Pecking preferences and pre-dispositions in domestic chicks: implications for the development of environmental enrichment devices

Transcription

1 . Applied Animal Behaviour Science Pecking preferences and pre-dispositions in domestic chicks: implications for the development of environmental enrichment devices R. Bryan Jones ), Nina L. Carmichael, Emma Rayner Roslin Institute Edinburgh, Welfare Biology Group, Roslin, Midlothian EH5 9PS, Scotland, UK Accepted 9 March 000 Abstract Environmental enrichment is thought likely to benefit chickens and farmers in many ways; these include reduced fearfulness and feather pecking and improved productivity. Enrichment devices would intuitively be more effective if they reliably attracted and sustained appreciable interest but many fail to do so. This may reflect the fact that the choice of stimuli often reflects availability and human preconceptions rather than a critical consideration of the birds preferences and pre-dispositions. We had previously identified string as a particularly attractive pecking stimulus for chicks and adult hens Gallus gallus domesticus. of a laying strain ISA Brown.. In the present study we found that chicks of another laying strain Lohmann Brown. also pecked sooner and more at a bunch of string than at chains or beads Experiment 1.. White or yellow strings were preferred to red, green or blue ones Experiment. and white string elicited more pecking than did combinations of white and yellow or of all five colours Experiment 3.. Varying the length and width of the bunches of string exerted no detectable effects on pecking Experiment 4. whereas incorporating small, shiny beads in the white string devices actually reduced pecking Experiment 5.. Virtually all the devices elicited progressively more interest with repeated presentation; this trend was particularly marked for white string. Collectively, the present findings demonstrate that young domestic chicks have clear and specific pecking preferences. Although the magnitude of response varied across experiments, white string consistently elicited the most interest. Our two main conclusions are:. i white or yellow strings were particularly attractive stimuli that drew increasing interest, at least in the short term, and ii. simple devices were ) Corresponding author. Tel.: q ; fax: q address: bryan.jones@bbsrc.ac.uk R.B. Jones r00r$ - see front matter q 000 Elsevier Science B.V. All rights reserved.. PII: S

2 9 R.B. Jones et al.rapplied Animal BehaÕiour Science preferred to more complex ones, or at least to those used here. q 000 Elsevier Science B.V. All rights reserved. Keywords: Chicken welfare; Environmental enrichment; Pecking devices; Preferences 1. Introduction Chickens will actively seek stimulation Mench, 1994; Jones, and the opportunity to engage in foraging and exploratory behaviours is considered particularly important to them Blokhuis, 1986; Appleby et al., 199; Rogers, 1995; Huber-Eicher and Wechsler, 1998; Newberry, For example, both chicks and adult hens readily investigated and manipulated non-food as well as food-related items Gvaryahu et al., 1994; Huber-Eicher and Wechsler, 1998; Jones and Carmichael, 1998, 1999a., broiler chickens readily moved from their home pens through a gate into a nearby area when this contained novel objects that were changed daily Newberry, 1999., and the introduction of conspicuous and manipulable objects into the previously least preferred halves of chicks home cages resulted in a numerical trend towards increased usage of those areas Jones and Carmichael, 1999b.. Despite this, intensively housed birds are often reared in barren, invariant environments that minimise the opportunities for exploration. Such environmental impoverishment can compromise the birds welfare by increasing fearfulness, depression, feather pecking and cognitive impairment as well as leading to reduced productivity Appleby et al., 199; Mench, 199; Jones, 1996, 1997; Wemesfelder and Birke, Encouragingly, environmental enrichment can reduce many of the harmful states identified above as well as increasing the chickens behavioural repertoire and improving their health and performance Jones, 198; Yasutomi and Adachi, 1987; Vestergaard et al., 1993; Braastad, 1990; Nicol, 199; Gvaryahu et al., 1994; Jones, Putative enrichment stimuli have included a wide variety of manipulable andror novel objects, foods, pictures or sounds, as well as intuitively desirable resources, such as nest boxes, perches, straw and pecking devices Jones, 1986; Braastad, 1990; Reed et al., 1993; Gao et al., 1994; Gvaryahu et al., 1994; Jones and Carmichael, 1999a; Jones and Rayner, Although most studies reported beneficial effects of enrichment, an occasional cautionary note has been sounded. For example, the provision of operant feeders, shoe laces, plastic rods and a commercially available enrichment item Agri-Toy. elicited alarm and actually increased social pecking in groups of floor-housed laying hens Lindberg and Nicol, Furthermore, some stimuli, e.g., baubles, motorised devices, Agri-toys, elicited much less interest than others and were ignored in time Braastad, 1990; Sherwin, 1993; Gao et al., 1994; Jones et al., 1996; Jones and Carmichael, 1999a.. Inconsistencies across studies may reflect the choice of enrichment stimuli according to their availability, cost and human preconceptions of what constitutes enrichment rather than a critical consideration of the chickens preferences and predispositions. Surprisingly, though pecking behaviour has received considerable attention; the available information on pecking preferences is limited, sometimes contradictory and, with a few exceptions see below., often of little strategic relevance. For example, it is accepted that young chicks have a strong propensity to peck at small, three-dimensional

