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Measuring Social Behavior in Poultry1
Measuring Social Behavior in Poultry J. V. CRAIG Department of Animal Sciences and Industry, Kansas State University, Manhattan, Kansas 66506 (Received for publication August 13, 1991)
1992 Poultry Science 71:650-657
paper concentrates on chickens, because most behavioral research in poultry has Measuring social behavior is not diffi- been done with this species. Examples are cult if the animals can be seen readily, if drawn primarily from researchers who their behavior is not disturbed by the focused their attention on behavior in presence of the observer or by measuring environments similar to those encountered and recording devices, and if identifica- in poultry production. A comprehensive tion of individuals is easy. This is fre- review of the literature is not intended, quently the case with poultry after they but the examples cited should be useful in have become habituated to being observed. The author and his students have locating studies that provide considerable often gone to poultry houses equipped information on the social behavior of only with pencils, data recording sheets, poultry as well as descriptions of methodand a stop-watch or electronic timer. ology. Sometimes the use of sound recording SOCIAL BEHAVIOR devices, time-lapse video or camera, or other sophisticated equipment provides What is "social" behavior? A dictionary benefits, but lack of expensive equipment definition Webster's Ninth New Collegiate need not preclude meaningful studies. Dictionary, s.v. "social," includes "... the A good place to begin is to understand interaction of the individual and the how wild or feral relatives behave when group." Therefore, aggressive and submisrelatively free of the constraints imposed sive (agonistic) and sexually related activby humans. Such studies allow examina- ity, parental care, and behavior of the tion of the context in which different young towards the parent(s) are social, behavior patterns occur, thereby provid- because they involve direct interactions of ing insights into their functions. Tlie Red individuals with others. Social behavior Jungle Fowl, probably the ancestor of also includes activities in which individudomesticated chickens, still survives in the als show synchronized behavior, as when jungles of Southeast Asia, and wild and initiation of activity by one or a few feral flocks of other domesticated species individuals stimulates similar behavior by can be located for study. The present others. Allelomimetic feeding behavior and flighty and hysterical reactions that occur in groups are examples. Competitive activity is also social behavior and Contribution Number 92-31-J, Kansas Agriculincludes competition for mating privileges tural Experiment Station, Manhattan, KS 66506. INTRODUCTION
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ABSTRACT Social behavior of poultry is discussed in general terms, variables having major effects are indicated, and frequently used techniques of measurement are presented and compared. Studies in which different variables and methods were described are presented as examples, with primary emphasis on the behavior of chickens. (Key words: behavior, genetics, management, spacing, environment)
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BEHAVIOR IN UNCONFINED ENVIRONMENTS In natural habitats, Red Jungle Fowl are extremely wary and difficult to locate and observe. Alternative methods have involved the study of jungle fowl allowed to roam freely within the confines of a zoo (Collias et al, 1966) and observations of feral fowl in relatively undisturbed settings. For example, McBride et al. (1969) observed a population of feral fowl that had apparently survived without human assistance for more than half a century on an island of the Great Barrier Reef of
Australia. Comparisons of observations from such studies with those of domesticated fowl in human-controlled environments indicate that the behavioral repertoire seen in wild and feral relatives in unconfined environments has been largely preserved in domesticated chickens. However, the relative frequencies and intensities of expression of many behavioral traits have been altered significantly under domestication. SELECTION AND INBREEDING Selection and inbreeding of domesticated animals by humans can exert powerful influences on their social behavior. This is illustrated clearly when chickens bred for different purposes are compared in terms of agonistic behavior. Thus, chickens bred for fighting show greatly different levels of aggressive behavior as compared with meat and layer types. Interestingly, broiler and egg layer breeds, though