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Exploratory behaviour of young domestic fowl
Applied Animal Behaviour Science 63 Ž1999. 311–321
Exploratory behaviour of young domestic fowl Ruth C. Newberry
a,b,)
a
Center for the Study of Animal Well-being, Department of Animal Sciences, Washington State UniÕersity, Pullman, WA 99164-6520, USA b Department of Veterinary and ComparatiÕe Anatomy, Pharmacology and Physiology, Washington State UniÕersity, Pullman, WA 99164-6520, USA Accepted 3 February 1999
Abstract Under the hypothesis that young domestic fowl, Gallus gallus, are motivated to seek opportunities to explore novel stimuli, it was predicted that broiler chickens would show greater motivation to enter peripheral space if it contained Ža. novel objects Žchanged daily. than if it was Žb. empty or contained Žc. essential resources Žfood, water, heat. or Žd. supplementary resources Žpeat moss, straw bale, elevated platform.. Sixteen pens, each containing 100 chickens, were set up with a home area containing essential resources and an adjacent peripheral area of the same size to which the chickens were allowed access for 3 h daily by opening a gate. There were four replicate pens on each of four treatments varying in the resources Ža–d. provided in the peripheral area. During week 6, continuous video recordings showed that more chickens on the novel objects treatment ran into the peripheral area during the first 5 min after the gates were opened than did chickens on the other three treatments Ž P - 0.001.. From weeks 2 to 6, scan samples at hourly intervals while the gates were open indicated that, on average, the number of chickens in the peripheral area was significantly higher on the essential resources treatment, and significantly lower on the empty treatment, than on the novel objects and supplementary resources treatments. Chicken survival, body weight and feed efficiency did not differ between treatments Ž P ) 0.05.. The results support the hypothesis that the chickens were motivated to seek opportunities to explore novel stimuli. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Broiler chicken; Exploration; Boredom; Environmental enrichment; Use of space; Animal welfare
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Tel.: q1-509-335-2957; fax: q1-509-335-4650; e-mail: [email protected]
0168-1591r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 1 5 9 1 Ž 9 9 . 0 0 0 1 6 - 7
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1. Introduction Young domestic fowl, Gallus gallus domesticus, being intensively reared for meat are typically kept indoors in flocks of several thousand chickens on a litter-covered floor. Sources of food, water and supplementary heat are distributed abundantly and predictably throughout the available space so that travel time, search time and competition for resources are minimised. In countries with cold winters, chicken houses are usually windowless and provided with low intensity lighting. The ambient temperature is lowered gradually as the chickens grow and temperature fluctuations are controlled within narrow limits. Most broiler chickens are uniformly white-feathered, and kept in flocks of the same age and genetic background. These conditions differ sharply from the conditions experienced by chickens during their evolutionary history. It is only within the last 50 years that chickens have been confined indoors for intensive production. Prior to this time, they were exposed to a variety of vegetation, predators, prey, weather conditions and seasonal changes ŽCollias and Collias, 1967; McBride et al., 1969.. Under these conditions, learning has survival value ŽAmbrose, 1972; Stamps, 1995.. During their evolutionary history, domestic fowl have had life history characteristics associated with the evolution of intellect, including life in stable social groups with overlapping generations ŽHumphrey, 1976., central place foraging and exploitation of a wide variety of prey ŽMather, 1995; Mench, 1998.. There is ample evidence of brain plasticity associated with learning in the domestic fowl ŽKolb and Whitshaw, 1998.. Exploratory behaviour involves information gathering through active interaction with novel stimuli in the environment ŽBerlyne, 1960.. Boredom results from a chronic lack of opportunities for active interaction with the environment ŽWemelsfelder and Birke, 1997.. The housing of broiler chickens in a relatively constant environment throughout their lifetime raises the question of whether the chickens’ well-being is compromised by boredom. After an initial period of exploration, chickens will habituate to stimuli in their housing environment that have no perceived positive or detrimental effects. In the absence of new sources of novelty, the environment becomes highly predictable and the chickens may no longer be stimulated to perform exploratory behaviour. If so, the lack of novelty may be associated with impaired brain development ŽRenner and Rosenzweig, 1987. and boredom. Although chickens exhibit fear-related behaviour when novelty is encountered in open field tests ŽMurphy and Wood-Gush, 1978., these tests involve placing animals in a novel environment, usually alone, and without refuges or escape routes ŽWelker, 1957.. When chickens are able to control their exposure to novelty through voluntary approach and retreat, a higher level of exploratory investigation is predicted. The present experiment examined whether broiler chickens would voluntarily enter areas that provided opportunities for interaction with stimuli not found in a typical broiler chicken house. Such behaviour could point out inadequacies in the typical housing environment that may impact upon the well-being of broiler chickens. Chickens were given voluntary access to areas containing either Ža. no resources, Žb. essential resources that were also present in the home environment, Žc. novel objects, or Žd. supplementary resources considered to have biological value to the chickens and not
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available in the home environment. It was hypothesised that broiler chickens are motivated to seek opportunities to explore novel stimuli. According to this hypothesis, it was predicted that the chickens would be more motivated to enter a peripheral area if it contained novel objects than if the area contained no resources, essential resources or supplementary resources.
2. Methods 2.1. Animals and husbandry Sixteen floor pens were set up in a light-tight, insulated chicken house. The fences between each pen were covered with a black plastic visual barrier. A 4.3-m long transparent wire mesh partition divided each pen into two halves, each measuring 4.3 m = 5.0 m. The partition contained a 1.5-m long wire mesh gate at one end. One half of the pen was designated as the home area, and the other half as the peripheral area. All home areas were furnished identically with a gas brooder Ž1.2 m diameter. in the centre of the area, a water trough Ž234 cm long. on either side of the brooder and a tube feeder Žpan diameter 35.6 cm, 1–19 days; 41.9 cm, 20–42 days. in each corner. A 5-cm deep layer of fresh softwood shavings was spread over both halves of each pen. A total of 1600 male Peterson= Arbor Acre chicks, vaccinated against Marek’s disease, were obtained from a commercial hatchery. One hundred randomly selected chicks were placed in each of the 16 home areas. The chicks were kept in a corral under the brooder until day 7, when the corrals were removed. From 8 to 41 days, with the exception of day 21, the gates were opened to give all chickens access to the other half of their pen Žperipheral area. from 0945 to 1245 h daily. All chickens were fed a 23% protein starter diet from 0 to 21 days and a 20% protein grower diet from 21 to 42 days. Food and water were provided ad libitum. Light intensity was 20 lx, 0–6 days and 5 lx, 7–42 days, as measured 23 cm above the litter, directly beneath the two 100 W–130 V frosted incandescent light bulbs per pen. An increasing photoperiod lighting program Ž23L:1D, 0–3 days; 6L:18D, 4–14 days; 10L:14D, 15–21 days; 14L:10D, 22–28 days; 18L:6D, 29–35 days, 23L:1D, 36–42 days. was used to minimise mortality and leg disorders ŽClassen et al., 1991; Blair et al., 1993.. The photoperiod started at 0730 h daily. Temperature under the brooders was reduced by 28C weekly, from 318C at 1 day to 218C at 35 days. 2.2. Experiment treatments The peripheral area of each pen was assigned to one of four treatments. Each treatment was replicated in four pens in a randomised block design. The stimuli provided in each treatment were in place from 1 to 41 days. Chickens, thus, had the opportunity to become familiar with the view of the peripheral area before the gates were opened for the first time at 8 days.