3 R.B. Jones et al.rapplied Animal BehaÕiour Science objects Dawkins, 1968; Hogan, 1973; Rogers, However, the range of test stimuli has generally been small and a recent report Huber-Eicher and Wechsler, suggests that the above propensity might not always translate into a preference. Indeed, chicks showed more foraging behaviour when they had access to large polystyrene blocks or bundles of long-cut straw rather than to polystyrene beads or a layer of shredded straw, respectively Huber-Eicher and Wechsler, Similarly, although feathers are considered to be particularly attractive stimuli for pecking Appleby et al., 199., their attractiveness may depend on whether or not they are on the bird. Indeed, though gentle pecking at the feathers of other chicks appears as early as 3 days of age Blokhuis, personal communication., we found that young chicks pecked much more readily at string than at bunches of feathers collected from age-matched conspecifics Jones et al., Neither is there consensus concerning chicks preferences for pecking at certain colours even when the class of stimulus, e.g., food, is the same see Experiment.. In view of these apparent inconsistencies we attempted to establish the birds pecking preferences in a systematic manner by presenting pair-housed chicks with a choice of stimuli. Previous studies revealed that string was the most attractive of a number of stimuli presented to chicks of the ISA Brown laying strain Jones et al., 1997; Jones and Carmichael, 1999a.. We now asked if this preference would generalize to include chicks of another commercial laying strain and we assessed the effects of manipulating the component features of that type of stimulus eliciting the greatest interest in order to identify its most attractive form. Therefore, in Experiment 1 we measured the pecking preferences of pair-housed Lohmann Brown chicks for lengths of string, chains or beads when these were presented consecutively one stimulus per day. or simultaneously for 10 min on each of 3 consecutive days. Rationales for our choice of stimuli are given in the introductions to each experimental section. Preference was defined as the tendency for the chicks to peck sooner and more often at one stimulus than at the others. Having determined which stimulus elicited most interest we then varied its component features. Colour preferences were examined in Experiment ; here the chicks were simultaneously presented with five differently coloured white, yellow, blue, green or red. versions of the preferred stimulus. The effects of combining colours within a stimulus thus arguably increasing complexity. and of varying the size of the preferred device were studied in Experiments 3 and 4, respectively. Experiment 5 examined chicks responses to bunches of string that either incorporated small silver beads or not. We focused on only one sex in the present study because the duration persistence. of attention that chickens pay to specific stimuli is known to be sensitive to sex and to circulating levels of testosterone Andrew, We chose females for the present study because the number of laying hens kept in industry far exceeds that of cockerels.. General methods.1. Animals, housing and husbandry Five batches of female Lohmann Brown chicks were obtained from a commercial. supplier at 1 day of age one batch for each experiment. The numbers of chicks in each

