, 70 to the imprinting group, 64 to the conditioning and 40 to a control group . Each chick was moved from the incubator into a grey cardboard pen, 1 ft x 1 ft x 1 ft (30 cm 3), open at the top and heated by a 60 W radiant-heat bulb . A chick in the pen was visually isolated from other chicks, although it could hear them . Food and water were provided in each cage . After 24 hr each chick was removed from its pen and placed in a runway 22 in . (56 cm) long, 6 in . (15 cm) wide and 8 in . (20 cm) high . The floor was marked off in 1-in . (2 . 5 cm) strips ; the central line was labelled 0 and the lines to either side of it were numbered 1 to 11, line 1I coinciding with the end of the runway . Clipped to each end of the runway was a 6 in . (15 cm) square of coloured plastic ; one end was blue (Oroglass, Blue 2326, „ in . (3 mm) thick . and the other red (ICI Perspex Sheet 461) . All the coloured plastic used in these experiments was rubbed down with sand paper to minimize reflection . A light bulb was suspended directly above each end of the runway. A chick was placed in the runway on the zero line and facing a long side ; a stopwatch was started and the chick was observed on every minute for 5 min, and its position noted . If the chick was between lines 6 and 11 towards the red end of the runway, it was given a score of -{-1 ; if it was between lines 6 and I 1 towards the blue end, a score of -1 ; otherwise it received a score of 0 . Thus the total scores during the 5-min test ranged from +5 to -5 . A positive score was taken to indicate a perference for red, and a negative score a preference for blue . After this test the chick was removed from the runway for 2 hr, during which time it received the experimental or control treatment to which it had been assigned . At the end of 2 hr it was replaced in the runway and tested, and its behaviour scored, as before . For half the chicks in each group red was on the right of the entry point and blue on the left ; for the rest the positions were reversed . The colours for any
4
ANIMAL BEHAVIOUR, 17, 1
one chick were in the same position in both the pre-training and the post-training tests . Experimental procedures were as follows :
assigned alternately to red-training and bluetraining, not on the basis of their initial score .
(a) Exposure. After test 1 the chick was placed in a pen, 1 ft x 1 ft x 1 ft (30 cm 3), three sides of which were lined either with red or with blue Perspex. Water was available in the pen . Half the chicks were exposed to red in this way and half were exposed to blue .
It will be seen from Table I that a clear preference emerged on test 1 for red over blue, chicks in all groups showing essentially the same pattern . In no case were the proportions of redpreferring, blue-preferring and non-preferring birds different for red-training and blue-training groups .
(b) Imprinting . The chick was placed, after test 1, in a grey circular pen 18 in . (46 cm) in diameter and 12 in . (30 cm) high in which water was available . In the centre of the pen was a small synchronous motor driving a cam which switched on another synchronous motor for 21 sec and off for 31 sec. This motor caused a 2-in . (5 cm) square of Perspex (red or blue) to move round the pen at a height of I in . (2 . 5 cm) from the ground . The chick was given 2 hr inside the pen with the moving object . As expected, some chicks followed the Perspex square . (c) Conditioning. The conditioning apparatus consisted of one tank 18 in . x 18 in . x 81 in . (46 cm x 46 cm x 21 . 5 cm) inside another tank 20 in . x 20 in . x 81 in . (51 cm x 51 cm x 21 . 5 cm) through which there was a continuous flow of cold water. The inner tank was incompletely divided by four partitions each 61 in . (16 . 5 cm) long . Two of the compartments thus formed were lined with red and the other two with blue ; the compartments diagonally opposite were of the same colour . Heating lamps were supported above opposite compartments so that either the two red or the two blue ones were heated in the course of each 2-hr experiment . One lamp was switched on for 7 min . When it switched off, the lamp opposite switched on for 7 min . Successive heating of the two like-coloured compartments continued in this way throughout the 2-hr training period . The compartments not heated by lamps were kept cold by the surrounding water. A chick was placed at the centre of the inner tank, with access to all four compartments . Chicks tended to move to the heated compartment, from red to red, or from blue to blue, though some stood shivering in the red compartments when the blue ones were being heated . Control Group Each control chick was placed after test I in a grey cardboard pen similar to that in which chicks were initially reared, and remained in this pen until retested after 2 hr. Chicks in the experimental groups were
Results
Table I. Initial Preferences of Birds in Experiment 1 Red
Blue
No preference
Exposure
35
16
17
Imprinting
30
19
21
Conditioning
41
12
11
Controls
22
13
5
Total
128
60***
54