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In the ‘empty’ treatment, the peripheral area was an empty space with no furnishings or resources apart from wood shavings on the floor Žalso present in all other peripheral and home areas.. In the ‘essential resources’ treatment, the peripheral area contained four feeders, two water troughs and a gas brooder in the same layout, and operated in the same manner, as in the home area. In the ‘supplementary resources’ treatment, the peripheral area was equipped with Ža. a bale of wheat straw Žbaler twine removed., Žb. a wooden platform Ž1 m L = 1 m W = 30 cm H, with wire mesh to prevent chickens from going underneath. with a wooden ramp Ž1 m L = 10 cm W = 2 cm D . attached to the centre of one side, and Žc. a wooden platform without wire mesh, turned upside down Žwalls 10 cm high. and kept filled with peat moss. These items were not available in the home area and were expected to have biological relevance to the chickens ŽNewberry, 1995. by stimulating foraging behaviour Žpecking, scratching, manipulating., locomotory behaviour Žclimbing, jumping, flying., and dust bathing, respectively. The straw bale, wooden platform and peat moss box were arranged approximately 2 m apart in a triangle, in the centre of the peripheral area, with the point of the triangle towards the central partition between the home and peripheral areas. In the ‘novel objects’ treatment, three novel objects were placed in the peripheral area on day 1 in the same triangular layout as in the supplementary resources treatment. From 2 to 41 days, the novel objects were replaced daily between 0800 h and 0900 h. Each set of three objects was used only once in each pen. The objects Ž n s 123. were non-nutritive and non-harmful to the chickens. They varied widely in size, shape, colour, reflectance, texture, weight, odour, acoustic qualities, deformability, displaceability and destructibility. For example, among the objects were a wooden chair, a beach ball, a tin of marbles, a mirror, a rubber boot, a bamboo stalk and a tray of sand. Most objects were placed on the floor but some were suspended from the ceiling and others were presented in novel containers. They were predicted to stimulate inspective exploration ŽBerlyne, 1960. to a greater extent than the supplementary resources treatment. Some stimulation of foraging, locomotory and dust bathing behaviour was also anticipated, depending on the items provided each day. 2.3. Data collection To assess use of the different peripheral areas, an instantaneous scan sample was obtained of the number of chickens present in each peripheral area at 1030, 1130 and 1230 h on four consecutive days each week, between 8 and 39 days. All birds with their head and at least half their body across the gateway into the peripheral area were counted. To obtain an estimate of the level of chicken interaction with the novel objects and the supplementary resources, it was noted during each scan whether or not there was at least one bird with his head within two bird lengths of each of the three stimuli. To examine the pattern of bird movement back and forth between the peripheral and home areas during the 3-h period when the gate was open, 3 h video recordings were made of activity through the gateway between 36 and 39 days. From the videos, counts
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were made of the number of birds going in and out of the peripheral area during each 5-min period while the gate was opened. Thirty to 40 randomly selected chickens per pen were weighed at 21 and 42 days. Consumption of the starter and grower diets was measured and feed conversion efficiency was calculated. Dead birds were necropsied to determine cause of death. 2.4. Statistical analysis Proportions were transformed by arc sine where necessary to conform to assumptions of parametric statistics. Treatment effects on the proportion of birds in the peripheral area, pen mean body weight, feed efficiency and mortality were analysed using the General Linear Model of the SAS Institute Ž1989.. Repeated measures analyses were performed to assess age and time of day effects on use of the peripheral area. Chi-squared Ž x 2 . tests were used to examine treatment effects on movements in and out of the peripheral area.
3. Results Use of the peripheral area differed significantly between treatments Ž F3,12 s 27.3, P - 0.001.. Chickens on the essential resources treatment used the peripheral area significantly more than chickens on the supplementary resources and novel objects treatments, and these chickens used the area significantly more than chickens on the empty treatment ŽRyan–Einot–Gabriel–Welsch multiple range test, P - 0.05.. Age also had a strongly significant effect on use of the peripheral area Ž F4,48 s 73.5, P - 0.001., with use increasing to a peak in week 5 and dropping slightly in week 6. The shape of the age curve was defined by linear Ž F1,48 s 204.8, P - 0.001., quadratic Ž F1,48 s 66.7, P - 0.001., cubic Ž F1,48 s 15.9, P - 0.001. and quartic Ž F1,48 s 6.7, P s 0.013. components. The effect of age differed between treatments Ž F12,48 s 3.0, P s 0.004., with use of the peripheral area containing essential resources rising more rapidly and peaking earlier than use of areas containing no resources, novel objects or supplementary resources ŽFig. 1.. A separate analysis of use of the peripheral area on the first four days when the area was made accessible Ž8, 9, 10 and 11 days. indicated that the treatment differences were consistent with those of the experiment as a whole Ž F3,12 s 3.5, P s 0.049.. There was a strong linear increase in use of the peripheral area over the first four days in all treatments Ž F1,12 s 284.9, P - 0.001., and no interaction between treatment and age effects during this period Ž F9,36 s 1.7, P s 0.12.. Use of the peripheral area did not vary across the three daily scan times Ž F2,152 s 1.9, P s 0.16. and treatment effects were not significantly influenced by the three daily scan times Ž F6,152 s 2.0, P s 0.07.. The first of these daily scans was made 45 min after opening of the gate. It was observed that, from week 3 onwards, many chickens ran into the peripheral area as soon as the gate was opened although the birds were not visibly congregating by the gate prior to its being opened. Chickens ran towards the gate from
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Fig. 1. Percentage of chickens in the peripheral area during instantaneous scan samples at hourly intervals during the 3-h daily access period Žmean"SEM; ns100 chickens..
all directions, often with wings flapping, and continued running at least 2 m into the peripheral area. The continuous video recordings made during week 6 indicated that, in the first 5 min, more birds on the novel objects treatment entered the peripheral area than did birds on the other treatments Ž77.2% of birds, vs. 43.6, 50.0 and 39.2% of birds on the empty, essential resources and supplementary resources treatments, respectively; x 2 s 30.2, df s 1, P - 0.001.. More birds on the novel objects treatment also left the peripheral area during the first 5 min than birds on the other treatments Ž13.0% of birds, vs. 5.3, 10.4 and 2.1% of birds, respectively; x 2 s 5.1, df s 1, P - 0.05.. In subsequent 5-min periods, there was much less traffic through the gateway and there were no significant treatment effects on mean proportions of birds entering Ž3.4%, x 2 s 2.0, df s 3, P ) 0.05. or leaving Ž3.5%, x 2 s 2.0, df s 3, P ) 0.05. the peripheral area. In the supplementary resources treatment, the mean proportion Ž"SE. of the three daily scans in which there was at least one bird within two bird lengths of each resource increased rapidly with age Ž62 " 6.0% of scans in week 2, 92 " 2.4% in week 3, 97 " 1.6% in week 4 and 100% in weeks 5 and 6; F4,15 s 45.6, P - 0.001.. A similar but slower increase with age occurred with respect to bird proximity to the three novel objects in the novel objects treatment Ž38 " 7.7% of scans in week 2, 83 " 2.5% in week 3, 85 " 3.5% in week 4, 90 " 3.1% in week 5 and 94 " 2.0% in week 6; F4,15 s 34.3, P - 0.001.. Chickens on the essential resources treatment consumed an average of 11 " 0.6% of their total feed intake in the peripheral area between 8 and 21 days, and 12 " 0.2% between 22 and 41 days. Chicken body weights did not differ significantly between treatments at 21 days Žmean " SE, 0.80 " 0.003 kg. or 42 days Ž2.49 " 0.008 kg, F3,12 F 0.6, P ) 0.05.. Feed efficiency from hatch to 42 days was similar between treatments Ž0.59 " 0.007, F3,12 s
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1.0, P ) 0.05.. The mortality rate from hatch to 42 days did not vary between treatments Ž6.3 " 0.67%, F3,12 s 1.8, P ) 0.05. and there were no significant treatment effects on the most common causes of mortality, including sudden death syndrome Ž3.9 " 0.47%., ascites Ž0.5 " 0.16%. and leg deformities Ž0.3 " 0.12%, F3,12 F 1.0, P ) 0.05..