4 94 R.B. Jones et al.rapplied Animal BehaÕiour Science batch varied according to experimental demands. Immediately upon receipt the chicks were allocated at random to pairs and then housed in wooden boxes measuring either 36=38=30 cm or 7=38=30 cm length=breadth=height.. The size of the boxes again reflected experimental demands. To obtain the smaller boxes we simply divided the larger ones into two halves with a wooden partition. One bird from each pair was always marked on the back of the head with indelible ink to facilitate later identification. Each box rested on 85-cm-high shelves and their wire-mesh floors 1-cm grid. were raised cm off the shelving in order to allow the passage of excreta. Wire-mesh lids prevented the chicks from escaping. Food layer starter mash. and water were provided ad libitum in white, semi-circular plastic hoppers suspended from the centre of one wall; this was the central partition in those boxes that had been divided into two compartments and one of the long walls in the non-partitioned ones. These hoppers could be removed and replaced remotely for maintenance purposes thus minimising visual contact with the attendant. They were replenished twice daily between 0900 to 0930 and 1630 to 1700 hours and they were always returned to the same location. The photoperiod ran from 0500 to 1900 hours and dull emitter heaters suspended above each box maintained an ambient temperature of approximately 68C. Supplementary warmth was provided by convector heaters if required. The birds then remained undisturbed, apart from maintenance, until a pre-test habituation procedure began at 4 days of age see below.. No chicks were sacrificed in this study; they were all returned to the Institute s rearing stock at the completion of each experiment... Test procedure and data collection In order to minimize the potential disturbance caused by observation at test, we exposed the birds to a sham test procedure when they were 4 days old. This involved removing the lid from each box, moving the overhead heater to one side, and suspending a micro camera see below. over the box for 10 min. Testing began at 0900 hours on the following day. The types of stimuli presented to the chicks and their positioning in the box varied according to the demands of each experiment. However, they were always suspended for 10 min at approximately equi-distant positions from the top of one or more of the cage walls so that the bottom of each stimulus was approximately cm off the floor. The devices were never suspended from the wall bearing the food and water hoppers. The chicks responses to these devices were then recorded on videotape during the 10 min observation period using a Panasonic Industrial Colour CCD micro camera WV-KS15 8 = cm, length = breadth. suspended from a gantry 50 cm above each box and connected to a video tape recorder. The camera was always moved into place before the stimuli were presented. This procedure was repeated on each of 3 Experiment 1. or 5 Experiments 5. consecutive days. Though the number of exposure days varied across experiments, test order was always randomized across boxes and across test days. When subsequently reviewing the videotapes we only recorded the behaviour of the marked chicks, i.e., one per box, because pair-housed chicks generally stay close together and often engage in the same activity. We measured the latencies from their introduction to the first peck at each of

5 R.B. Jones et al.rapplied Animal BehaÕiour Science the stimuli as well as the numbers of pecks and pecking bouts directed at each one. Bouts were recorded as discrete events if they were separated by a minimum of 5 s Jones and Carmichael, 1999a.. 3. Experiment 1: preferences for pecking at different types of stimuli presented consecutively or simultaneously In this experiment, the chicks were presented with three types of stimuli; these consisted of lengths of white string, white wooden beads strung together or chrome chain. Apart from its practicability, we chose string for two other reasons. Firstly, at least one turkey farmer routinely provides baler twine as pecking material for his birds and reports substantial interest Parker, Secondly, string was pecked much more often than feathers, beads or baubles Jones et al., 1997; Jones and Carmichael, 1999a. by ISA Brown chicks. White or yellow string also elicited considerable interest in individually caged adult hens of the same strain Jones and Carmichael, By using Lohmann Brown chicks in the present experiment we were able to determine if this preference for string generalized to include another strain of laying chickens. Lengths of beads were selected as another stimulus because chicks peck readily at small spherical objects, including beads Dawkins, 1968; Rogers, Although the beads used here were 0.8 cm in diameter and thereby difficult for the chicks to grip in their beaks, it was thought that they might have borne some super-stimulus resemblance to grain or other seeds. Finally, chains were included because of anecdotal reports from farmers that they are readily pecked by birds kept on the floor in industry. It was conceivable that the chicks preferences might be more or less marked if they received a choice of stimuli to peck at rather than just one. Therefore, the stimuli were presented singly on consecutive days to the chicks in half of the boxes whereas the other chicks received simultaneous exposure to all three devices Methods Seventy-two chicks were randomly allocated to 36 pairs and each pair was housed in one half 38=36=30 cm. of each of 18 wooden boxes see above.. Three pecking stimuli string, beads, chain. were used. First, the string device consisted of three strands of white polypropylene twine, each was 8 cm long and approximately 0.3 cm wide. The strands were held firmly together at one end with a 0.5-cm-wide strip of white plastic tape. Second, 10 matte white wooden beads each measuring 1=0.8 cm, width=depth. were strung together with clear nylon line to form a device that was 8 cm long. The third stimulus consisted of a single 8 cm length of chrome plated chain with 1-cm links; the chicks could easily grip the solid parts in their beaks because they were just 1 mm thick. Thus, the lengths 8 cm. and widths approximately 1 cm. of each device were similar. Each stimulus was suspended from the top of a cage wall in a central position with a length of clear nylon monofilament fishing line. Each of these devices moved freely if pecked, pushed or pulled, but because