***Divergence from chance distribution : P<0 .001 (X 2 test) A `shift of preference' score was obtained by subtracting the score on test 1 from the score on test 2 . If the resulting score was negative it was taken as showing a shift of preference towards blue ; if positive, as showing a shift of preference towards red . Thus a shift towards red, for example, might be represented by a change from initial preference for blue to preference for red ; from a strong initial preference for blue to a weaker preference for blue ; from initial preference for blue to no preference ; from no initial preference to a preference for red ; or from a weak initial preference for red to a stronger preference for red . The direction and statistical significance of shifts of preference were examined by means of the Wilcoxon signed-ranks test . Table II shows the changes in preference from test 1 to test 2 for birds in all three experimental groups and for the control birds . In all three experimental groups, differential training produced a significant divergence in preference . Birds trained with red showed a significant shift in preference in the direction of red . Birds trained with blue tended to show increased preference for blue on test 2, but the shift of preference to blue was statistically significant only in the exposure group . In short, all the three training procedures were successful in producing a divergence of
TAYLOR et al. : CHANGING COLOUR PREFERENCES OF CHICKS
5
Table II. Shift in Preference of Birds in Experiment 1 Exposure Shift to R Red-trained
Blue-trained
19
8
Imprinting
Shift to B 4**
20*
Shift to R 24
10
Conditioning
Shift to B
Shift to R
Control
Shift to B
Shift to B
26
7***
5***
18
9
17
(*) 0 . 05
preference, and (apart from the efficiency of exposure to blue in the exposure group) no procedure appeared superior to another in this respect . If control data were ignored, the difference between red-training and blue-training might have suggested that training with an initially `attractive' colour is more effective in changing preference than training with an unattractive colour. However, the control chicks also showed a significant shift towards red on test 2 . Thus the effect, if any, of red-training is unclear ; the effect of blue-training is at least to prevent a shift towards red . Experiment 2 Methods The subjects were 132 cobb chicks, of which 68 were assigned to a 24-hr exposure group, and 64 to a 15-min exposure group . The procedure for testing, `training', and retesting was similar to that of the exposure group in experiment 1 . Chicks were reared individually in a grey pen for 24 hr, then tested in the runway ; after this they were placed in a pen lined with red or with blue, and finally retested in the runway . Chicks in the 24-hr exposure group spent 24 hr in the `exposure' pen with food and water, and were thus retested when 48 hr old ; chicks in the 15min exposure group spent only 15 min in the exposure pen and they were thus still within the `24-hr' age range when retested. Food and water were necessary for survival of the 24-hr group ; water only was given to the 15-min group to provide a similar environment to that of chicks in the exposure group of experiment 1 . Within each experimental group, half the chicks were trained with red, half with blue . Results It will be seen from Table III that the initial preferences (i .e . preference on test l) of birds
Shift to R
(X2
test) for each training
in the 24-hr and 15-min groups do not differ substantially, and do not differ from those obtained from the exposure group in experiment 1. Table IV gives the shifts in preference obtained as a result of training . In both experiments birds trained with red showed a clear shift in preference, on test 2, in the direction of the training colour. The birds `trained' for 24 hr with blue shifted somewhat in preference in the direction of blue ; no similar tendency was apparent in the birds trained for 15 mins . Considered in conjunction with data from experiment 1, these results indicate that the duration of exposure, at any rate to an initially attractive colour, does not affect the magnitude of the shift in preference which results from it ; Table III . Initial Preferences of Birds in Experiment 2 Red
Blue
No preference
24 hr exposure
38
17
14
15 min exposure
23
15
24
Total
61
32**
38
* *Divergence from chance distribution : P<0-005 (X 2 test) Table IV. Shift in Preference of Birds in Experiment 2 24 hr exposure
15 min exposure
Shift to R Shift to B Shift to R Shift to B Red-trained
25
4***
21
Blue-trained
13
19(*)
12
6** 13
(*) P = 0 .07, **P<0 . 005, ***P<0 . 001 (all Wilcoxon T, one tailed) The divergence in direction of shift for birds differentially trained is significant (X2 test) : 24 hr, P<0 . 001 ; 15 min, P<0 . 05 .
6
ANIMAL BEHAVIOUR, 17,
in the case of blue-training there may be a difference in efficiency between 15 min exposure and 2 hr exposure, but no substantial difference between 2 hr and 24 hr (the latter producing rather less evidence of shift than the former) . Since the age of chicks at test 2 varies with the exposure time employed, it is difficult to draw very firm conclusions from these rather slight differences among chicks exposed for 15 min, 2 hr and 24 hr . Experiment 3 Methods 116 cobb chicks served as subjects, 68 of them being assigned to the experimental group and 48 to the control group . For the experimental chicks the procedure was identical to that of the exposure group in experiment 1, except that the colours used were now blue and yellow (ICI Perspex Sheet 250) rather than blue and red . Thus, the chicks were individually reared in grey pens, tested when 24 hr old in a runway with yellow at one end and blue at the other, placed for 2 hr in a pen lined either with yellow or with blue, and retested in the runway . The control chicks were tested similarly but spent the 2 hr between test 1 and test 2 in a grey pen . A chick was assigned a positive score if it was more often observed near the yellow end of the runway during testing, and, as before, a negative score if more time was spent at the blue end . Results Chicks in both groups showed an initial preference for yellow over blue, as seen in Table V .