selected for different aspects of productivity only, also differ in aggressive behavior (a genetically correlated response), as shown recently by Mench (1988). Another example of behavioral changes resulting from selection include the near elimination of broody behavior by commercial poultry breeders. In bidirectional selection studies, large differences were generated by selecting in opposite directions for social dominance ability (Craig et al, 1965) and frequency of mating of males (Siegel, 1965). Although not studied as intensively as selection effects, inbreeding without selection has been demonstrated to reduce social dominance ability (Craig a n d Baruth, 1965). Also, random genetic drift in small populations selected for egg production is the most likely explanation for large differences found between lines for a measure of fearfulness (Craig et al, 1983). MANAGEMENT INFLUENCES In a classic study, Guhl and Allee (1944) found that organized flocks of hens had much lower frequencies of agonistic acts than flocks in which strange hens were frequently added and removed. Siegel and Siegel (1961), following up on that study,
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and for space at the feeder or other favored locations. Should feather pecking and cannibalism be included as social behavior? Evidence supports the contention that these activities involve redirected feeding or groundpecking behavior (Wennrich, 1974; Blokhuis and Arkes, 1984; Blokhuis, 1986). Nevertheless, both feather and cannibalistic pecking contain elements of social behavior, because the activity of the perpetrators impinges on the well-being of the recipients. However, feather and cannibalistic pecking are not aggressive acts. Aggressive acts are directed primarily to the head and neck regions of subordinate birds, whereas lower-status hens may take part in cannibalistic pecking of more dominant individuals, and the pecks are directed to areas away from the head. In examining social interactions between individuals, it often is useful to break down a major category of behavior into its component parts. For example, in mating behavior, courting precedes copulation and there is a complex sequence of signals and responses between male and female that must occur before a successful mating results. This was illustrated schematically for chickens by Guhl (1962) and for turkeys by Hale and Schein (1962). The situation becomes more complex when more than a single pair is involved, and it may then be instructive to examine interactions within each sex as well as those between sexes. Thus, Kratzer and Craig (1980) determined that males of higher social rank mounted more, mated more, and interfered more with matings of lower ranking males.
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was shown to be important by MeunierSalaun and Faure (1984-1985). They found that subordinate hens frequently came close to more dominant hens to feed, although they risked being pecked by doing so and additional feeding space was available further away.
GENETIC-ENVIRONMENT INTERACTIONS Occasionally, results obtained in different studies appear to be contradictory. At least some of those discrepancies may be accounted for by behavioral differences among genetic stocks that respond differently to the same management systems or environmental conditions. As the knowledge of management systems increases, it becomes desirable that more than one stock should be included in studies, so that conclusions may be generalized with greater validity. For example, a recent series of experiments (Kuo et ah, 1991; Lee and Craig, 1991; Craig and Lee, 1989, 1990) indicated that benefits derived from beak trimming vary significantly among stocks. One comparison involving three commercial stocks (Craig and Lee, 1989) showed that hens of all stocks had low levels of mortality from cannibalism when beaks were trimmed, although hens of two of the stocks had high incidences of mortality from this cause when their beaks were intact. In contrast, those of the third stock had no higher incidence of beakinflicted mortality when beaks were intact.
ADAPTATION TO CHANGES AND OBSERVERS Adaptation of poultry to novel experiences and environments and to stimuli provided by handling or by the presence of human beings is worthy of study. However, when those effects are not the subject of interest, care must be taken to eliminate or reduce their importance, so as to avoid confounding them with experimental treatments. Handbooks dealing with observational techniques by Lehner (1979) and Martin and Bateson (1986) provide excellent guidelines on how to avoid or minimize such problems, as well as general information on observational techniques.