6 96 R.B. Jones et al.rapplied Animal BehaÕiour Science of their rigidity, the beads and chain moved further and quicker when pecked than did the string. Each pair of chicks was randomly assigned to one of two treatment groups. Thus, 18 pairs received simultaneous exposure to each of the three stimuli string, beads, chain. for 10 min on each of 3 consecutive days. The positions of the stimuli were randomised across the 18 compartments and across exposures with the proviso that none was ever presented on the same wall as the food and water hoppers. In the consecutive exposure treatment the stimuli were presented singly for similar periods on each of the 3 days to the remaining 18 pairs. Here, the order of presentation was randomised within a balanced design, e.g., six pairs received string, beads and chain on days 1, and 3, respectively, while six received chain, beads and string on the corresponding days, etc. The wall from which the single stimulus was suspended was also determined at random each day. The chicks responses were recorded on videotape for later analysis of the behaviour patterns described above. The scores recorded for each bird across all 3 days were summed and then averaged to give a single value for each behaviour pattern for each chick. The data sets were non-normally distributed and were therefore transformed to square roots. The main effects of treatment stimulus and method of presentation. were examined using analysis of deviance Genstat 5.3 Committee, Results and discussion The Lohmann Brown chicks used in the present experiment pecked significantly sooner and more often at the bunch of string than at either beads or chains regardless of whether these stimuli were presented singly or simultaneously on three consecutive days Table 1.. These findings are consistent with previous reports that string elicited more interest from ISA Brown chicks than other stimuli that we had thought likely to be attractive, e.g., baubles, beads and feathers Jones et al., 1997; Jones and Carmichael, 1999a.. Thus, the strong attraction towards string is common to chicks of two different laying strains. It is not considered likely to reflect differences in the chicks ability to manipulate the stimuli because they could grip both chain 1 mm. and string 3 mm. in their beaks. The method of presentation was also influential in that the stimuli were pecked significantly more when they were presented simultaneously rather than singly and this was particularly true for string. These observations may have important practical implications. Firstly, they suggest that the presentation of multiple rather than single enrichment stimuli may be more effective in eliciting interest. Secondly, simultaneous screening of selected pecking stimuli would greatly accelerate the identification of particularly attractive ones. Thirdly, simultaneous presentation of multiple devices allows assessment of potential conservatism in stimulus choice see below.. The significant interactions found between the effects of stimulus type and the method of presentation probably reflect the fact that some chicks switched preferences from chain to beads and vice versa across days. Interestingly, none switched their preference from string. The fact that there was only one value per day for each measure precluded meaningful statistical analysis of the evolution of pecking upon repeated presentation of

7 R.B. Jones et al.rapplied Animal BehaÕiour Science Table 1 Responses means"standard errors. of pair-housed chicks to string, beads and chain devices when these were presented singly or simultaneously for 10 min on 3 consecutive days and the results and probability values of an analysis of deviance of the effects of stimulus, method of presentation and their interaction Method of Measure Stimulus presentation String Beads Chain Single Lat. peck. s 437.4" " "15.1 Pecks no. 1.78" " "0.06 Pecking bouts no. 1." " "0.06 Simultaneous Lat. peck. s 6." " ".0 Pecks no. 8.83" " "0.07 Pecking bouts no. 5.11" " "0.07 Measure Effects of Stimulus S. df s. Method M. df s1. S=M df s. Lat. peck x s1.08 x s0.10 x s0.30 P N.S. N.S. Pecks x s61.07 x s4.61 x s14.14 P P P Pecking bouts x s44.55 x s10.40 x s1.08 P P P Lat.slatency to; s sseconds, no snumber; df sdegrees of freedom; N.S.snot significant. the stimuli. However, descriptive graphs Fig. 1a and b reveal that the latency to peck at string decreased sharply and the number of pecks increased progressively over the three presentations. The practical implications of such apparent sensitization of response, rather than habituation, are covered in the General Discussion... Fig. 1. a The latencies to peck at and b the numbers of pecks delivered at each of the string, bead and chain devices when these were presented simultaneously for 10 min on each of the test days in Experiment 1.