4. Discussion Chickens on all treatments readily made use of space that was intermittently accessible. Such behaviour could result from physical restriction of movement in the home area or insufficient access to essential resources. Nicol Ž1987. reported that hens performed ‘rebound’ levels of wing flapping, tail wagging and stretching in a somewhat larger space Ž2310 cm2 . after confinement for several weeks in a very restricted space Ž847 cm2 .. However, in the current study, the chickens were confined in a relatively spacious home area that did not physically restrict their ability to move. Although chickens deprived of food or litter exhibit elevated levels of extrinsic exploration ŽNicol and Guildford, 1991., the chickens in this study were not deprived of essential resources in their home area. Water and nutritionally complete food were available at all times and the housing enclosure provided protection from predators, parasites and climatic extremes. Survival and growth were not enhanced by the provision of essential resources in the peripheral area. Therefore, neither physical restriction of movement nor inadequate access to essential resources in the home area can explain use of the peripheral area. Although data for determination of behavioural time budgets were not collected in this experiment, chickens on the supplementary resources treatment were observed dust bathing in the peat moss in the peripheral area whereas only wood shavings were available as a substrate for dust bathing in the home area. Peat moss is greatly preferred over wood shavings as a dust bathing substrate ŽPetherick and Duncan, 1989. as well as being a more effective substrate for cleaning the feathers and improving their insulative value ŽVan Liere, 1991.. Chickens were also observed hopping, standing and sitting on the straw bale Žbut rarely on the wooden platform. whereas they were confined to the floor in the home area. They pecked and scratched in the straw and the peat moss, materials unavailable in the home area. These opportunities probably contributed to the higher use of the peripheral area in this treatment than in the empty treatment. On average, 47.5 " 2.88% of the chickens on this treatment were present in the peripheral area on any one scan indicating that the chickens were not, in general, spending the full 3 h in the peripheral area. In week 6, they were no more highly motivated to enter the peripheral area during the first 5 min than chickens on the empty or essential resources treatments, suggesting that the chickens were not suffering from the absence of supplementary resources in the home area. Use of the peripheral area was greatest on the essential resources treatment. Presumably, after arrival in the peripheral area, chickens on this treatment were more likely to stay there than chickens on the other treatments because they had no need to return to the home area for essential resources. During weeks 4 and 5, significantly more than 50% of the chickens on this treatment were in the peripheral area on any one scan Žmean
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75.2%, x 2 s 12.72, df s 1, P - 0.005. contrary to the ideal free Žequal. distribution predicted when two areas provide identical but limited resources to a group of equal competitors ŽMilinski and Parker, 1991.. Broiler chickens can be considered equal competitors in that their movements are not constrained by dominance relationships ŽEstevez et al., 1997.. The uneven distribution of the birds between the home and peripheral areas suggests that the birds placed higher value on being in the less used area due to its greater novelty. They may also have preferred to scratch in the cleaner litter of the peripheral area. The relatively low use of the empty area may have been influenced by the relative lack of cover in this area. Chickens spend more time in areas with vertical cover than in open areas and are more likely to perform vulnerable activities, such as resting and preening, in the vicinity of cover ŽNewberry and Shackleton, 1997.. Lack of cover as well as brooder heat could have motivated chickens to return to the home area to rest after a period of activity in the peripheral area. In week 6, movement into the peripheral area during the first 5 min after gate opening was significantly greater on the novel objects treatment than on the other treatments suggesting that the chickens were actively seeking novelty. Although the wire fence between the home and peripheral areas did not obstruct vision, the closest object was about 1.5 m from the fence. The chickens would not have been able to inspect the novel objects effectively from the home area because they must be within 30 cm of a visual stimulus to discriminate fine details ŽDawkins, 1996.. Also, enhancement of brain development in an enriched environment is dependent upon active interaction with novel objects. Passive exposure to novel objects on the other side of a fence does not have this effect ŽFerchmin et al., 1975.. The finding that more birds on this treatment left the peripheral area during the first 5 min than in the other treatments may have been associated with elevated arousal Žfear. associated with the higher level of novelty. The rapid entrance into the peripheral area on all treatments and the elevated use of areas containing novel objects are consistent with the hypothesis that chickens have an intrinsic motivation ŽBerlyne, 1960; Wood-Gush and Vestergaard, 1991. to seek opportunities to perform exploratory behaviour Ži.e., exploring for its own sake rather than searching for currently needed resources. and that this motivation is not satisfied when chickens are kept in a relatively constant environment. From an evolutionary perspective, there are reasons why chickens should be genetically predisposed to anticipate and seek changes through exploratory behaviour in the peripheral area. Animals detect changes in the characteristics and layout of environmental features as evidenced by increased exploratory investigation of altered features ŽBerlyne, 1960; Thinus-Blanc et al., 1987.. Through periodic visits to different areas of a territory or home range Žpatrolling behaviour., renewed food patches may be discovered and changes in physical structure Že.g., due to vegetative growth, wind damage, flooding, etc.. and in the presence of predators and territorial intruders can be monitored. The cognitive map ŽPoucet, 1993. of the spatial layout of food patches, refuges, escape routes, territory neighbours and other features of the home range can be updated and this knowledge can be integrated with motor learning ŽStamps, 1995.. From a proximate perspective, the speed of entry into the peripheral area when the gate was opened suggests that the chickens may have experienced boredom in the home
