Ž . Ž .
Fig. 2. a The latencies to peck at and b the numbers of pecks delivered at each of the coloured string devices when these were presented simultaneously for 10 min on each of 5 consecutive days in Experiment 2.
means, with their standard errors, were 367.0 43.0, 205.1 35.4, 83.2 21.0, 35.0 16.0 and 32.1 15.4 for days 1 through 5, respectively. Analysis of deviance revealed
Ž
2
. that the numbers of pecks at the stimuli x s 78.74, df s 4, P - 0.001 and of pecking
Ž
2
. bouts x s 63.57, df s 4 , P - 0.001 increased markedly with repeated exposure and
that the white and yellow strings consistently attracted more pecking than the red, blue Ž
2 2
or green bunches x s 46.64, df s 4, P - 0.001 and x s 52.79, df s 4, P - 0.001
. for pecks and bouts, respectively . There were no significant interactions between colour
Ž
2
. and repeated presentation for the numbers of pecks
x s 1.22, df s 4, P 0.05 or Ž
2
. pecking bouts x s 0.95, df s 4, P 0.05 . The latencies to peck and the numbers of
pecks directed at each of the coloured stimuli on each of the 5 days are shown in the purely descriptive Fig. 2a and b, respectively.
The present findings clearly demonstrate that white or yellow string elicited substan- tially more pecking than did the other devices. Indeed, the chicks showed comparatively
Ž .
little interest in red, blue or green string see General Discussion . Like Experiment 1, there was no evidence of habituation here; rather the stimuli attracted progressively
more interest with repeated exposure. The practical implications of these results and their relevance to the continuing debate over colour preferences are discussed in greater
detail below.
5. Experiment 3: effects of varying colours and complexity
Complexity of the environment and of its component features is thought to be an important variable underpinning some of the beneficial effects of enrichment. For
example, it has been suggested that increasing the range of stimuli to which animals are Ž
. exposed is ‘‘healthier’’ Fox, 1986; Renner and Rosenzweig, 1987 and less ‘‘boring’’
Ž .
Wemelsfelder, 1985 , that structural, visual and textural complexity encourages interac- Ž
tion between the animal and its environment Dember et al., 1957; McGrew et al., 1986;
. Chamove, 1989 , and that environmental complexity reduces distress in captive animals
Ž .
Snyder, 1975 . White and yellow were identified as the most attractive colours in Experiment 2. A
combination of white, yellow and green string also readily attracted pecking by ISA Ž
. Brown chicks Jones and Carmichael, 1999a but we did not compare chicks’ interest in
multi-coloured stimuli versus monochromatic ones in that study. In the present experi- ment, we asked if combining colours and, hence, arguably increasing complexity would
increase interest in the devices. We compared pecking at bunches of only white or only yellow string with that at combinations of white and yellow strings or of all the five
Ž .
colours tested above white, yellow, green, red, blue . 5.1. Methods
The partitions were removed from the wooden boxes described above so that each Ž
. one provided an area measuring 72 = 38 = 30 cm length = breadth = height . Thirty-six
1-day-old females were housed in pairs in 18 of these boxes. Husbandry and mainte- nance procedures were similar to those described previously and the birds remained
undisturbed until testing began at 5 days of age.
Ž . Ž
. Four test stimuli were used here. These were either: a five strands of white W
Ž . Ž .
Ž . polypropylene twine, b five yellow Y strands, c three white and two yellow
Ž .
Ž W q Y or two white and three yellow strands the two combinations were equally
. Ž .
represented , and d one strand each of white, yellow, green, red and blue twine Ž
. multi-coloured, M-C . All the strands were 8 cm long and they were bound together at
one end with clear tape. At test, all four stimuli were presented simultaneously for 10 min on each of 5 consecutive days at approximately equi-distant positions, two on one
of the 72-cm walls and one on each of the 38-cm ones. The position of each stimulus varied across days according to a quasi-random design so that each one was presented in
all four positions at least once. The chicks’ responses were recorded onto videotape and we subsequently measured the latencies to peck as well as the numbers of pecks and
pecking bouts that were directed at each stimulus. The data were analysed using the same statistical methods as those described in Experiment 2.