to the control chicks of experiment 1, showed no shift in preference between test 1 and test 2 . Experiment 4 Methods The subjects employed were 63 Japanese quail chicks, 32 of these in the experimental group and 31 in the control group . For practical convenience the quail chicks were reared in small groups until testing when 4 to 7 days old . The rearing pens were brown in colour and one ft 2 (30 cm 2 ) and were similar to those used for the domestic chicks ; food and water were provided . The quail were tested in the runway with red and blue, behaviour being observed and scored as in previous experiments . Chicks in experimental groups were then placed for 2 hr in a pen lined with red or with blue ; control chicks were placed in a brown pen for the same period, and after this period each chick was retested . Results There is no very clear preference for red over blue on test I (see Table VII) . From Table VIII it will be seen that birds in the experimental group, whether trained with red or with blue, showed a significant shift in preference towards the training colour ; the control chicks showed no consistent shift from test 1 to test 2 . Discussion It is evident that preference of domestic-fowl Table VI. Shift in Preference of Birds in Experiment 3
Blue
No preference
Experimental
35
17
16
Control
26
10
12
61
27***
28
Total ***Divergence test)
from chance
distribution :
P<0 . 001
(X2
Table VI gives the shifts in preference observed in experimental and control groups . The effects in the experimental group were similar to those of experiment 1, but in general less clear-cut ; birds trained with yellow (an initially attractive colour) shifted in preference towards yellow on test 2, while birds trained to blue did not shift in the direction of the training colour . The control chicks, in contrast
Control
Experimental
Table V. Initial Preferences of Domestic Chicks in Experiment 3 Yellow
1
Shift to Y Shift to B Shift to Y Shift to B Yellow-trained
17
Blue-trained
13
7* 19
18
16
*P = 0 .0505 (Wilcoxon T, one-tailed) The divergence of shift in preference for differentially trained birds approaches significance (X2 test) P<0 . 05) Table VII . Initial Preferences of Japanese Quail in Experiment 4 Red
Blue
Experimental
16
12
4
Control
17
9
5
33
21 *
9
Total
No preference
*No significant divergence from chance distribution
TAYLOR et al. : CHANGING COLOUR PREFERENCES OF CHICKS Table VM . Shift in Preference of Quail Chicks in Experiment 4 Experimental
Control
Shift to R Shift to B Shift to R Shift to B Red-trained
13
3**
Blue-trained
3
12**
13
16
**P<0 .005 (Wilcoxon T, one-tailed) The divergence in shift of preference for differentially trained birds is significant beyond 0 . 01 (X2 test) or quail chicks between two colours can be modified in favour of one of these colours by exposure to it. Where the two colours are not initially equally attractive the effects of exposure appear to be asymmetrical ; there is a more marked shift towards the initially preferred colour (as a result of exposure) than towards the non-preferred colour. As far as experiment 1 is concerned, since control chicks as well as redtrained chicks show a clear shift in preference towards red on a second test, it is the behaviour of blue-trained chicks in showing no such shift that provides evidence of the efficacy of training. This might suggest that training with an initially unattractive colour is more effective in modifying preference ; and Taylor et al. (1967) have reported that the texture preferences of domestic chicks appear to be influenced more by exposure to an initially non-preferred texture than by exposure to a preferred texture . However, the results of experiment 3 do not support this conclusion ; in this case a shift towards yellow, the initially preferred colour, occurs only in yellow-trained birds and not in controls, while control and blue-trained chicks are alike in showing no shift . Clearly further studies are need to clarify the interpretation of our findings. It appears that the asymmetry in the effects of training is to be attributed to the differential attractiveness of the colours used ; the Japanese quail chicks, which exhibited no clear initial preference for one colour over the other, showed a clear shift of preference in the direction of the `exposure' colour, whether this was red or blue. From consideration of experiments 1 and 2 together it appears that the effect of exposure is not dependent upon the exposure time allowed ; there is virtually no difference in the magnitude of the shifts brought about by 15 min, 2 hr or 24 hr exposure . There are of course other variables confounded with that of exposure time, for
7
example age of the chicks at test 2, the time elapsing between tests, the presence of food and water during 24 hr exposure and of water alone during 15 min or 2 hr exposure. Hence, while these variables do not a priori suggest effects which might systematically obscure some effect of exposure time, we cannot state with certainty that the duration of exposure (above some minimum time which is briefer than any we have used) is unimportant for the modification of preference . It may well be, for example, that the shift of preference brought about by a longer exposure time, if not greater in extent, may be better retained. We are at present investigating the effect of varying exposure time upon the retention of preferences acquired through exposure. Finally, the results of experiment 1 show that no one training procedure of the three used -exposure, imprinting, or conditioningemerges as superior to the rest ; all are similar in their effects. How these procedures are related to one another may be described in a number of ways. It could be argued that our exposure training is a form of imprinting ; imprinting has been shown to occur to stationary as well as to moving objects (e.g . Abercrombie & James, 1961), and exposure training resembles classical imprinting in procedure more closely than it resembles classical or instrumental conditioning . It is then interesting to note that imprinting procedures, commonly held to be independent of conventional reward, are as effective in modifying behaviour as is a conditioning procedure which systematically rewards selection of one stimulus value rather than another . A second view relating these procedures might be that all are essentially reward learning ; since water was present in exposure and imprinting pens, drinking might be held to have reinforced proximity to the colour predominant in the pen. If this interpretation is accepted then it is curious that 24 hr exposure with food as well as water did not produce clearer evidence of shift than, say, 2 hr exposure with water alone ; and, again, that the more systematic and discriminative reinforcement of the conditioning procedure did not prove superior in modifying performance . We are not specifically concerned to deny the importance of conventional reward in exposure and imprinting procedures, although there is evidence that the presence or absence of water in the training pen does not affect the efficiency of imprinting (Taylor & Sluckin, 1964) . There is however a