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area due to deprivation of opportunities to perform exploratory behaviour. The home areas were smaller Ž21.5 m2 . than the weekly home range sizes reported previously for male chickens living in a 407 m2 pen Žminimum polygon area, week 4, 142 m2 ; week 5, 128 m2 ; week 6, 84 m2 ; Newberry and Hall, 1990.. With continuous exposure to the home area over time, the chickens would have habituated to the majority of stimuli in that environment, given that the stimuli were unchanging and had no positive or negative impact on the birds. Opportunities for exploration Žinteraction with novel stimuli., thus, declined over time with increasing familiarity with the home area. If the motivation to enter a less used area increased with increasing exposure to the home environment, it could explain the initial rapid entry into the peripheral area when the gate was opened and the increased use of this area with increasing age on all treatments. Competition for resources could also explain the chickens’ tendency to run into an intermittently available space. Although the essential and supplementary resources were unlimited while the gate was opened, it is possible that the chickens continued to behave as if resources were limited even if they were abundant on previous visits. The competition hypothesis does not, however, explain the finding that chickens on the novel objects treatment were the most motivated to enter the peripheral area rapidly when the gate opened. The novel objects did not have any obvious resource value to the chickens and it is unlikely that chickens would compete more for access to novel objects than for essential or supplementary resources. If they did not differentiate between the types of resources they would find in the peripheral area, it is unclear why the rate of entry to this area would differ between treatments. Increased use of the peripheral area with increasing age may have been reinforced by the weekly increase in photoperiod, resulting in longer periods of exposure to visual stimuli in the home area. The increasing photoperiod also provided increased time for the performance of essential activities such as feeding, thereby reducing time constraints on the performance of less urgent behaviour ŽDawkins, 1983. such as intrinsic exploration. The increased energetic cost of entering the peripheral area as the birds neared market weight coupled with the increasing familiarity with that area Žpossibly resulting in improved patrolling efficiency. could have contributed to the slight decline in use during week 6. It is also possible that, during ontogeny, exploratory motivation declines after about 4 to 5 weeks of age. Newberry and Hall Ž1990. suggested that leg disorders may have contributed to a decline in use of space by male broiler chickens from 4 to 9 weeks of age. In the current study, the rapid movement of chickens into the peripheral area during week 6, and the relatively low mortality due to leg disorders, suggest that skeletal disease was not a major factor contributing to reduced use of the peripheral area in week 6. In conclusion, chickens on all treatments were motivated to enter the peripheral area. The data on number of chickens entering the area during the first 5 min suggest that this motivation was elevated when the area contained novel objects. Overall use of the peripheral area was greater on the novel objects treatment than the empty treatment, and similar to the supplementary resources treatment, despite a relative lack of immediately useful resources. The results support the hypothesis that broiler chickens are motivated to seek opportunities to explore novel stimuli. Survival to 6 weeks of age, final body weight and overall feed efficiency did not vary according to the resources provided in
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the peripheral area. Given the strong artificial selection pressure for high productivity, treatment differences in the overall use of the peripheral area suggest that the chickens adjusted their time in the peripheral area according to its net value for maximising production traits. Not surprisingly, the chickens placed priority on access to essential resources. The results show that space containing novel objects or supplementary resources was of greater value to the chickens than empty space and that these stimuli could be provided with no adverse effects on production traits. Acknowledgements I am grateful to L. Struthers, K. Ingram and H. Hanson for assistance with animal care and data collection. Funding was provided by the British Columbia Chicken Marketing Board and Agriculture and Agri-Food Canada. S. Cloutier provided helpful comments on an earlier draft. References Ambrose, H.W., 1972. Effect of habitat familiarity and toe-clipping on rate of owl predation in Microtus pennsylÕanicus. J. Mammal. 53, 909–912. Berlyne, D.E., 1960. Conflict, Arousal, and Curiosity. McGraw-Hill, New York, 350 pp. Blair, R., Newberry, R.C., Gardiner, E.E., 1993. Effects of lighting pattern and dietary tryptophan supplementation on growth and mortality in broilers. Poultry Sci. 72, 495–502. Classen, H.L., Riddell, C., Robinson, F.E., 1991. Effects of increasing photoperiod length on performance and health of broilers. Br. Poult. Sci. 32, 21–29. Collias, N.E., Collias, E.C., 1967. A field study of the red jungle fowl in north-central India. Condor 69, 360–386. Dawkins, M.S., 1983. Battery hens name their price: consumer demand theory and the measurement of ethological ‘needs’. Anim. Behav. 20, 209–225. Dawkins, M.S., 1996. Distance and social recognition in hens: implications for the use of photographs as social stimuli. Behaviour 133, 663–680. Estevez, I., Newberry, R.C., Arias de Reyna, L., 1997. Broiler chickens: a tolerant social system?. Etologia 5, 19–29. Ferchmin, P.A., Bennett, E.L., Rosenzweig, M.R., 1975. Direct contact with enriched environment is required to alter cerebral weights in rats. J. Comp. Physiol. Psychol. 88, 360–367. Kolb, B., Whitshaw, I.Q., 1998. Brain plasticity and behaviour. Annu. Rev. Psychol. 49, 43–64. Humphrey, N.K., 1976. The social function of intellect. In: Bateson, P.P.G., Hinde, R.A. ŽEds.., Growing Points in Ethology. Cambridge Univ. Press, Cambridge, pp. 303–317. Mather, J.A., 1995. Cognition in cephalopods. Adv. Study Behav. 24, 317–353. McBride, G., Parer, I.P., Foenander, F., 1969. The social organisation and behaviour of the feral domestic fowl. Anim. Behav. Monogr. 2, 127–181. Mench, J.A., 1998. Environmental enrichment and the importance of exploratory behaviour. In: Shepherdson, D.J., Mellen, J.D., Hutchins, M. ŽEds.., Second Nature Environmental Enrichment for Captive Animals. Smithsonian Institution Press, Washington, DC, pp. 30–46. Milinski, M., Parker, G.A., 1991. Competition for resources. In: Krebs, J.R., Davies, N.B. ŽEds.., Behavioural Ecology An Evolutionary Approach. Blackwell, Oxford, pp. 137–168. Murphy, L.B., Wood-Gush, D.G.M., 1978. The interpretation of the behaviour of domestic fowl in strange environments. Biol. Behav. 3, 39–61. Newberry, R.C., 1995. Environmental enrichment: increasing the biological relevance of captive environments. Appl. Anim. Behav. Sci. 44, 229–243.
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Newberry, R.C., Hall, J.W., 1990. Use of pen space by broiler chickens: effects of age and pen size. Appl. Anim. Behav. Sci. 25, 125–136. Newberry, R.C., Shackleton, D.M., 1997. Use of visual cover by domestic fowl: a Venetian blind effect?. Anim. Behav. 54, 387–395. Nicol, C.J., 1987. Behavioural responses of laying hens following a period of spatial restriction. Anim. Behav. 35, 1709–1719. Nicol, C.J., Guildford, T., 1991. Exploratory activity as a measure of motivation in deprived hens. Anim. Behav. 41, 333–341. Petherick, J.C., Duncan, I.J.H., 1989. Behaviour of young domestic fowl directed towards different substrates. Br. Poult. Sci. 30, 229–238. Poucet, B., 1993. Spatial cognitive maps in animals: new hypotheses on their structure and neural mechanisms. Psychol. Rev. 100, 163–182. Renner, M.J., Rosenzweig, M.R., 1987. Enriched and Impoverished Environments Effects on Brain and Behaviour. Springer, New York, 134 pp. SAS Institute, 1989. User’s Guide, Version 6, 4th edn. SAS Institute, Cary, NC, USA. Stamps, J., 1995. Motor learning and the value of familiar space. Am. Nat. 146, 41–58. Thinus-Blanc, C., Bouzouba, L., Chaiz, K., Chapuis, N., Durup, M., Poucet, B., 1987. A study of spatial parameters encoded during exploration in hamsters. J. Exp. Psychol. Anim. Behav. Proc. 13, 418–427. Van Liere, D.W., 1991. Function and organisation of dustbathing in laying hens. PhD Thesis. Agricultural University, Wageningen, The Netherlands. Welker, W.I., 1957. ‘Free’ vs. ‘forced’ exploration of a novel situation by rats. Psychological Reports 3, 95–108. Wemelsfelder, F., Birke, L., 1997. Environmental challenge. In: Appleby, M.C., Hughes, B.O. ŽEds.., Animal Welfare. CAB International, Wallingford, UK, pp. 35–47. Wood-Gush, D.G.M., Vestergaard, K., 1991. The seeking of novelty and its relation to play. Anim. Behav. 42, 599–606.