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found that the social stress associated with the repeated introduction of strangers into organized flocks can be useful in providing stressed individuals for physiological experiments. Frustration is a powerful stimulus for initiating aggression, as found by Duncan and Wood-Gush (1971). They demonstrated that dominant birds, when hungry and frustrated in a feeding situation, became highly abusive of subordinates that they would otherwise tolerate when not hungry. Studies by Polley et ah (1974) of frequencies of agonistic acts in groups kept under different levels of crowding suggested that a curvilinear response was present. Al-Rawi and Craig (1975), noting that "crowding", as frequently described, confounded the effects of area per individual (density) and group size, studied the effects of each of those variables independently. They learned that when hens were feeding or moving about, there were higher levels of agonistic acts in larger groups, at least during the first 2 mo after strangers were placed together. When flocks with different areas per bird were compared while holding group size constant, Al-Rawi and Craig (1975) observed that frequencies of agonistic acts were greatest at intermediate densities. A further investigation by Ylander and Craig (1980) indicated that a "dominant third party" effect was associated with the reduced frequency of agonistic acts observed at higher densities. Beak trimming is a management practice that alters the beak so that its effectiveness as a reinforcer of dominance is reduced, apparently resulting in more frequent but less painful pecks (Hale, 1948). Beak trimming also makes the beak less effective for pulling feathers and inflicting damage by cannibalistic pecking (Craig and Lee, 1990). Frequently overlooked is the fact that chickens benefit from living in social groups, at least under natural conditions (McBride et ah, 1969). This phenomenon goes largely unnoticed in the high-density environments commonly found under commercial conditions, where the tendency for birds to come together is obscured by lack of space. The attractiveness of other birds, at least during feeding,
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SPACING RELATIONSHIPS
AGONISTIC BEHAVIOR AND PECKING ORDERS Most studies of agonistic behavior and pecking orders are carried out late in the rearing period or after sexual maturity. Although agonistic pecking begins to occur within a few weeks after hatching, stable dominance-subordinance relationships usually do not become established until 6 to 8 wk of age in cockerels and 8 to 10 wk in pullets, as shown by Guhl (1958). In the same study, Guhl (1958) also found that juvenile clucks work out their dominance relationships at a slower rate if kept in intact rearing groups than if mixed with strangers. Hormonal effects associated with sexual maturity appear to be of major importance in causing the onset of aggressive behavior. Evidence from experimental stocks selected bidirectionally for high and low social dominance (Craig et ah, 1965) suggests that the level of sensitivity to androgenic stimulation may be as important, or perhaps even more important, than endogenous levels of circulating androgens (Ortman and Craig, 1968) in influencing aggressive behavior and social dominance. Within groups, pullets that become sexually mature early have a developmentally related advantage in establishing dominance over later maturing pullets (Craig et ah, 1975; Bhagwat and Craig, 1977). Once established, pecking orders exhibit "social inertia", and dominance relationships tend to persist, especially among females, even when potential ability to win contests with strangers changes significantly (Tindell and Craig, 1959; Lee and Craig, 1981). In addition to the effects of social inertia, it has been known since the 1940s that other psychological influences have an important bearing on status attained in initial encounters between strange birds. For example, Collias (1943) showed that individuals had greater success in winning initial pair contests when they were in familiar s u r r o u n d i n g s and a m o n g acquaintances. Also, McBride (1958) found that winners and losers of pair contests were more likely to win and lose in subsequent initial pair contests, respectively, if the second contest occurred after only a short lapse of time (less than 3 h) rather than a longer interval.
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Animals both attract and repel each other, depending on a complex variety of circumstances (McBride, 1971). In natural environments, territorial and home-range behaviors come into play as well as within-group interactions (McBride et ah, 1969). "Site attachments" usually occur when group size is relatively large in environments provided by humans. This has been shown for mated cockerels (Pamment et ah, 1982-1983) and for mature hens in unisexual flocks (McBride and Foenander, 1962; Craig and Guhl, 1969). "Pecking pressure" appears to operate as a reinforcer, which tends to keep each bird within its area of attachment. Craig and Guhl (1969) learned that hens were more dominant in areas where they spent more time than when they moved into less frequented areas. However, results obtained by Hughes et ah (1974), with hens of a stock showing little aggressiveness and kept in a house with very dim lights, indicated that only some birds showed site attachments u n d e r those conditions, whereas others appeared to move about randomly. Pamment et ah (1982-1983:342), in referring to their results with cockerels, hypothesized that " . . . site attachment with spatial defence can occur only when space is adequate; this behaviour is essentially territorial, since birds are dominant over the area and have priority in mating." In artificial environments containing fewer birds and that are too small for "territories", pecking order status is of primary importance; higher ranking males are involved in more matings (Guhl and Warren, 1946; Kratzer and Craig, 1980; Pamment et ah, 1982-1983) and subordinate males sometimes hide in corners or retreat to roosts or nests (Craig and Bhagwat, 1974). Although agonistic behavior tends to increase spacing between birds because of maintenance of each animal's personal space, social bonds (mother-young bonds, imprinting-related bonds, and sexual bonds in some species) and social releasers cause animals to seek closer spatial associations with each other (Craig, 1981).