8
ANIMAL BEHAVIOUR, 17,
final basis for comparison of our training procedures . All have in common that they bring the animal into proximity with one colour rather than another, whether this end is achieved by confinement in a coloured pen, by imprinting to a moving coloured object, or by coupling a colour with heat . It might be argued that the development or modification of preference is attained by exposure to a given colour or other characteristic, and that all our procedures are effective in so far as they control the proximity of chick and colour . Thus, `reinforcement training' might be regarded as the vehicle for exposure learning, rather than the reverse . Clearly, however, such a conclusion, while suggested by our findings, would have to rely on weightier evidence . Summary Domestic fowl and Japanese quail chicks were first tested individually for approach choice between two colours, and, after some experience of one or the other colour or neither, were again tested for choice between the same colours . In two experiments domestic chicks were given as `training' experience 2 hr of exposure to coloured walls of a pen, or 2 hr conventional imprinting to a coloured object, or 2 hr conditioning in which heat was used as UCS and colour as CS. All methods were found to be effective in influencing the chicks' preference . In another experiment, using the exposure method only and different durations of exposure, it was found that 15 min was not much less effective than 24 hr in modifying the chicks'
1
colour choices . In a further experiment quail chicks were used ; although their initial preferences were not quite like those of domestic chicks, these preferences were at least as readily modifiable . REFERENCES Abercrombie, B . & James, H. (1961) . The stability of the domestic chick's response to visual flicker . Anim . Behav., 9, 205-212 . Gray, P . H . (1961) . The releasers of imprinting : differential reactions to color as a function of maturation. J. comp . physio!. Psycho!., 54, 597-601 . Kear, J. (1964) . Colour preference in young anatidae . Ibis, 106, 361-369. Kear, J . (966) . The pecking response of young Coots Falica atra and Moorhens Gallinula chloropus. Ibis, 108, 118-122 . Lashley, K . S. (1916) . Color vision in birds . I . The spectrum of the domestic fowl . J. Anim. Behav ., 6, 1-26. Schaefer, H . H . & Hess, E. H . (1959) . Color preferences in imprinting objects . Z. Tierpsychol., 16,161-172. Smith, F . V . & Hoyes, P . A . (1961) . Properties of the visual stimuli for the approach response in the domestic chick . Anim . Behav., 9, 159-166 . Smith, T. L . & Meyer, M . E . (1965) . Preference of chicks in the original stimulus situation of imprinting . Psychonom . Sci., 2, 121-122 . Taylor, A ., Sluckin, W ., Hewitt, R . & Guiton, P . (1967). The formation of attachments by domestic chicks in two textures. Anim . Behav., 15, 512-517 . Taylor, K. F. & Sluckin, W . (1964) . Flocking of domestic chicks . Nature, Lond., 201, 108-109 . Thorndike, E . L . (1911) . Animal Intelligence . New York : Macmillan . Weidmann, U . (1965) . `Colour preference' and pecking response of young Moorhens Gallinula chloropus and Coots Fulica atra . Ibis, 107, 108-110 . (Received 7 September 1967 ; revised 14 February 1968 ; Ms . number : 773)
CHANGING COLOUR PREFERENCES OF CHICKS BY
ANN TAYLOR, W . SLUCKIN & ROSEMARY HEWITT Department of Psychology, University of Leicester
Young nidifugous birds readily show preferences for some colours over others . Thorndike (1911) observed domestic chicks pecking coloured spots, and Lashley (1916) studied the chick's approach responses to coloured surfaces . More recently, chicks' preferences for colours were investigated by Schaefer & Hess (1959), by Smith & Hoyes (1961), and by Smith & Meyer (1965) . Kear (1964) tested pecking preferences for colours in the young of many species of Anatidae and Phasianidae, and Weidmann (1965) similarly reported on young moorhens and coots . Findings of all these workers have been dependent not only on the methods of testing but also on the characteristics of the various colours used and especially on their luminosity (Kear, 1966) . Very few attempts have been made to study changes in preference rather than colour preferences as such . Gray (1961) attempted to study colour preferences of domestic fowl chicks as a function of maturation ; he reported that choices, as measured by approach responses, tended to change with age . Our own interest has been in the stability or otherwise of colour preferences in relation to various types of intervening experience . In our experiments we used as subjects domestic fowl and Japanese quail chicks . We tested them individually for approach preference between two given colours, and then tested each bird again in the same way after `training' of some kind with one or the other colour or after no training. Four experiments are reported . Experiment I is concerned with the efficacy of different methods of altering the domestic chicks' colour preferences . As `training' methods we used (a) exposure to coloured walls of rearing pens, (b) conventional imprinting and (c) a form of conditioning with heat as the unconditioned stimulus (UCS) . Experiment 2 is concerned with the variable of duration of experience, using only one method of effecting a shift of preference, namely the `exposure' procedure . Experiments 3 and 4 attempt to shed some light on the generality of the effects we have found . To this end we used a new pair of colours, and also experimented with a further species, the Japanese quail .