Exploratory behaviour of young domestic fowl Ruth C. Newberry
a,b,)
a
Center for the Study of Animal Well-being, Department of Animal Sciences, Washington State UniÕersity, Pullman, WA 99164-6520, USA b Department of Veterinary and ComparatiÕe Anatomy, Pharmacology and Physiology, Washington State UniÕersity, Pullman, WA 99164-6520, USA Accepted 3 February 1999
Abstract Under the hypothesis that young domestic fowl, Gallus gallus, are motivated to seek opportunities to explore novel stimuli, it was predicted that broiler chickens would show greater motivation to enter peripheral space if it contained Ža. novel objects Žchanged daily. than if it was Žb. empty or contained Žc. essential resources Žfood, water, heat. or Žd. supplementary resources Žpeat moss, straw bale, elevated platform.. Sixteen pens, each containing 100 chickens, were set up with a home area containing essential resources and an adjacent peripheral area of the same size to which the chickens were allowed access for 3 h daily by opening a gate. There were four replicate pens on each of four treatments varying in the resources Ža–d. provided in the peripheral area. During week 6, continuous video recordings showed that more chickens on the novel objects treatment ran into the peripheral area during the first 5 min after the gates were opened than did chickens on the other three treatments Ž P - 0.001.. From weeks 2 to 6, scan samples at hourly intervals while the gates were open indicated that, on average, the number of chickens in the peripheral area was significantly higher on the essential resources treatment, and significantly lower on the empty treatment, than on the novel objects and supplementary resources treatments. Chicken survival, body weight and feed efficiency did not differ between treatments Ž P ) 0.05.. The results support the hypothesis that the chickens were motivated to seek opportunities to explore novel stimuli. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Broiler chicken; Exploration; Boredom; Environmental enrichment; Use of space; Animal welfare
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Tel.: q1-509-335-2957; fax: q1-509-335-4650; e-mail: [email protected]
0168-1591r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 1 5 9 1 Ž 9 9 . 0 0 0 1 6 - 7
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1. Introduction Young domestic fowl, Gallus gallus domesticus, being intensively reared for meat are typically kept indoors in flocks of several thousand chickens on a litter-covered floor. Sources of food, water and supplementary heat are distributed abundantly and predictably throughout the available space so that travel time, search time and competition for resources are minimised. In countries with cold winters, chicken houses are usually windowless and provided with low intensity lighting. The ambient temperature is lowered gradually as the chickens grow and temperature fluctuations are controlled within narrow limits. Most broiler chickens are uniformly white-feathered, and kept in flocks of the same age and genetic background. These conditions differ sharply from the conditions experienced by chickens during their evolutionary history. It is only within the last 50 years that chickens have been confined indoors for intensive production. Prior to this time, they were exposed to a variety of vegetation, predators, prey, weather conditions and seasonal changes ŽCollias and Collias, 1967; McBride et al., 1969.. Under these conditions, learning has survival value ŽAmbrose, 1972; Stamps, 1995.. During their evolutionary history, domestic fowl have had life history characteristics associated with the evolution of intellect, including life in stable social groups with overlapping generations ŽHumphrey, 1976., central place foraging and exploitation of a wide variety of prey ŽMather, 1995; Mench, 1998.. There is ample evidence of brain plasticity associated with learning in the domestic fowl ŽKolb and Whitshaw, 1998.. Exploratory behaviour involves information gathering through active interaction with novel stimuli in the environment ŽBerlyne, 1960.. Boredom results from a chronic lack of opportunities for active interaction with the environment ŽWemelsfelder and Birke, 1997.. The housing of broiler chickens in a relatively constant environment throughout their lifetime raises the question of whether the chickens’ well-being is compromised by boredom. After an initial period of exploration, chickens will habituate to stimuli in their housing environment that have no perceived positive or detrimental effects. In the absence of new sources of novelty, the environment becomes highly predictable and the chickens may no longer be stimulated to perform exploratory behaviour. If so, the lack of novelty may be associated with impaired brain development ŽRenner and Rosenzweig, 1987. and boredom. Although chickens exhibit fear-related behaviour when novelty is encountered in open field tests ŽMurphy and Wood-Gush, 1978., these tests involve placing animals in a novel environment, usually alone, and without refuges or escape routes ŽWelker, 1957.. When chickens are able to control their exposure to novelty through voluntary approach and retreat, a higher level of exploratory investigation is predicted. The present experiment examined whether broiler chickens would voluntarily enter areas that provided opportunities for interaction with stimuli not found in a typical broiler chicken house. Such behaviour could point out inadequacies in the typical housing environment that may impact upon the well-being of broiler chickens. Chickens were given voluntary access to areas containing either Ža. no resources, Žb. essential resources that were also present in the home environment, Žc. novel objects, or Žd. supplementary resources considered to have biological value to the chickens and not
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available in the home environment. It was hypothesised that broiler chickens are motivated to seek opportunities to explore novel stimuli. According to this hypothesis, it was predicted that the chickens would be more motivated to enter a peripheral area if it contained novel objects than if the area contained no resources, essential resources or supplementary resources.
2. Methods 2.1. Animals and husbandry Sixteen floor pens were set up in a light-tight, insulated chicken house. The fences between each pen were covered with a black plastic visual barrier. A 4.3-m long transparent wire mesh partition divided each pen into two halves, each measuring 4.3 m = 5.0 m. The partition contained a 1.5-m long wire mesh gate at one end. One half of the pen was designated as the home area, and the other half as the peripheral area. All home areas were furnished identically with a gas brooder Ž1.2 m diameter. in the centre of the area, a water trough Ž234 cm long. on either side of the brooder and a tube feeder Žpan diameter 35.6 cm, 1–19 days; 41.9 cm, 20–42 days. in each corner. A 5-cm deep layer of fresh softwood shavings was spread over both halves of each pen. A total of 1600 male Peterson= Arbor Acre chicks, vaccinated against Marek’s disease, were obtained from a commercial hatchery. One hundred randomly selected chicks were placed in each of the 16 home areas. The chicks were kept in a corral under the brooder until day 7, when the corrals were removed. From 8 to 41 days, with the exception of day 21, the gates were opened to give all chickens access to the other half of their pen Žperipheral area. from 0945 to 1245 h daily. All chickens were fed a 23% protein starter diet from 0 to 21 days and a 20% protein grower diet from 21 to 42 days. Food and water were provided ad libitum. Light intensity was 20 lx, 0–6 days and 5 lx, 7–42 days, as measured 23 cm above the litter, directly beneath the two 100 W–130 V frosted incandescent light bulbs per pen. An increasing photoperiod lighting program Ž23L:1D, 0–3 days; 6L:18D, 4–14 days; 10L:14D, 15–21 days; 14L:10D, 22–28 days; 18L:6D, 29–35 days, 23L:1D, 36–42 days. was used to minimise mortality and leg disorders ŽClassen et al., 1991; Blair et al., 1993.. The photoperiod started at 0730 h daily. Temperature under the brooders was reduced by 28C weekly, from 318C at 1 day to 218C at 35 days. 2.2. Experiment treatments The peripheral area of each pen was assigned to one of four treatments. Each treatment was replicated in four pens in a randomised block design. The stimuli provided in each treatment were in place from 1 to 41 days. Chickens, thus, had the opportunity to become familiar with the view of the peripheral area before the gates were opened for the first time at 8 days.