5.2. Results and discussion The chicks pecked sooner at the white string than at any of the other devices; this
Ž .
stimulus also elicited more pecks and pecking bouts Table 3, and below . The chicks’ preferences were almost invariably W Y W q Y M-C. Unlike the conservatism
shown by chicks in the previous experiment, those tested here did not show consistency Ž
2
in the order in which they pecked the stimuli across test days x s 52.71, df s 54,
. P 0.05 . Similarly, significant agreement across chicks and within days in the order of
Ž
2
. pecking at each stimulus was only achieved on days 1
x s 14.04, df s 3, P - 0.01 Ž
2
. and 3
x s 9.18, df s 3, P - 0.05 . However, this relative lack of consistency may have reflected the high numbers of ties and of maximum latencies in the present data set.
Furthermore, shifts in the chicks’ preferences were almost invariably between the W, Y or W q Y stimuli. Indeed, upon pooling the data from each test day we found a
Table 3 Ž
. The latencies to peck and the numbers of pecks and pecking bouts meansqstandard errors at white, yellow,
whiteqyellow or multi-coloured bunches of string averaged across all 5 test days and the results of Friedman Ž
. two-way analyses of variance df s 3
Measure String stimuli
S P
White Yellow
WhiteqYellow Multi-coloured
Ž . Lat. peck s
445.334.8 501.223.6
488.627.0 554.817.4
17.53 -
0.001 Ž
. Pecks no
1.960.78 1.560.71
0.640.20 0.200.10
19.76 -
0.001 Ž
. Pecking bouts no
1.170.36 0.810.28
0.500.15 0.160.07
20.59 -
0.001 Ž .
Ž .
df sdegrees of freedom; Lat. peck s latency to peck; s sseconds; no s number
significant difference between the numbers of times each stimulus was the first to be Ž
2
. Ž
. Ž
. pecked
x s 14.47, df s 3, P - 0.01 ; this followed the pattern of W 20 , Y 11 , Ž
. Ž .
W q Y 12 and M-C 2 . Collectively, the latencies to peck at any of the stimuli, regardless of their nature, fell
Ž .
significantly H s 12.30, df s 4, P - 0.02 with repeated exposure; the cumulative
Ž .
means all stimuli pooled and their SEMs were 495.8 47.4, 437.7 53.3, 355.7 62.5, 263.3 60.1 and 254.4 66.7 for days 1 through 5, respectively. Analysis of
Ž deviance also revealed that the stimuli attracted progressively more pecks Fig. 3b;
2
. Ž
2
. x s 39.43, df s 43, P - 0.001 and pecking bouts
x s 19.78, df s 4, P - 0.001 upon repeated presentation and that W or Y strings were generally more attractive than
the W q Y or the M-C ones, particularly on days 4 and 5. There were no detectable interactions between stimulus type and day of testing. The descriptive patterns of
responses to each of the stimuli are shown in Fig. 3a and b.
The chicks showed less pecking at any of these devices here than they did in our other experiments; this likely reflects a batch effect. Despite this, the present findings
are consistent with previous ones that bunches of white or yellow strings are particularly attractive and that the pecking devices elicited progressively more interest with repeated
Ž .
exposure Experiment 2, Jones and Carmichael, 1998; 1999a . Furthermore, the differ-
Ž . Ž .
Ž .
Fig. 3. a The latencies to peck at and b the numbers of pecks delivered at each of the white W , yellow Ž .
Ž .
Ž .
Y , white plus yellow WqY or multi-coloured M-C string devices when these were presented simultane- ously for 10 min on each of the test days in Experiment 3.
ences between the chicks’ responses to the various stimuli became more pronounced with repeated exposure. Our present observation that the multi-coloured stimulus elicited
by far the least pecking throughout this experiment could be interpreted in at least three ways. Firstly, it may simply not have been sufficiently attractive. Secondly, the chicks
may have perceived one or more of the colours andror the increased complexity of the stimulus to be frightening or otherwise aversive. Thirdly, chicks may just prefer simple
stimuli to more complex ones.
6. Experiment 4: effects of varying the size of the string