Experiment 1 Methods The subjects were 242 chicks hatched from `cobb' eggs in the laboratory ; 68 were assigned to the exposure group, 70 to the imprinting group, 64 to the conditioning and 40 to a control group . Each chick was moved from the incubator into a grey cardboard pen, 1 ft x 1 ft x 1 ft (30 cm 3), open at the top and heated by a 60 W radiant-heat bulb . A chick in the pen was visually isolated from other chicks, although it could hear them . Food and water were provided in each cage . After 24 hr each chick was removed from its pen and placed in a runway 22 in . (56 cm) long, 6 in . (15 cm) wide and 8 in . (20 cm) high . The floor was marked off in 1-in . (2 . 5 cm) strips ; the central line was labelled 0 and the lines to either side of it were numbered 1 to 11, line 1I coinciding with the end of the runway . Clipped to each end of the runway was a 6 in . (15 cm) square of coloured plastic ; one end was blue (Oroglass, Blue 2326, „ in . (3 mm) thick . and the other red (ICI Perspex Sheet 461) . All the coloured plastic used in these experiments was rubbed down with sand paper to minimize reflection . A light bulb was suspended directly above each end of the runway. A chick was placed in the runway on the zero line and facing a long side ; a stopwatch was started and the chick was observed on every minute for 5 min, and its position noted . If the chick was between lines 6 and 11 towards the red end of the runway, it was given a score of -{-1 ; if it was between lines 6 and I 1 towards the blue end, a score of -1 ; otherwise it received a score of 0 . Thus the total scores during the 5-min test ranged from +5 to -5 . A positive score was taken to indicate a perference for red, and a negative score a preference for blue . After this test the chick was removed from the runway for 2 hr, during which time it received the experimental or control treatment to which it had been assigned . At the end of 2 hr it was replaced in the runway and tested, and its behaviour scored, as before . For half the chicks in each group red was on the right of the entry point and blue on the left ; for the rest the positions were reversed . The colours for any
4
ANIMAL BEHAVIOUR, 17, 1
one chick were in the same position in both the pre-training and the post-training tests . Experimental procedures were as follows :
assigned alternately to red-training and bluetraining, not on the basis of their initial score .
(a) Exposure. After test 1 the chick was placed in a pen, 1 ft x 1 ft x 1 ft (30 cm 3), three sides of which were lined either with red or with blue Perspex. Water was available in the pen . Half the chicks were exposed to red in this way and half were exposed to blue .
It will be seen from Table I that a clear preference emerged on test 1 for red over blue, chicks in all groups showing essentially the same pattern . In no case were the proportions of redpreferring, blue-preferring and non-preferring birds different for red-training and blue-training groups .