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In the ‘empty’ treatment, the peripheral area was an empty space with no furnishings or resources apart from wood shavings on the floor Žalso present in all other peripheral and home areas.. In the ‘essential resources’ treatment, the peripheral area contained four feeders, two water troughs and a gas brooder in the same layout, and operated in the same manner, as in the home area. In the ‘supplementary resources’ treatment, the peripheral area was equipped with Ža. a bale of wheat straw Žbaler twine removed., Žb. a wooden platform Ž1 m L = 1 m W = 30 cm H, with wire mesh to prevent chickens from going underneath. with a wooden ramp Ž1 m L = 10 cm W = 2 cm D . attached to the centre of one side, and Žc. a wooden platform without wire mesh, turned upside down Žwalls 10 cm high. and kept filled with peat moss. These items were not available in the home area and were expected to have biological relevance to the chickens ŽNewberry, 1995. by stimulating foraging behaviour Žpecking, scratching, manipulating., locomotory behaviour Žclimbing, jumping, flying., and dust bathing, respectively. The straw bale, wooden platform and peat moss box were arranged approximately 2 m apart in a triangle, in the centre of the peripheral area, with the point of the triangle towards the central partition between the home and peripheral areas. In the ‘novel objects’ treatment, three novel objects were placed in the peripheral area on day 1 in the same triangular layout as in the supplementary resources treatment. From 2 to 41 days, the novel objects were replaced daily between 0800 h and 0900 h. Each set of three objects was used only once in each pen. The objects Ž n s 123. were non-nutritive and non-harmful to the chickens. They varied widely in size, shape, colour, reflectance, texture, weight, odour, acoustic qualities, deformability, displaceability and destructibility. For example, among the objects were a wooden chair, a beach ball, a tin of marbles, a mirror, a rubber boot, a bamboo stalk and a tray of sand. Most objects were placed on the floor but some were suspended from the ceiling and others were presented in novel containers. They were predicted to stimulate inspective exploration ŽBerlyne, 1960. to a greater extent than the supplementary resources treatment. Some stimulation of foraging, locomotory and dust bathing behaviour was also anticipated, depending on the items provided each day. 2.3. Data collection To assess use of the different peripheral areas, an instantaneous scan sample was obtained of the number of chickens present in each peripheral area at 1030, 1130 and 1230 h on four consecutive days each week, between 8 and 39 days. All birds with their head and at least half their body across the gateway into the peripheral area were counted. To obtain an estimate of the level of chicken interaction with the novel objects and the supplementary resources, it was noted during each scan whether or not there was at least one bird with his head within two bird lengths of each of the three stimuli. To examine the pattern of bird movement back and forth between the peripheral and home areas during the 3-h period when the gate was open, 3 h video recordings were made of activity through the gateway between 36 and 39 days. From the videos, counts
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were made of the number of birds going in and out of the peripheral area during each 5-min period while the gate was opened. Thirty to 40 randomly selected chickens per pen were weighed at 21 and 42 days. Consumption of the starter and grower diets was measured and feed conversion efficiency was calculated. Dead birds were necropsied to determine cause of death. 2.4. Statistical analysis Proportions were transformed by arc sine where necessary to conform to assumptions of parametric statistics. Treatment effects on the proportion of birds in the peripheral area, pen mean body weight, feed efficiency and mortality were analysed using the General Linear Model of the SAS Institute Ž1989.. Repeated measures analyses were performed to assess age and time of day effects on use of the peripheral area. Chi-squared Ž x 2 . tests were used to examine treatment effects on movements in and out of the peripheral area.
3. Results Use of the peripheral area differed significantly between treatments Ž F3,12 s 27.3, P - 0.001.. Chickens on the essential resources treatment used the peripheral area significantly more than chickens on the supplementary resources and novel objects treatments, and these chickens used the area significantly more than chickens on the empty treatment ŽRyan–Einot–Gabriel–Welsch multiple range test, P - 0.05.. Age also had a strongly significant effect on use of the peripheral area Ž F4,48 s 73.5, P - 0.001., with use increasing to a peak in week 5 and dropping slightly in week 6. The shape of the age curve was defined by linear Ž F1,48 s 204.8, P - 0.001., quadratic Ž F1,48 s 66.7, P - 0.001., cubic Ž F1,48 s 15.9, P - 0.001. and quartic Ž F1,48 s 6.7, P s 0.013. components. The effect of age differed between treatments Ž F12,48 s 3.0, P s 0.004., with use of the peripheral area containing essential resources rising more rapidly and peaking earlier than use of areas containing no resources, novel objects or supplementary resources ŽFig. 1.. A separate analysis of use of the peripheral area on the first four days when the area was made accessible Ž8, 9, 10 and 11 days. indicated that the treatment differences were consistent with those of the experiment as a whole Ž F3,12 s 3.5, P s 0.049.. There was a strong linear increase in use of the peripheral area over the first four days in all treatments Ž F1,12 s 284.9, P - 0.001., and no interaction between treatment and age effects during this period Ž F9,36 s 1.7, P s 0.12.. Use of the peripheral area did not vary across the three daily scan times Ž F2,152 s 1.9, P s 0.16. and treatment effects were not significantly influenced by the three daily scan times Ž F6,152 s 2.0, P s 0.07.. The first of these daily scans was made 45 min after opening of the gate. It was observed that, from week 3 onwards, many chickens ran into the peripheral area as soon as the gate was opened although the birds were not visibly congregating by the gate prior to its being opened. Chickens ran towards the gate from
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Fig. 1. Percentage of chickens in the peripheral area during instantaneous scan samples at hourly intervals during the 3-h daily access period Žmean"SEM; ns100 chickens..
all directions, often with wings flapping, and continued running at least 2 m into the peripheral area. The continuous video recordings made during week 6 indicated that, in the first 5 min, more birds on the novel objects treatment entered the peripheral area than did birds on the other treatments Ž77.2% of birds, vs. 43.6, 50.0 and 39.2% of birds on the empty, essential resources and supplementary resources treatments, respectively; x 2 s 30.2, df s 1, P - 0.001.. More birds on the novel objects treatment also left the peripheral area during the first 5 min than birds on the other treatments Ž13.0% of birds, vs. 5.3, 10.4 and 2.1% of birds, respectively; x 2 s 5.1, df s 1, P - 0.05.. In subsequent 5-min periods, there was much less traffic through the gateway and there were no significant treatment effects on mean proportions of birds entering Ž3.4%, x 2 s 2.0, df s 3, P ) 0.05. or leaving Ž3.5%, x 2 s 2.0, df s 3, P ) 0.05. the peripheral area. In the supplementary resources treatment, the mean proportion Ž"SE. of the three daily scans in which there was at least one bird within two bird lengths of each resource increased rapidly with age Ž62 " 6.0% of scans in week 2, 92 " 2.4% in week 3, 97 " 1.6% in week 4 and 100% in weeks 5 and 6; F4,15 s 45.6, P - 0.001.. A similar but slower increase with age occurred with respect to bird proximity to the three novel objects in the novel objects treatment Ž38 " 7.7% of scans in week 2, 83 " 2.5% in week 3, 85 " 3.5% in week 4, 90 " 3.1% in week 5 and 94 " 2.0% in week 6; F4,15 s 34.3, P - 0.001.. Chickens on the essential resources treatment consumed an average of 11 " 0.6% of their total feed intake in the peripheral area between 8 and 21 days, and 12 " 0.2% between 22 and 41 days. Chicken body weights did not differ significantly between treatments at 21 days Žmean " SE, 0.80 " 0.003 kg. or 42 days Ž2.49 " 0.008 kg, F3,12 F 0.6, P ) 0.05.. Feed efficiency from hatch to 42 days was similar between treatments Ž0.59 " 0.007, F3,12 s
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1.0, P ) 0.05.. The mortality rate from hatch to 42 days did not vary between treatments Ž6.3 " 0.67%, F3,12 s 1.8, P ) 0.05. and there were no significant treatment effects on the most common causes of mortality, including sudden death syndrome Ž3.9 " 0.47%., ascites Ž0.5 " 0.16%. and leg deformities Ž0.3 " 0.12%, F3,12 F 1.0, P ) 0.05..