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CKeefe et al (1988) suggest that linear pecking orders are not common when four or six hens are kept together in cages of commercial design and are difficult to determine because of the low incidence of agonistic acts observed under conditions of relatively high density. CKeefe et al (1988) reported that despotic organization was more likely to be observed than linear pecking orders. A study by Lee et al (1982) indicated the complexities of social organization likely to be found in floor pens, even with relatively small flocks of 24 hens. The greater difficulty of obtaining data on agonistic behavior in high-density environments is clear from the studies of AlRawi and Craig (1975) and CKeefe et al (1988), who found that the frequency of aggressive acts is greatly inhibited in highdensity as compared with moderately spacious accommodations. This problem makes it very difficult to determine pecking orders in high-density cages. The situation becomes more manageable when time-lapse video recording of behavior is used, especially at times when agonistic activity is likely to be at higher levels, for example, soon after strange hens are placed together in cages (Craig et al, 1988) and after moderate feed deprivation followed by provision of feed but with restriction of access (Craig and Ramos, 1986). Those studies also indicated that most agonistic acts occurred adjacent to the feeder.
SOCIAL STATUS IN LARGER GROUPS The number of unidirectional dominance pair relationships among n birds is (n 2 - n) + 2. Therefore, even flocks of relatively small size potentially contain so many relationships that very large investments of observation time are required to determine social interactions between all pairs of birds. An illustration is provided by a study of Guhl (1953), w h o attempted to determine the peck order in a flock of 96 hens. Many hours of observation yielded information on 17,851 aggressive pecks. Nevertheless, many pair relationships remained unknown. Perhaps some pairs did not interact, either because of mutual tolerance or because they re-
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The potential ability of a bird to attain dominance has often been estimated from the outcome of initial pair contests in which strangers of the same age and sex were placed together in a neutral area. This method may speed up the process of evaluating social-dominance potential and avoid some of the psychological problems mentioned. Nevertheless, staged contests involve highly artificial conditions, and outcomes could be influenced by other extraneous variables, such as differences in relative fearfulness resulting from being handled by the human evaluator or from the test environment. Estimated dominance potentials are relative to other individuals used in the test. Selected "panels" of opponents have been used (McBride, 1958), as well as random samples of individuals of the same or of different genetic stocks (Craig et al, 1965). When Guhl (1953) compared relative status of adult hens evaluated by the initialpair contest method and by social rank in organized groups involving the same individuals, only moderate correlation coefficients were obtained, ranging from about .3 to .8. In spite of some of the questions associated with the use of the initial pair contest method of evaluating social dominance potential, this method of testing has been successful for differentiating genetic stocks in bidirectional selection studies (Guhl et al, 1960; Craig et al, 1965). In each study, after a few generations of selection, stocks were produced that differed markedly in dominance ability. Differences among the stocks were also present when they were tested by assembling pullets of the selected stocks that were strangers to each other in flocks (Craig et al, 1965). Social organization within groups can be relatively simple (i.e., linear or near linear) or highly complex (SchjelderupEbbe, 1922; Guhl, 1953). Appleby (1983) examined the probability of linearities in social hierarchies and found that, although several investigators have emphasized the apparent prevalence of linear hierarchies in flocks of a few hens, linearity often can be an artifact resulting from chance, faulty assumptions, and insufficient data. Results obtained by Craig and Ramos (1986) and
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as to location and agonistic interactions with other individuals indicated that time spent in particular locations and dominance ratios were positively correlated in larger flocks. Another measure called the "social tension index" was devised by Craig et al. (1969) for use in pens where all individuals were identified. For this estimate, the number of submissive acts is subtracted from the number of aggressive acts. Social tension indexes yielded frequency distributions for individuals within flocks that approached normality and were shown to be correlated at relatively low, but usually significant, levels with production traits (Biswas and Craig, 1971). Lee et al. (1982) provided a measure called the "social rank index" that was based on known pair relationships. For any of the three measures, i.e., dominance ratios, social tension indexes, or social rank indexes, it is not required that all pair relationships be known. This is an obvious advantage when working with large flocks. Which method of ranking social status is preferable? Lee et al. (1982) used both social tension indexes and social rank indexes on the same groups of hens being kept in pens of 24 each. They found that the two measures were highly correlated, but social rank indexes more closely approached normal distributions. These indexes then were compared with productivity data to determine whether the associations between those measures supported McBride's hypothesis (McBride, 1964) that only the lowest ranking birds within flocks were much depressed in performance.