(b) Imprinting . The chick was placed, after test 1, in a grey circular pen 18 in . (46 cm) in diameter and 12 in . (30 cm) high in which water was available . In the centre of the pen was a small synchronous motor driving a cam which switched on another synchronous motor for 21 sec and off for 31 sec. This motor caused a 2-in . (5 cm) square of Perspex (red or blue) to move round the pen at a height of I in . (2 . 5 cm) from the ground . The chick was given 2 hr inside the pen with the moving object . As expected, some chicks followed the Perspex square . (c) Conditioning. The conditioning apparatus consisted of one tank 18 in . x 18 in . x 81 in . (46 cm x 46 cm x 21 . 5 cm) inside another tank 20 in . x 20 in . x 81 in . (51 cm x 51 cm x 21 . 5 cm) through which there was a continuous flow of cold water. The inner tank was incompletely divided by four partitions each 61 in . (16 . 5 cm) long . Two of the compartments thus formed were lined with red and the other two with blue ; the compartments diagonally opposite were of the same colour . Heating lamps were supported above opposite compartments so that either the two red or the two blue ones were heated in the course of each 2-hr experiment . One lamp was switched on for 7 min . When it switched off, the lamp opposite switched on for 7 min . Successive heating of the two like-coloured compartments continued in this way throughout the 2-hr training period . The compartments not heated by lamps were kept cold by the surrounding water. A chick was placed at the centre of the inner tank, with access to all four compartments . Chicks tended to move to the heated compartment, from red to red, or from blue to blue, though some stood shivering in the red compartments when the blue ones were being heated . Control Group Each control chick was placed after test I in a grey cardboard pen similar to that in which chicks were initially reared, and remained in this pen until retested after 2 hr. Chicks in the experimental groups were
Results
Table I. Initial Preferences of Birds in Experiment 1 Red
Blue
No preference
Exposure
35
16
17
Imprinting
30
19
21
Conditioning
41
12
11
Controls
22
13
5
Total
128
60***
54
***Divergence from chance distribution : P<0 .001 (X 2 test) A `shift of preference' score was obtained by subtracting the score on test 1 from the score on test 2 . If the resulting score was negative it was taken as showing a shift of preference towards blue ; if positive, as showing a shift of preference towards red . Thus a shift towards red, for example, might be represented by a change from initial preference for blue to preference for red ; from a strong initial preference for blue to a weaker preference for blue ; from initial preference for blue to no preference ; from no initial preference to a preference for red ; or from a weak initial preference for red to a stronger preference for red . The direction and statistical significance of shifts of preference were examined by means of the Wilcoxon signed-ranks test . Table II shows the changes in preference from test 1 to test 2 for birds in all three experimental groups and for the control birds . In all three experimental groups, differential training produced a significant divergence in preference . Birds trained with red showed a significant shift in preference in the direction of red . Birds trained with blue tended to show increased preference for blue on test 2, but the shift of preference to blue was statistically significant only in the exposure group . In short, all the three training procedures were successful in producing a divergence of
TAYLOR et al. : CHANGING COLOUR PREFERENCES OF CHICKS
5
Table II. Shift in Preference of Birds in Experiment 1 Exposure Shift to R Red-trained
Blue-trained
19
8
Imprinting
Shift to B 4**
20*
Shift to R 24
10
Conditioning
Shift to B
Shift to R
Control
Shift to B
Shift to B
26
7***
5***
18
9
17
(*) 0 . 05
preference, and (apart from the efficiency of exposure to blue in the exposure group) no procedure appeared superior to another in this respect . If control data were ignored, the difference between red-training and blue-training might have suggested that training with an initially `attractive' colour is more effective in changing preference than training with an unattractive colour. However, the control chicks also showed a significant shift towards red on test 2 . Thus the effect, if any, of red-training is unclear ; the effect of blue-training is at least to prevent a shift towards red . Experiment 2 Methods The subjects were 132 cobb chicks, of which 68 were assigned to a 24-hr exposure group, and 64 to a 15-min exposure group . The procedure for testing, `training', and retesting was similar to that of the exposure group in experiment 1 . Chicks were reared individually in a grey pen for 24 hr, then tested in the runway ; after this they were placed in a pen lined with red or with blue, and finally retested in the runway . Chicks in the 24-hr exposure group spent 24 hr in the `exposure' pen with food and water, and were thus retested when 48 hr old ; chicks in the 15min exposure group spent only 15 min in the exposure pen and they were thus still within the `24-hr' age range when retested. Food and water were necessary for survival of the 24-hr group ; water only was given to the 15-min group to provide a similar environment to that of chicks in the exposure group of experiment 1 . Within each experimental group, half the chicks were trained with red, half with blue . Results It will be seen from Table III that the initial preferences (i .e . preference on test l) of birds
Shift to R
(X2
test) for each training
in the 24-hr and 15-min groups do not differ substantially, and do not differ from those obtained from the exposure group in experiment 1. Table IV gives the shifts in preference obtained as a result of training . In both experiments birds trained with red showed a clear shift in preference, on test 2, in the direction of the training colour. The birds `trained' for 24 hr with blue shifted somewhat in preference in the direction of blue ; no similar tendency was apparent in the birds trained for 15 mins . Considered in conjunction with data from experiment 1, these results indicate that the duration of exposure, at any rate to an initially attractive colour, does not affect the magnitude of the shift in preference which results from it ; Table III . Initial Preferences of Birds in Experiment 2 Red
Blue
No preference
24 hr exposure
38
17
14
15 min exposure
23
15
24
Total
61
32**
38
* *Divergence from chance distribution : P<0-005 (X 2 test) Table IV. Shift in Preference of Birds in Experiment 2 24 hr exposure
15 min exposure
Shift to R Shift to B Shift to R Shift to B Red-trained
25
4***
21
Blue-trained
13
19(*)
12
6** 13
(*) P = 0 .07, **P<0 . 005, ***P<0 . 001 (all Wilcoxon T, one tailed) The divergence in direction of shift for birds differentially trained is significant (X2 test) : 24 hr, P<0 . 001 ; 15 min, P<0 . 05 .