4. Discussion Chickens on all treatments readily made use of space that was intermittently accessible. Such behaviour could result from physical restriction of movement in the home area or insufficient access to essential resources. Nicol Ž1987. reported that hens performed ‘rebound’ levels of wing flapping, tail wagging and stretching in a somewhat larger space Ž2310 cm2 . after confinement for several weeks in a very restricted space Ž847 cm2 .. However, in the current study, the chickens were confined in a relatively spacious home area that did not physically restrict their ability to move. Although chickens deprived of food or litter exhibit elevated levels of extrinsic exploration ŽNicol and Guildford, 1991., the chickens in this study were not deprived of essential resources in their home area. Water and nutritionally complete food were available at all times and the housing enclosure provided protection from predators, parasites and climatic extremes. Survival and growth were not enhanced by the provision of essential resources in the peripheral area. Therefore, neither physical restriction of movement nor inadequate access to essential resources in the home area can explain use of the peripheral area. Although data for determination of behavioural time budgets were not collected in this experiment, chickens on the supplementary resources treatment were observed dust bathing in the peat moss in the peripheral area whereas only wood shavings were available as a substrate for dust bathing in the home area. Peat moss is greatly preferred over wood shavings as a dust bathing substrate ŽPetherick and Duncan, 1989. as well as being a more effective substrate for cleaning the feathers and improving their insulative value ŽVan Liere, 1991.. Chickens were also observed hopping, standing and sitting on the straw bale Žbut rarely on the wooden platform. whereas they were confined to the floor in the home area. They pecked and scratched in the straw and the peat moss, materials unavailable in the home area. These opportunities probably contributed to the higher use of the peripheral area in this treatment than in the empty treatment. On average, 47.5 " 2.88% of the chickens on this treatment were present in the peripheral area on any one scan indicating that the chickens were not, in general, spending the full 3 h in the peripheral area. In week 6, they were no more highly motivated to enter the peripheral area during the first 5 min than chickens on the empty or essential resources treatments, suggesting that the chickens were not suffering from the absence of supplementary resources in the home area. Use of the peripheral area was greatest on the essential resources treatment. Presumably, after arrival in the peripheral area, chickens on this treatment were more likely to stay there than chickens on the other treatments because they had no need to return to the home area for essential resources. During weeks 4 and 5, significantly more than 50% of the chickens on this treatment were in the peripheral area on any one scan Žmean
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75.2%, x 2 s 12.72, df s 1, P - 0.005. contrary to the ideal free Žequal. distribution predicted when two areas provide identical but limited resources to a group of equal competitors ŽMilinski and Parker, 1991.. Broiler chickens can be considered equal competitors in that their movements are not constrained by dominance relationships ŽEstevez et al., 1997.. The uneven distribution of the birds between the home and peripheral areas suggests that the birds placed higher value on being in the less used area due to its greater novelty. They may also have preferred to scratch in the cleaner litter of the peripheral area. The relatively low use of the empty area may have been influenced by the relative lack of cover in this area. Chickens spend more time in areas with vertical cover than in open areas and are more likely to perform vulnerable activities, such as resting and preening, in the vicinity of cover ŽNewberry and Shackleton, 1997.. Lack of cover as well as brooder heat could have motivated chickens to return to the home area to rest after a period of activity in the peripheral area. In week 6, movement into the peripheral area during the first 5 min after gate opening was significantly greater on the novel objects treatment than on the other treatments suggesting that the chickens were actively seeking novelty. Although the wire fence between the home and peripheral areas did not obstruct vision, the closest object was about 1.5 m from the fence. The chickens would not have been able to inspect the novel objects effectively from the home area because they must be within 30 cm of a visual stimulus to discriminate fine details ŽDawkins, 1996.. Also, enhancement of brain development in an enriched environment is dependent upon active interaction with novel objects. Passive exposure to novel objects on the other side of a fence does not have this effect ŽFerchmin et al., 1975.. The finding that more birds on this treatment left the peripheral area during the first 5 min than in the other treatments may have been associated with elevated arousal Žfear. associated with the higher level of novelty. The rapid entrance into the peripheral area on all treatments and the elevated use of areas containing novel objects are consistent with the hypothesis that chickens have an intrinsic motivation ŽBerlyne, 1960; Wood-Gush and Vestergaard, 1991. to seek opportunities to perform exploratory behaviour Ži.e., exploring for its own sake rather than searching for currently needed resources. and that this motivation is not satisfied when chickens are kept in a relatively constant environment. From an evolutionary perspective, there are reasons why chickens should be genetically predisposed to anticipate and seek changes through exploratory behaviour in the peripheral area. Animals detect changes in the characteristics and layout of environmental features as evidenced by increased exploratory investigation of altered features ŽBerlyne, 1960; Thinus-Blanc et al., 1987.. Through periodic visits to different areas of a territory or home range Žpatrolling behaviour., renewed food patches may be discovered and changes in physical structure Že.g., due to vegetative growth, wind damage, flooding, etc.. and in the presence of predators and territorial intruders can be monitored. The cognitive map ŽPoucet, 1993. of the spatial layout of food patches, refuges, escape routes, territory neighbours and other features of the home range can be updated and this knowledge can be integrated with motor learning ŽStamps, 1995.. From a proximate perspective, the speed of entry into the peripheral area when the gate was opened suggests that the chickens may have experienced boredom in the home
