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
The effects of combining stimuli were further assessed in the present experiment but, unlike Experiment 3, we combined different types of putatively attractive stimuli here
rather than incorporating different features of the same stimulus in one device. We have already shown that white string is a potent pecking stimulus and, though matte white
beads elicited less pecking than string in Experiment 1, chicks are thought to have a
Ž .
propensity to peck at small spherical objects Dawkins, 1968; Rogers, 1995 . Further- more, shiny stimuli are thought to be not only attractive but perhaps even supernormal
Ž .
Rheingold and Hess, 1957 . Therefore, in the present experiment we examined the effects of incorporating small shiny bead rings in the white string devices.
7.1. Methods Fifty six female chicks were obtained at 1 day of age and housed in pairs under the
same conditions in the 38 = 36 = 30 cm wooden boxes previously described. Two test stimuli were introduced simultaneously into the home cage when the chicks were 5 days
Ž . old. The stimuli consisted of: a eight strands of 8-cm long, white polypropylene twine
Ž . tied together at one end with clear tape, and b a similar device but with four silver
Ž .
Ž bead rings 0.8 cm diameter attached to four of the strands, two beads were attached to
the midpoints of two strands while the other two beads were attached at the bottoms of .
two different strands . Though the whole bead may have been too large for the chicks to grasp, they could still grip the 1.5-mm-wide ‘‘wall’’ surrounding the hollow 5 mm
centre in their beaks. Each device was suspended from the midpoints of each of the 36 cm walls. We recorded the chicks’ responses onto videotape using an overhead micro
camera during the 10 min observation period. This procedure was then repeated on each of 5 consecutive days and the position of each device was rotated daily. Upon reviewing
the videotapes we measured the latencies to peck, the numbers of pecks and pecking bouts directed at, and the accumulated times spent pecking each of the stimuli.
The chicks’ responses to the stimuli might be expected to change with repeated Ž
. exposure. Therefore, we calculated mean values for the full duration 5 days of the
experiment for each measure and then, because this was a two-sample case, we used the Ž
. Wilcoxon signed ranks test two-tailed to compare the pecking attention that each
Ž .
stimulus received. We also calculated the within-stimulus slopes patterns of response for each of the behavioural measures over the five days of exposure using the following
Ž .
Ž .
Ž .
Ž .
formula: Slope s y2 = D1 X y 1 = D2 X q 0 = D3 X q 1 = D4 X q 2 = Ž
. D5 X , where D s day, X s mean. We then compared the slopes for each stimulus
Ž .
using the Wilcoxon signed ranks test two-tailed in order to determine if any differ- ences were consistent over the 5 days. The Wilcoxon test was again used to compare D1
versus D5 values and thereby examine the development of responses to the stimuli. The latencies to peck at each of the two stimuli are clearly interdependent so these values
were pooled before the above test was carried out. On the other hand, there was plenty of time during each observation period when neither stimulus was being pecked, i.e.,
attention to one stimulus did not preclude pecking at the other. Therefore, the remaining measures were regarded as independent, thus allowing within-stimulus comparisons of
D1 versus D5 values.
7.2. Results and discussion The chicks pecked significantly sooner, directed more pecks and pecking bouts at,
Ž and spent more time pecking the non-beaded string rather than the beaded device Table
. 5 . There were no detectable differences between the slopes calculated for the non-beaded
Table 5 Meansstandard errors of the latencies to peck, the numbers of pecks and pecking bouts directed at, and the
Ž .
times spent pecking at each of the non-beaded and beaded string stimuli averaged over the five presentations and the results of Wilcoxon signed ranks tests of between-stimulus comparisons
Measure Stimulus
z P
Non-beaded Beaded
Ž . Lat.peck s
222.823.6 292.025.8
3.35 -
0.001 Ž
. Pecks no
17.92.8 9.31.8
3.84 -
0.0001 Ž
. Pecking bouts no
6.00.7 3.90.6
3.69 -
0.0001 Ž .
Time spent pecking s 48.07.8
22.74.7 3.85
- 0.0001
Ž . Ž
. Lat.s latency to; s sseconds; no s number; z sWilcoxon statistic
Ž Ž
. and beaded stimuli z s y1.68, 0.3, y1.26 and y1.91 for latencies y753, y960 ,
Ž .
Ž .
Ž .
pecks 45.3, 28.9 , bouts 16.9, 13.9 , and times 115.4, 61.6 , respectively, although the latter value approached significance at P s 0.056. In other words, despite the putative
Ž .
Ž attractive properties of spherical objects Dawkins, 1968 and shiny stimuli Rheingold
. and Hess, 1957 , the chicks’ interest in the string devices was actually reduced rather
than enhanced by the incorporation of silver bead rings in the present study. Thus, like those tested in Experiment 3, the present chicks preferred a simple stimulus to a more
complex one.
The patterns of the various responses with repeated exposure are shown in Fig. 4a,b,c and d. When the latencies to peck at either of the two devices were pooled, we found a
Ž significant decrease with repeated exposure, pooled means standard errors for days 1
. and 5 s 463.2 27.7 and 118.6 23.6, respectively, z s y5.88, P - 0.000 . Contin-
ued comparison of day 1 versus day 5 scores also revealed significant increases in the Ž
within-stimulus numbers of pecks z s y3.44 and y3.48 for non-beaded and beaded .
Ž devices, respectively, both P - 0.0001 , pecking bouts
z s y3.93 and y4.01, both
Ž . Ž .
Ž . Ž .
Fig. 4. a The latencies to peck at, b the numbers of pecks, c pecking bouts, and d times spent pecking at Ž
. Ž .
each of the non-beaded NB and beaded B devices when these were presented simultaneously for 10 min on each of 5 consecutive days in Experiment 5.
. Ž
. P - 0.000 and times spent pecking
z s y3.22, P - 0.002; z s y2.54, P - 0.02 . Thus, once again, the devices attracted more interest upon their repeated presentation.
8. General discussion