6
ANIMAL BEHAVIOUR, 17,
in the case of blue-training there may be a difference in efficiency between 15 min exposure and 2 hr exposure, but no substantial difference between 2 hr and 24 hr (the latter producing rather less evidence of shift than the former) . Since the age of chicks at test 2 varies with the exposure time employed, it is difficult to draw very firm conclusions from these rather slight differences among chicks exposed for 15 min, 2 hr and 24 hr . Experiment 3 Methods 116 cobb chicks served as subjects, 68 of them being assigned to the experimental group and 48 to the control group . For the experimental chicks the procedure was identical to that of the exposure group in experiment 1, except that the colours used were now blue and yellow (ICI Perspex Sheet 250) rather than blue and red . Thus, the chicks were individually reared in grey pens, tested when 24 hr old in a runway with yellow at one end and blue at the other, placed for 2 hr in a pen lined either with yellow or with blue, and retested in the runway . The control chicks were tested similarly but spent the 2 hr between test 1 and test 2 in a grey pen . A chick was assigned a positive score if it was more often observed near the yellow end of the runway during testing, and, as before, a negative score if more time was spent at the blue end . Results Chicks in both groups showed an initial preference for yellow over blue, as seen in Table V .
to the control chicks of experiment 1, showed no shift in preference between test 1 and test 2 . Experiment 4 Methods The subjects employed were 63 Japanese quail chicks, 32 of these in the experimental group and 31 in the control group . For practical convenience the quail chicks were reared in small groups until testing when 4 to 7 days old . The rearing pens were brown in colour and one ft 2 (30 cm 2 ) and were similar to those used for the domestic chicks ; food and water were provided . The quail were tested in the runway with red and blue, behaviour being observed and scored as in previous experiments . Chicks in experimental groups were then placed for 2 hr in a pen lined with red or with blue ; control chicks were placed in a brown pen for the same period, and after this period each chick was retested . Results There is no very clear preference for red over blue on test I (see Table VII) . From Table VIII it will be seen that birds in the experimental group, whether trained with red or with blue, showed a significant shift in preference towards the training colour ; the control chicks showed no consistent shift from test 1 to test 2 . Discussion It is evident that preference of domestic-fowl Table VI. Shift in Preference of Birds in Experiment 3
Blue
No preference
Experimental
35
17
16
Control
26
10
12
61
27***
28
Total ***Divergence test)
from chance
distribution :
P<0 . 001
(X2
Table VI gives the shifts in preference observed in experimental and control groups . The effects in the experimental group were similar to those of experiment 1, but in general less clear-cut ; birds trained with yellow (an initially attractive colour) shifted in preference towards yellow on test 2, while birds trained to blue did not shift in the direction of the training colour . The control chicks, in contrast
Control
Experimental
Table V. Initial Preferences of Domestic Chicks in Experiment 3 Yellow
1
Shift to Y Shift to B Shift to Y Shift to B Yellow-trained
17
Blue-trained
13
7* 19
18
16
*P = 0 .0505 (Wilcoxon T, one-tailed) The divergence of shift in preference for differentially trained birds approaches significance (X2 test) P<0 . 05) Table VII . Initial Preferences of Japanese Quail in Experiment 4 Red
Blue
Experimental
16
12
4
Control
17
9
5
33
21 *
9
Total
No preference
*No significant divergence from chance distribution
TAYLOR et al. : CHANGING COLOUR PREFERENCES OF CHICKS Table VM . Shift in Preference of Quail Chicks in Experiment 4 Experimental
Control
Shift to R Shift to B Shift to R Shift to B Red-trained
13
3**
Blue-trained
3
12**
13
16
**P<0 .005 (Wilcoxon T, one-tailed) The divergence in shift of preference for differentially trained birds is significant beyond 0 . 01 (X2 test) or quail chicks between two colours can be modified in favour of one of these colours by exposure to it. Where the two colours are not initially equally attractive the effects of exposure appear to be asymmetrical ; there is a more marked shift towards the initially preferred colour (as a result of exposure) than towards the non-preferred colour. As far as experiment 1 is concerned, since control chicks as well as redtrained chicks show a clear shift in preference towards red on a second test, it is the behaviour of blue-trained chicks in showing no such shift that provides evidence of the efficacy of training. This might suggest that training with an initially unattractive colour is more effective in modifying preference ; and Taylor et al. (1967) have reported that the texture preferences of domestic chicks appear to be influenced more by exposure to an initially non-preferred texture than by exposure to a preferred texture . However, the results of experiment 3 do not support this conclusion ; in this case a shift towards yellow, the initially preferred colour, occurs only in yellow-trained birds and not in controls, while control and blue-trained chicks are alike in showing no shift . Clearly further studies are need to clarify the interpretation of our findings. It appears that the asymmetry in the effects of training is to be attributed to the differential attractiveness of the colours used ; the Japanese quail chicks, which exhibited no clear initial preference for one colour over the other, showed a clear shift of preference in the direction of the `exposure' colour, whether this was red or blue. From consideration of experiments 1 and 2 together it appears that the effect of exposure is not dependent upon the exposure time allowed ; there is virtually no difference in the magnitude of the shifts brought about by 15 min, 2 hr or 24 hr exposure . There are of course other variables confounded with that of exposure time, for
7