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area due to deprivation of opportunities to perform exploratory behaviour. The home areas were smaller Ž21.5 m2 . than the weekly home range sizes reported previously for male chickens living in a 407 m2 pen Žminimum polygon area, week 4, 142 m2 ; week 5, 128 m2 ; week 6, 84 m2 ; Newberry and Hall, 1990.. With continuous exposure to the home area over time, the chickens would have habituated to the majority of stimuli in that environment, given that the stimuli were unchanging and had no positive or negative impact on the birds. Opportunities for exploration Žinteraction with novel stimuli., thus, declined over time with increasing familiarity with the home area. If the motivation to enter a less used area increased with increasing exposure to the home environment, it could explain the initial rapid entry into the peripheral area when the gate was opened and the increased use of this area with increasing age on all treatments. Competition for resources could also explain the chickens’ tendency to run into an intermittently available space. Although the essential and supplementary resources were unlimited while the gate was opened, it is possible that the chickens continued to behave as if resources were limited even if they were abundant on previous visits. The competition hypothesis does not, however, explain the finding that chickens on the novel objects treatment were the most motivated to enter the peripheral area rapidly when the gate opened. The novel objects did not have any obvious resource value to the chickens and it is unlikely that chickens would compete more for access to novel objects than for essential or supplementary resources. If they did not differentiate between the types of resources they would find in the peripheral area, it is unclear why the rate of entry to this area would differ between treatments. Increased use of the peripheral area with increasing age may have been reinforced by the weekly increase in photoperiod, resulting in longer periods of exposure to visual stimuli in the home area. The increasing photoperiod also provided increased time for the performance of essential activities such as feeding, thereby reducing time constraints on the performance of less urgent behaviour ŽDawkins, 1983. such as intrinsic exploration. The increased energetic cost of entering the peripheral area as the birds neared market weight coupled with the increasing familiarity with that area Žpossibly resulting in improved patrolling efficiency. could have contributed to the slight decline in use during week 6. It is also possible that, during ontogeny, exploratory motivation declines after about 4 to 5 weeks of age. Newberry and Hall Ž1990. suggested that leg disorders may have contributed to a decline in use of space by male broiler chickens from 4 to 9 weeks of age. In the current study, the rapid movement of chickens into the peripheral area during week 6, and the relatively low mortality due to leg disorders, suggest that skeletal disease was not a major factor contributing to reduced use of the peripheral area in week 6. In conclusion, chickens on all treatments were motivated to enter the peripheral area. The data on number of chickens entering the area during the first 5 min suggest that this motivation was elevated when the area contained novel objects. Overall use of the peripheral area was greater on the novel objects treatment than the empty treatment, and similar to the supplementary resources treatment, despite a relative lack of immediately useful resources. The results support the hypothesis that broiler chickens are motivated to seek opportunities to explore novel stimuli. Survival to 6 weeks of age, final body weight and overall feed efficiency did not vary according to the resources provided in
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the peripheral area. Given the strong artificial selection pressure for high productivity, treatment differences in the overall use of the peripheral area suggest that the chickens adjusted their time in the peripheral area according to its net value for maximising production traits. Not surprisingly, the chickens placed priority on access to essential resources. The results show that space containing novel objects or supplementary resources was of greater value to the chickens than empty space and that these stimuli could be provided with no adverse effects on production traits. Acknowledgements I am grateful to L. Struthers, K. Ingram and H. Hanson for assistance with animal care and data collection. Funding was provided by the British Columbia Chicken Marketing Board and Agriculture and Agri-Food Canada. S. Cloutier provided helpful comments on an earlier draft. References Ambrose, H.W., 1972. Effect of habitat familiarity and toe-clipping on rate of owl predation in Microtus pennsylÕanicus. J. Mammal. 53, 909–912. Berlyne, D.E., 1960. Conflict, Arousal, and Curiosity. McGraw-Hill, New York, 350 pp. Blair, R., Newberry, R.C., Gardiner, E.E., 1993. Effects of lighting pattern and dietary tryptophan supplementation on growth and mortality in broilers. Poultry Sci. 72, 495–502. Classen, H.L., Riddell, C., Robinson, F.E., 1991. Effects of increasing photoperiod length on performance and health of broilers. Br. Poult. Sci. 32, 21–29. Collias, N.E., Collias, E.C., 1967. A field study of the red jungle fowl in north-central India. Condor 69, 360–386. Dawkins, M.S., 1983. Battery hens name their price: consumer demand theory and the measurement of ethological ‘needs’. Anim. Behav. 20, 209–225. Dawkins, M.S., 1996. Distance and social recognition in hens: implications for the use of photographs as social stimuli. Behaviour 133, 663–680. Estevez, I., Newberry, R.C., Arias de Reyna, L., 1997. Broiler chickens: a tolerant social system?. Etologia 5, 19–29. Ferchmin, P.A., Bennett, E.L., Rosenzweig, M.R., 1975. Direct contact with enriched environment is required to alter cerebral weights in rats. J. Comp. Physiol. Psychol. 88, 360–367. Kolb, B., Whitshaw, I.Q., 1998. Brain plasticity and behaviour. Annu. Rev. Psychol. 49, 43–64. Humphrey, N.K., 1976. The social function of intellect. In: Bateson, P.P.G., Hinde, R.A. ŽEds.., Growing Points in Ethology. Cambridge Univ. Press, Cambridge, pp. 303–317. Mather, J.A., 1995. Cognition in cephalopods. Adv. Study Behav. 24, 317–353. McBride, G., Parer, I.P., Foenander, F., 1969. The social organisation and behaviour of the feral domestic fowl. Anim. Behav. Monogr. 2, 127–181. Mench, J.A., 1998. Environmental enrichment and the importance of exploratory behaviour. In: Shepherdson, D.J., Mellen, J.D., Hutchins, M. ŽEds.., Second Nature Environmental Enrichment for Captive Animals. Smithsonian Institution Press, Washington, DC, pp. 30–46. Milinski, M., Parker, G.A., 1991. Competition for resources. In: Krebs, J.R., Davies, N.B. ŽEds.., Behavioural Ecology An Evolutionary Approach. Blackwell, Oxford, pp. 137–168. Murphy, L.B., Wood-Gush, D.G.M., 1978. The interpretation of the behaviour of domestic fowl in strange environments. Biol. Behav. 3, 39–61. Newberry, R.C., 1995. Environmental enrichment: increasing the biological relevance of captive environments. Appl. Anim. Behav. Sci. 44, 229–243.
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Newberry, R.C., Hall, J.W., 1990. Use of pen space by broiler chickens: effects of age and pen size. Appl. Anim. Behav. Sci. 25, 125–136. Newberry, R.C., Shackleton, D.M., 1997. Use of visual cover by domestic fowl: a Venetian blind effect?. Anim. Behav. 54, 387–395. Nicol, C.J., 1987. Behavioural responses of laying hens following a period of spatial restriction. Anim. Behav. 35, 1709–1719. Nicol, C.J., Guildford, T., 1991. Exploratory activity as a measure of motivation in deprived hens. Anim. Behav. 41, 333–341. Petherick, J.C., Duncan, I.J.H., 1989. Behaviour of young domestic fowl directed towards different substrates. Br. Poult. Sci. 30, 229–238. Poucet, B., 1993. Spatial cognitive maps in animals: new hypotheses on their structure and neural mechanisms. Psychol. Rev. 100, 163–182. Renner, M.J., Rosenzweig, M.R., 1987. Enriched and Impoverished Environments Effects on Brain and Behaviour. Springer, New York, 134 pp. SAS Institute, 1989. User’s Guide, Version 6, 4th edn. SAS Institute, Cary, NC, USA. Stamps, J., 1995. Motor learning and the value of familiar space. Am. Nat. 146, 41–58. Thinus-Blanc, C., Bouzouba, L., Chaiz, K., Chapuis, N., Durup, M., Poucet, B., 1987. A study of spatial parameters encoded during exploration in hamsters. J. Exp. Psychol. Anim. Behav. Proc. 13, 418–427. Van Liere, D.W., 1991. Function and organisation of dustbathing in laying hens. PhD Thesis. Agricultural University, Wageningen, The Netherlands. Welker, W.I., 1957. ‘Free’ vs. ‘forced’ exploration of a novel situation by rats. Psychological Reports 3, 95–108. Wemelsfelder, F., Birke, L., 1997. Environmental challenge. In: Appleby, M.C., Hughes, B.O. ŽEds.., Animal Welfare. CAB International, Wallingford, UK, pp. 35–47. Wood-Gush, D.G.M., Vestergaard, K., 1991. The seeking of novelty and its relation to play. Anim. Behav. 42, 599–606.