ACCESS TO SCARCE RESOURCES Estimates of relative status usually involve recording either aggressive and submissive acts or relative access to scarce resources. Use of agonistic acts is much preferred, unless the measure of access has been validated as an accurate indicator of status. Thus, Banks et al. (1979) determined pecking orders within small groups of birds in pens with feed and water continuously available. Subsequently, birds were deprived of feed and water and then placed together for brief periods
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mained in different parts of the pen. Alternatively, further observations might have filled the existing gaps. Whatever the situation, it becomes evident that sampling procedures may be required when working with larger groups or with a number of smaller groups. Randomly identifying individuals as samples of larger populations is useful in behavioral studies. Most investigators avoid changing the appearance of the head and neck of birds, because Guhl and Ortman (1953) found that hens whose appearance was altered in those areas were attacked as if they were strangers by penmates. Alterations of other parts of the body often attracted attention initially, but marked hens retained their status within the group. As indicated previously, pecking orders can be complex and involve many "pecking triangles" in which nontransitive dominance relationships exist. For example, in considering Individuals A, B, and C, it is often found that A is dominant to B and B is dominant to C, but C is dominant to A. Thus, within the pecking triangle, each bird is dominant to one and submissive to another of the triad. When several or many pecking triangles exist, it becomes difficult to assign social status ranks to the individuals involved. Although in each pair relationship one bird is dominant and the other subordinate, the quality of the relationship may vary greatly; in some pairs, the dominant individual may be extremely abusive, whereas in others, considerable tolerance towards the subordinate exists. The most common measure of status in the past has been based on the number of others in the group known to be dominated. However, to get a measure that indicates the relative frequencies of aggressive acts delivered by an individual, "dominance ratios", based on number of aggressive acts divided by total agonistic acts, were used by Craig and Guhl (1969). Dominance ratios can measure the relative status in large flocks in which only a moderate number of birds are selected randomly to be marked and observed as "focal animals." This was found to be a useful measure. Observing the sample of marked individuals one bird at a time for predetermined time periods
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REFERENCES Al-Rawi, B., and J. V. Craig, 1975. Agonistic behavior of caged chickens related to group size and area per bird. Appl. Anim. Ethol. 2:69-80. Appleby, M. C , 1983. The probability of linearity in hierarchies. Anim. Behav. 31:600-608.
Banks, E. M, D.G.M. Wood-Gush, B. O. Hughes, and N. J. Mankovich, 1979. Social rank and priority of access to resources in domestic fowl. Behav. Processes 4:197-209. Bhagwat, A. L., and J. V. Craig, 1977. Selecting for age at first egg: effects on social dominance. Poultry Sci. 56:361-363. Biswas, D. K., and J. V. Craig, 1971. Social tension indexes and egg production traits in chickens. Poultry Sci. 50:1063-1065. Blokhuis, H. J., 1986. Feather pecking in poultry: its relation with ground pecking. Appl. Anim. Behav. Sci. 16:63-67. Blokhuis, H. J., and J. G. Arkes, 1984. Some observations on the development of featherpecking in poultry. Appl. Arum. Behav. Sci. 12: 145-157. Collias, N. E., 1943. Statistical analysis of factors which make for success in initial encounters between hens. Am. Nat. 77:529-538. Collias, N. E., E. C. Collias, D. Hunsaker, and L. Minning, 1966. Locality fixation, mobility and social organization within an unconfined population of Red Jungle Fowl. Anim. Behav. 14: 550-559. Craig, J. V., 1981. Social behavior effects on spacing. Pages 32-53 in: Domestic Animal Behavior. Prentice-Hall, Inc., Englewood Cliffs, NJ. Craig, J. V., and R. A. Baruth, 1965. Inbreeding and social dominance ability in chickens. Anim. Behav. 13:109-113. Craig, J. V., and A. L. Bhagwat, 1974. Agonistic and mating behavior of adult chickens modified by social and physical environments. Appl. Anim. Ethol. 