example age of the chicks at test 2, the time elapsing between tests, the presence of food and water during 24 hr exposure and of water alone during 15 min or 2 hr exposure. Hence, while these variables do not a priori suggest effects which might systematically obscure some effect of exposure time, we cannot state with certainty that the duration of exposure (above some minimum time which is briefer than any we have used) is unimportant for the modification of preference . It may well be, for example, that the shift of preference brought about by a longer exposure time, if not greater in extent, may be better retained. We are at present investigating the effect of varying exposure time upon the retention of preferences acquired through exposure. Finally, the results of experiment 1 show that no one training procedure of the three used -exposure, imprinting, or conditioningemerges as superior to the rest ; all are similar in their effects. How these procedures are related to one another may be described in a number of ways. It could be argued that our exposure training is a form of imprinting ; imprinting has been shown to occur to stationary as well as to moving objects (e.g . Abercrombie & James, 1961), and exposure training resembles classical imprinting in procedure more closely than it resembles classical or instrumental conditioning . It is then interesting to note that imprinting procedures, commonly held to be independent of conventional reward, are as effective in modifying behaviour as is a conditioning procedure which systematically rewards selection of one stimulus value rather than another . A second view relating these procedures might be that all are essentially reward learning ; since water was present in exposure and imprinting pens, drinking might be held to have reinforced proximity to the colour predominant in the pen. If this interpretation is accepted then it is curious that 24 hr exposure with food as well as water did not produce clearer evidence of shift than, say, 2 hr exposure with water alone ; and, again, that the more systematic and discriminative reinforcement of the conditioning procedure did not prove superior in modifying performance . We are not specifically concerned to deny the importance of conventional reward in exposure and imprinting procedures, although there is evidence that the presence or absence of water in the training pen does not affect the efficiency of imprinting (Taylor & Sluckin, 1964) . There is however a
8
ANIMAL BEHAVIOUR, 17,
final basis for comparison of our training procedures . All have in common that they bring the animal into proximity with one colour rather than another, whether this end is achieved by confinement in a coloured pen, by imprinting to a moving coloured object, or by coupling a colour with heat . It might be argued that the development or modification of preference is attained by exposure to a given colour or other characteristic, and that all our procedures are effective in so far as they control the proximity of chick and colour . Thus, `reinforcement training' might be regarded as the vehicle for exposure learning, rather than the reverse . Clearly, however, such a conclusion, while suggested by our findings, would have to rely on weightier evidence . Summary Domestic fowl and Japanese quail chicks were first tested individually for approach choice between two colours, and, after some experience of one or the other colour or neither, were again tested for choice between the same colours . In two experiments domestic chicks were given as `training' experience 2 hr of exposure to coloured walls of a pen, or 2 hr conventional imprinting to a coloured object, or 2 hr conditioning in which heat was used as UCS and colour as CS. All methods were found to be effective in influencing the chicks' preference . In another experiment, using the exposure method only and different durations of exposure, it was found that 15 min was not much less effective than 24 hr in modifying the chicks'
1
colour choices . In a further experiment quail chicks were used ; although their initial preferences were not quite like those of domestic chicks, these preferences were at least as readily modifiable . REFERENCES Abercrombie, B . & James, H. (1961) . The stability of the domestic chick's response to visual flicker . Anim . Behav., 9, 205-212 . Gray, P . H . (1961) . The releasers of imprinting : differential reactions to color as a function of maturation. J. comp . physio!. Psycho!., 54, 597-601 . Kear, J. (1964) . Colour preference in young anatidae . Ibis, 106, 361-369. Kear, J . (966) . The pecking response of young Coots Falica atra and Moorhens Gallinula chloropus. Ibis, 108, 118-122 . Lashley, K . S. (1916) . Color vision in birds . I . The spectrum of the domestic fowl . J. Anim. Behav ., 6, 1-26. Schaefer, H . H . & Hess, E. H . (1959) . Color preferences in imprinting objects . Z. Tierpsychol., 16,161-172. Smith, F . V . & Hoyes, P . A . (1961) . Properties of the visual stimuli for the approach response in the domestic chick . Anim . Behav., 9, 159-166 . Smith, T. L . & Meyer, M . E . (1965) . Preference of chicks in the original stimulus situation of imprinting . Psychonom . Sci., 2, 121-122 . Taylor, A ., Sluckin, W ., Hewitt, R . & Guiton, P . (1967). The formation of attachments by domestic chicks in two textures. Anim . Behav., 15, 512-517 . Taylor, K. F. & Sluckin, W . (1964) . Flocking of domestic chicks . Nature, Lond., 201, 108-109 . Thorndike, E . L . (1911) . Animal Intelligence . New York : Macmillan . Weidmann, U . (1965) . `Colour preference' and pecking response of young Moorhens Gallinula chloropus and Coots Fulica atra . Ibis, 107, 108-110 . (Received 7 September 1967 ; revised 14 February 1968 ; Ms . number : 773)