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
The size as well as the colour or shape of an object can influence the pecking Ž
. responses of young chicks Rogers, 1995 . It could be argued that bigger stimuli would
be more conspicuous and might thereby attract more attention and interest than smaller ones. On the other hand, large stimuli might be perceived as threatening by small chicks.
The present experiment addressed this issue by presenting chicks with a number of white string devices differing in size.
6.1. Methods Thirty-six female chicks were obtained at one day of age and housed in pairs in 18 of
the 38 = 36 = 30 cm wooden boxes under the conditions previously described. Four bunches of white string differing in length and width were introduced simultaneously
Ž . into the home cage when the chicks were 5 days old. The devices consisted of: a four
Ž . Ž .
strands each measuring 4 cm in length, b four strands of 8-cm length, c eight strands Ž .
of 4 cm length and, d eight strands of 8 cm length. The first two devices were approximately 1.2 cm wide whereas the other two were 2.4 cm wide. They were
suspended from the tops of three of the four walls. The chicks’ responses were recorded onto videotape using an overhead micro camera during each 10-min observation period.
This procedure was repeated on 4 consecutive days and the position of each stimulus was rotated daily to ensure that it was presented once at each of the four locations.
During subsequent analysis of the videotapes, we measured the latencies to peck each of the four stimuli as well as the numbers of pecks and pecking bouts that each one
received. The results were examined using the same analyses as those described in Experiment 2.
6.2. Results and discussion Ž
. Using pooled results from all 4 test days we found no significant differences in the
Ž .
Ž latencies to peck S s 1.26, df s 3, P s 0.739 or in the numbers of pecks S s 0.18,
. Ž
. df s 3, P s 0.981 or pecking bouts S s 1.97, df s 3, P s 0.579 directed at any of the
Ž .
stimuli Table 4 . There was no detectable evidence of consistency in the order in which the stimuli were pecked either within or across test days. Neither was there a significant
difference between the numbers of times each stimulus was the first to be pecked; these were 17, 19, 15 and 16 for devices a, b, c and d, respectively.
Table 4 Meansstandard errors of the latencies to peck and the numbers of pecks and pecking bouts, averaged across
all 5 test days, directed at white string devices differing in size Ž
. Measure
Number and length cm of strings 4=4
4=8 8=4
8=8 Ž .
Lat. peck s 374.425.0
397.031.4 406.429.5
414.527.2 Ž
. Pecks no
2.030.43 3.011.00
3.171.10 3.060.98
Ž .
Pecking bouts no 1.320.21
1.470.35 1.330.29
1.360.29 Ž
. Ž .
Ž .
cm s centimetres; Lat. peck s latency to peck; s sseconds; no s number
Although the latency to the first peck, regardless of stimulus, fell from 150.8 41.4 Ž
on day 1 to 131.3 52.9 s on day 4, this trend was not significant H s 5.87, df s 3, .
P s 0.12 . Analysis of deviance also revealed that there were no effects of stimulus type Ž
2 2
or repeated exposure on the numbers of pecks x s 1.47, df s 3, P 0.80; x s 3.99, .
Ž
2 2
df s 3, P 0.30 or pecking bouts x s 0.10, df s 3, P 0.99; x s 2.80 df s 3,
. Ž
2
P 0.30 , neither were there any significant interactions x s 4.25, df s 9, P 0.80;
2
. x s 3.20, df s 9, P 0.98 .
Clearly, varying the size of the stimulus exerted no detectable effects on the chicks’ pecking responses. This finding suggests that the size of the pecking device is not an
influential factor, at least within the confines of the dimensions used here. Unlike the Ž
previous experiments in this study and those reported elsewhere Jones and Carmichael, .
1998, 1999a there was no evidence of increasing interest with repeated exposure here. However, neither was there any evidence of habituation.
7. Experiment 5: effects of combining string and beads