8 98 R.B. Jones et al.rapplied Animal BehaÕiour Science Experiment : preferences for different colours of string 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 objects are particularly attractive reviewed by Rogers, 1995; Roper and Marples, conflict with reports that chicks avoid blue beads Andrew et al., and blue food Taylor et al., 1969; Jones, 1986., that adult hens are reluctant to peck at blue objects Wood-Gush, 1971., and that red may be a warning colouration that elicits avoidance Roper, 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 reported as yellow, brown, red, white or blue Bessei and Bruckman, 1977; Hurnik et al., 1977; Roper, 1990; Roper and Marples, 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 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. 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

9 R.B. Jones et al.rapplied Animal BehaÕiour Science 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. 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 then examined using two-way analysis of deviance McCullagh and Nelder, 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.. Results and discussion Upon pooling the results from all 5 test days, we found significant differences in the chicks responses to the different devices Table.. They pecked sooner and directed more pecks and bouts of pecking at white or yellow string than at any of the other three colours, though white seemed marginally more attractive than yellow Table 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 blue or orange bunches Jones and Carmichael, The chicks were also consistent here in the order in which they pecked the different stimuli across the 5 days x s4.6, dfs144, P-0.05., i.e., there was significant concordance within boxes in the choice of colours. Similarly, there was significant agreement df s 4, P across the 36 chicks in the order of colours pecked within each test day x s4.48, 0.16, 41.76, and 5.9 for days 1,, 3, 4 and 5, respectively.. The accumulated numbers of times that each colour was the first to be pecked also differed significantly x s49.7, dfs4, P and followed the order of white 56., yellow 45., red 3., green 15. and blue 9.. The latencies to the first peck at any of the stimuli, regardless of colour, fell significantly H s 88.08, df s 4, P with repeated exposure. The cumulative Table The latencies to peck and the numbers of pecks and pecking bouts directed at each of the differently coloured strings averaged across all 5 test days means"standard errors. and the results of Friedman two-way analyses of variance df s4. Measure Colour S P White Yellow Red Green Blue Lat. Peck. s 35.0" " " " " Pecks no. 7.51" "0.81.4" " " Pecking bouts no. 4.9" " " " " df sdegrees of freedom; Lat. peckslatency to peck; s sseconds; no snumber

10 300 R.B. Jones et al.rapplied Animal BehaÕiour Science Fig.. 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. means, with their standard errors, were 367.0"43.0, 05.1"35.4, 83."1.0, 35.0" 16.0 and 3.1" 15.4 for days 1 through 5, respectively. Analysis of deviance revealed that the numbers of pecks at the stimuli x s78.74, dfs4, P and of pecking bouts x s 63.57, df s 4, P increased markedly with repeated exposure and that the white and yellow strings consistently attracted more pecking than the red, blue or green bunches x s46.64, dfs4, P and x s5.79, dfs4, P for pecks and bouts, respectively.. There were no significant interactions between colour and repeated presentation for the numbers of pecks x s 1., df s 4, P) or pecking bouts x s0.95, dfs4, P) 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. a and b, respectively. The present findings clearly demonstrate that white or yellow string elicited substantially more pecking than did the other devices. Indeed, the chicks showed comparatively 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 exposed is healthier Fox, 1986; Renner and Rosenzweig, and less boring Wemelsfelder, 1985., that structural, visual and textural complexity encourages interaction between the animal and its environment Dember et al., 1957; McGrew et al., 1986;

