Experiment 2: preferences for different colours of string

4. Experiment 2: preferences for different colours of string

Ž . Because chickens have good colour vision Rogers, 1995 , colour is considered likely to be an important attribute of any enrichment device. However, there is little consensus of opinion concerning colour preferences. For example, suggestions that red and blue Ž . objects are particularly attractive reviewed by Rogers, 1995; Roper and Marples, 1997 Ž . conflict with reports that chicks avoid blue beads Andrew et al., 1981 and blue food Ž . Taylor et al., 1969; Jones, 1986 , that adult hens are reluctant to peck at blue objects Ž . Wood-Gush, 1971 , and that red may be a warning colouration that elicits avoidance Ž . Roper, 1990 . Agreement has not even been reached regarding the favoured colours of the same type of stimulus. Thus, chicks’ preferred colour of food has been variously Ž reported as yellow, brown, red, white or blue Bessei and Bruckman, 1977; Hurnik . et al., 1977; Roper, 1990; Roper and Marples, 1997 . In the present experiment we asked if chicks preferred to peck at string of a particular colour by presenting them simultaneously and repeatedly with five bunches of string, each of a different colour. These were red, blue, green, yellow or white. 4.1. Methods Seventy-two female chicks were obtained at 1 day of age, immediately allocated into pairs and then housed under the conditions described above. They remained undisturbed until the pre-test acclimatisation procedure was carried out 3 days later and testing began when they were 5 days old. Ž The stimuli comprised five differently coloured bunches of string blue, green, . yellow, white or red . Each device consisted of three 8-cm-long strands of the same colour of polypropylene twine tied together at one end with clear tape. These were suspended from the tops of the cage walls at equidistant intervals; thus two hung from each of the 36 cm long walls and one from the wall facing the food and water hoppers. The daily position of each bunch was determined using a quasi-random design such that each colour was presented in each of the five positions across the five test days. An overhead camera recorded the chicks’ behaviour onto videotape. The stimuli were removed immediately after each 10-min observation period and introduced into the next in a randomly determined order of cages. All testing was completed between 0900 to 1700 hours. This procedure was repeated on each of 5 consecutive days. Upon reviewing the videotapes we recorded the latencies to peck as well as the numbers of pecks and pecking bouts directed at each stimulus. We also recorded which bunch of strings was pecked first by each bird on each of the 5 days. The latency data were not independent and they were therefore converted to ranks. Because the effects of treatment and of repeated exposure could not be examined simultaneously, a number of independent analyses were carried out. First, the latencies to peck each of the coloured strings on each of the 5 test days were summed and then averaged to give a single value for each chick; these were then subjected to a Friedman two-way analysis of variance. Second, the consistency of the order in which the strings were pecked on each of the 5 days was assessed using the Kendall coefficient of concordance. Third, the effects of repeated exposure on the latencies to the first peck at any string, regardless of colour, were examined using the Kruskal–Wallis one-way analysis of variance. The inter-dependency of data precluded analysis of time trends within colours. Ž Colour preference effects on the numbers of pecks and pecking bouts averaged . across all 5 test days were examined initially using the Friedman two-way analysis of variance. Because the data sets for both the numbers of pecks and of pecking bouts approximated over-dispersed Poisson distributions, they were also analysed using a logarithmic link and the effects of colour, repeated exposure and their interaction were Ž . then examined using two-way analysis of deviance McCullagh and Nelder, 1989 . The numbers of times that each coloured bunch of string was the first to be pecked on each of the 5 days were summed to give one value for each colour. These values were then compared using a one-way chi-squared test. It was not possible to compare totals across days or colours independently because the counts fell below 5 in too many cells. 4.2. Results and discussion Upon pooling the results from all 5 test days, we found significant differences in the Ž . chicks’ responses to the different devices Table 2 . They pecked sooner and directed more pecks and bouts of pecking at white or yellow string than at any of the other three Ž colours, though white seemed marginally more attractive than yellow Table 2 and see . below . These preferences are similar to those shown by adult ISA Brown hens that also pecked considerably sooner and more often at white and yellow string than they did at Ž . blue or orange bunches Jones and Carmichael, 1998 . The chicks were also consistent here in the order in which they pecked the different stimuli across the 5 days Ž 2 . x s 224.26, df s 144, P - 0.05 , i.e., there was significant concordance within boxes Ž . in the choice of colours. Similarly, there was significant agreement df s 4, P - 0.001 Ž 2 across the 36 chicks in the order of colours pecked within each test day x s 24.48, . 20.16, 41.76, 31.68 and 25.92 for days 1, 2, 3, 4 and 5, respectively . The accumulated numbers of times that each colour was the first to be pecked also differed significantly Ž 2 . Ž . Ž . x s 49.72, df s 4, P - 0.001 and followed the order of white 56 , yellow 45 , red Ž . Ž . Ž . 32 , green 15 and blue 9 . The latencies to the first peck at any of the stimuli, regardless of colour, fell Ž . significantly H s 88.08, df s 4, P - 0.001 with repeated exposure. The cumulative Table 2 The latencies to peck and the numbers of pecks and pecking bouts directed at each of the differently coloured Ž . strings averaged across all 5 test days meansstandard errors and the results of Friedman two-way analyses Ž . of variance df s 4 Measure Colour S P White Yellow Red Green Blue Ž . Lat. Peck s 235.020.8 259.619.2 357.122.5 391.820.7 453.018.6 82.03 - 0.001 Ž . Pecks no 7.510.65 7.000.81 2.420.50 2.700.44 1.130.26 100.79 - 0.001 Ž . Pecking bouts no 4.290.35 3.980.36 1.730.27 0.920.18 1.800.22 92.87 - 0.001 Ž . Ž . df sdegrees of freedom; Lat. peck s latency to peck; s sseconds; no s number 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