11 R.B. Jones et al.rapplied Animal BehaÕiour Science Chamove, 1989., and that environmental complexity reduces distress in captive animals Snyder, White and yellow were identified as the most attractive colours in Experiment. A combination of white, yellow and green string also readily attracted pecking by ISA 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 experiment, 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 colours tested above white, yellow, green, red, blue Methods The partitions were removed from the wooden boxes described above so that each one provided an area measuring 7 = 38 = 30 cm length = breadth= height.. Thirty-six 1-day-old females were housed in pairs in 18 of these boxes. Husbandry and maintenance procedures were similar to those described previously and the birds remained undisturbed until testing began at 5 days of age. Four test stimuli were used here. These were either:. a five strands of white W. polypropylene twine,. b five yellow Y. strands,. c three white and two yellow W q Y. or two white and three yellow strands the two combinations were equally represented., and d. one strand each of white, yellow, green, red and blue twine 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 7-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. 5.. Results and discussion The chicks pecked sooner at the white string than at any of the other devices; this stimulus also elicited more pecks and pecking bouts Table 3, and below.. The chicks preferences were almost invariably W)Y)WqY)M-C. Unlike the conservatism shown by chicks in the previous experiment, those tested here did not show consistency in the order in which they pecked the stimuli across test days x s5.71, dfs54, P) Similarly, significant agreement across chicks and within days in the order of pecking at each stimulus was only achieved on days 1 x s14.04, dfs3, P and 3 x s9.18, dfs3, P 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

12 30 R.B. Jones et al.rapplied Animal BehaÕiour Science Table 3 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 two-way analyses of variance df s3. Measure String stimuli S P White Yellow WhiteqYellow Multi-coloured Lat. peck. s 445.3" " " " Pecks no. 1.96" " " " Pecking bouts no. 1.17" " " " df sdegrees of freedom; Lat. peckslatency to peck; s sseconds; no snumber significant difference between the numbers of times each stimulus was the first to be pecked x s14.47, dfs3, P ; this followed the pattern of W 0., Y 11., WqY 1. and M-C.. Collectively, the latencies to peck at any of the stimuli, regardless of their nature, fell significantly H s 1.30, df s 4, P with repeated exposure; the cumulative means all stimuli pooled. and their SEMs were 495.8"47.4, 437.7"53.3, 355.7" 6.5, 63.3"60.1 and 54.4"66.7 for days 1 through 5, respectively. Analysis of deviance also revealed that the stimuli attracted progressively more pecks Fig. 3b;. x s39.43, dfs43, P and pecking bouts x s19.78, dfs4, P upon repeated presentation and that W or Y strings were generally more attractive than the WqY 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 exposure Experiment, Jones and Carmichael, 1998; 1999a.. Furthermore, the differ- Fig. 3.. a The latencies to peck at and. b the numbers of pecks delivered at each of the white W., yellow Y., white plus yellow WqY. or multi-coloured M-C. string devices when these were presented simultaneously for 10 min on each of the test days in Experiment 3.

13 R.B. Jones et al.rapplied Animal BehaÕiour Science 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 responses of young chicks Rogers, 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 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 into the home cage when the chicks were 5 days old. The devices consisted of:. a four strands each measuring 4 cm in length,. b four strands of 8-cm length,. c eight strands of 4 cm length and,. d eight strands of 8 cm length. The first two devices were approximately 1. cm wide whereas the other two were.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. 6.. Results and discussion Using pooled results from all 4 test days. we found no significant differences in the latencies to peck Ss1.6, dfs3, Ps or in the numbers of pecks Ss0.18, dfs3, Ps or pecking bouts Ss1.97, dfs3, Ps directed at any of the 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.

14 304 R.B. Jones et al.rapplied Animal BehaÕiour Science Table 4 Means"standard 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 Measure Number and length cm. of strings 4=4 4=8 8=4 8=8 Lat. peck. s 374.4" " " "7. Pecks no..03" " " "0.98 Pecking bouts no. 1.3" " " " cm scentimetres; Lat. peckslatency to peck; s sseconds; no snumber Although the latency to the first peck, regardless of stimulus, fell from 150.8" 41.4 on day 1 to 131.3"5.9 s on day 4, this trend was not significant Hs5.87, dfs3, Ps0.1.. Analysis of deviance also revealed that there were no effects of stimulus type or repeated exposure on the numbers of pecks x s1.47, dfs3, P)0.80; x s3.99,. dfs3, P)0.30 or pecking bouts x s0.10, dfs3, P)0.99; x s.80 dfs3,. P)0.30, neither were there any significant interactions x s4.5, dfs9, P)0.80; x s3.0, dfs9, P) 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 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 propensity to peck at small spherical objects Dawkins, 1968; Rogers, Furthermore, shiny stimuli are thought to be not only attractive but perhaps even supernormal Rheingold and Hess, Therefore, in the present experiment we examined the effects of incorporating small shiny bead rings in the white string devices 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 old. The stimuli consisted of:. a eight strands of 8-cm long, white polypropylene twine tied together at one end with clear tape, and. b a similar device but with four silver bead rings 0.8 cm diameter. attached to four of the strands, two beads were attached to

15 R.B. Jones et al.rapplied Animal BehaÕiour Science 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 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 Wilcoxon signed ranks test two-tailed. to compare the pecking attention that each 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 formula: Slope sy = D1 X. y 1 = D X. q 0 = D3 X. q 1 = D4 X. q = D5X., where Dsday, Xsmean. We then compared the slopes for each stimulus using the Wilcoxon signed ranks test two-tailed. in order to determine if any differences 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.. Results and discussion The chicks pecked significantly sooner, directed more pecks and pecking bouts at, 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 Means"standard errors of the latencies to peck, the numbers of pecks and pecking bouts directed at, and the 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 Lat.peck. s.8" " Pecks no. 17.9".8 9.3" Pecking bouts no. 6.0" " Time spent pecking. s 48.0"7.8.7" Lat.slatency to; s sseconds; no snumber; zswilcoxon statistic

16 306 R.B. Jones et al.rapplied Animal BehaÕiour Science and beaded stimuli z sy1.68, 0.3, y1.6 and y1.91 for latencies y753, y960., pecks 45.3, 8.9., bouts 16.9, 13.9., and times 115.4, 61.6., respectively, although the latter value approached significance at P s In other words, despite the putative attractive properties of spherical objects Dawkins, 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 significant decrease with repeated exposure, pooled means" standard errors for days 1 and 5s463."7.7 and 118.6"3.6, respectively, zsy5.88, P Continued comparison of day 1 versus day 5 scores also revealed significant increases in the within-stimulus numbers of pecks z sy3.44 and y3.48 for non-beaded and beaded devices, respectively, both P , pecking bouts z sy3.93 and y4.01, both Fig. 4.. a The latencies to peck at,. b the numbers of pecks,. c pecking bouts, and. d times spent pecking at 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.

17 R.B. Jones et al.rapplied Animal BehaÕiour Science P and times spent pecking zsy3., P-0.00; zsy.54, P-0.0. Thus, once again, the devices attracted more interest upon their repeated presentation. 8. General discussion Mench concluded that a trial-and-error approach to the design of environmental enrichment devices could be avoided by presenting animals with objects that vary systematically and then allowing them to choose which they prefer. She also concluded that this approach is used too infrequently in enrichment research Mench, In similar vein, Newberry and Jones identified the need for more critical thought regarding the design of enrichment objects intended to achieve specific goals. Therefore, the present findings are particularly pertinent because not only did we assess the preferences of domestic chicks for pecking at one of three types of stimuli but we then systematically varied the appearance of the most attractive one. Our findings provide valuable insights into the pecking preferences of female domestic chicks that are of strategic as well as fundamental interest. They clearly demonstrate the importance of some of the component features colour, simplicity. as well as the type of pecking stimuli presented. They also indicate the likely existence of predispositions for pecking at certain stimuli because none of our chicks had previously encountered any of the devices used. Had we designed our pecking devices purely on the basis of previous reports that chicks show a strong propensity to peck at small, three-dimensional objects Dawkins, 1968; Hogan, 1973; Rogers, and that red and blue see Rogers, 1995; Roper and Marples, or shiny Rheingold and Hess, stimuli were particularly attractive, it is highly unlikely that we would have chosen the stimulus string. that proved to be most attractive here and in each of our other studies Jones and Carmichael, 1998; 1999a.. String elicited more pecking by young chicks than a bunch of feathers, a length of coloured leg bands, or baubles Jones et al., 1997; Jones and Carmichael, 1999a.. The present results showed that this stimulus was also more attractive than a length of chain or a string of beads. They also demonstrated that such attraction to string is common to chicks of two laying strains ISA Brown, Lohmann Brown.. Furthermore, although the magnitude of the chicks responses varied across experiments, probably reflecting batch effects, white string was consistently the most attractive stimulus. Because much pecking activity is directed at the ground Broom, beads might have been more attractive had they been presented singly and loose on the floor of the cage rather than strung together and suspended from the top of the wall. However, strategic considerations demanded vertical presentation. For example, the provision of small, non-edible particles on the floors of cages or pens in industry is likely to have limited practical value because they could be lost in the litter, ingested which could lead to intestinal complications., or contaminated with faeces. Indeed, as well as hygiene considerations, pigs rapidly lost interest in enrichment objects when they became soiled with excreta Grandin, A report that weaned pigs play more with fixed toys rather than free ones Blackshaw et al., also supports our use of fixed devices here.

18 308 R.B. Jones et al.rapplied Animal BehaÕiour Science Why should string be more attractive than the other stimuli? Bead and chain devices moved more rapidly when pecked and it could be argued that the chicks found this property slightly aversive, or at least not as attractive as the slower movement of the string. It could also be suggested that the attraction to string reflected its resemblance to stimuli that might be inherently supernormal, such as grass, straw, twigs or worms. Alternatively, although the chicks could grasp the solid 1 mm wide links of the chain Experiment 1. or the 1.5 mm surround of the silver bead Experiment 5. in their beaks, we gained a strong subjective impression that they manipulated the devices in different ways. As well as pecking and pulling at the string they often closed their mandibles around it, drew it through their beaks, and sometimes teased the strands apart. Though we do not suggest that the chicks were actually preening the string, some of these actions resembled preening behaviour Wood-Gush and Rowland, Therefore, a more realistic interpretation of the highly attractive properties of string might be that its manipulation provided more positive feedback than did that of more solid stimuli like beads, rings, chains, baubles, leg bands or rubber tubing. The chicks showed distinct colour preferences; when presented simultaneously with five bunches of differently coloured string they pecked sooner and more often at white or yellow than at green, blue or red. Similarly, adult hens showed much greater interest in white or yellow than in orange or blue strings Jones and Carmichael, It is unlikely that these preferences reflected greater brightness and increased visibility of white and yellow for a number of reasons. Firstly, the chicks home cages were well lit and visual sensitivity remains high in chickens even in near darkness Charles, Secondly, chickens can distinguish between coloured stimuli regardless of their relative brightness Lashley, Thirdly, if the chicks had found the red, green and blue strings difficult to see, we would not have expected the observed increase in pecking at these stimuli upon repeated presentation. Sherwin reported that caged laying hens pecked more at simple green objects than at red, orange, yellow, blue or white ones and he attributed this to a presumed adaptive value of selecting green food. Conversely, green string was pecked much less than white or yellow ones in the present study. Our findings also contrast with previous reports that red and blue objects elicited most pecking by chicks Davis and Fischer, 1978; Clifton and Andrew, Feathers dyed red or blue were also pecked by laying hens during two exposures of 15 min Cloutier et al., 000. but since these were the only colours used inferences concerning wider preferences could not be made. However, our results are consistent with suggestions that blue food and objects were aversive to chicks and adult hens Taylor et al., 1969; Wood-Gush, 1971; Andrew et al., 1981; Jones, and that red might act as a warning signal and thereby elicit avoidance Roper, A similar unlearned aversion to red was also reported in northern Bobwhite quail when they were presented with coloured pinheads Mastrota and Mench, The literature concerning colour preferences in chickens is littered with inconsistencies but this may reflect differences across studies in the stimuli used, the contexts in which they were presented, the background genome, previous experience and perhaps the age of the birds at test. Our findings may reflect an inherent attraction to white and yellow stimuli but it might also be argued that attractiveness was simply associated with familiarity. In other