1:57-65. Craig, J. V., D. K. Biswas, and A. M. Guhl, 1969. Agonistic behaviour influenced by strangeness, crowding and heredity in female domestic fowL Anim. Behav. 17:498-506. Craig, J. V., T. P. Craig, and A. D. Dayton, 1983. Fearful behavior by caged hens of two genetic stocks. Appl. Anim. Ethol. 10:263-273. Craig, J. V., and A. M. Guhl, 1969. Territorial behavior and social interactions of pullets kept in large flocks. Poultry Sci. 48:1622-1628. Craig, J. V., M.-L. Jan, C. R. Polley, A. L. Bhagwat, and A. D. Dayton, 1975. Changes in relative aggressiveness and social dominance associated with selection for early egg production in chickens. Poultry Sci. 54:1647-1658. Craig, J. V., and H.-Y. Lee, 1989. Research note: Genetic stocks of White Leghorn type differ in relative productivity when beaks are intact versus trimmed. Poultry Sci. 68:1720-1723. Craig, J. V., and H.-Y. Lee, 1990. Beak trimming and genetic stock effects on behavior and mortality from cannibalism in White Leghorn-type pullets. Appl. Anim. Behav. Sci. 25:107-123. Craig, J. V., N. A. Okpokho, and G. A. Milliken, 1988. Floor- and cage-rearing effects on pullets' initial adaptation to multiple-hen cages. Appl. Anim. Behav. Sci. 20:319-333. Craig, J. V., L. L. Qrtman, and A. M. Guhl, 1965. Genetic selection for social dominance ability in chickens. Anim. Behav. 13:114-131. Craig, J. V., and N. C. Ramos, 1986. Competitive feeding behavior and social status in multiplehen cages. Appl. Anim. Behav. Sci. 16:69-76. Duncan, I.J.H., and D.G.M. Wood-Gush, 1971. Frus-
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in a pen with feed and water available at point sources, i.e., so that only one bird could gain access at a time. There was a significant, but not perfect, relationship between social rank and frequency and duration of feeding. However, thirsty birds did not compete at the water source. Whichever bird arrived first was allowed to drink its fill, regardless of its dominance rank. In a cage environment, when the feeder was attached outside the cage, an association between rank and access to restricted feeder space was not found (Craig and Ramos, 1986). Displacements at the opening to the feeder were frequent, and hens often achieved access by crawling under or over the bird that had been feeding. In this situation, subordinate birds were not required to face dominants that were displaced. Clearly, the level of motivation and amount of effort required to gain access to a scarce resource, as well as social status, is relevant to whether an individual gains access. A study by King (1965) indicated that frustrating situations may become so extreme with cockerels that dominant individuals do not necessarily control access. Syme (1974) has been particularly critical of using measures of ability to gain access to resources as a criterion of relative social status. Most poultry scientists interested in applied research want to know how dominance and competitive ranks are associated with each other and with wellbeing and production characteristics. The various measures discussed need to be tested for such associations. When associations are found between estimators of status and other traits, evidence is provided that needed resources may not be obtainable at desirable levels by lowerranking birds. Genetic effects, management systems, and physical and social environments are then opened to scrutiny to determine whether behavioral or other problems are causing inequities to arise.
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tration and aggression in the domestic fowl. Arum. Behav. 19:500-504. Guhl, A. M., 1953. Social behavior of the domestic fowl. Kansas Agricultural Experiment Station Technical Bulletin 73:1-48. Guhl, A. M., 1958. The development of social organisation in the domestic chick. Anim. Behav. 652-111. Guhl, A. M., 1962. The behaviour of chickens. Pages 491-530 in: The Behaviour of Domestic Animals. E.S.E. Hafez, ed. The Williams and Wilkins Company, Baltimore, MD. Guhl, A. M., and W. C. AUee, 1944. Some measurable effects of social organization in flocks of hens. Physiol. Zool. 17:320-347. Guhl, A. M., J. V. Craig, and C. D. Mueller, 1960. Selective breeding for aggressiveness in chickens. Poultry Sci. 39:970-980. Guhl, A. M., and L. L. Ortman, 1953. Visual patterns in the recognition of individuals among chickens. Condor 55387-298. Guhl, A. M., and D. C. Warren, 1946. Number of offspring sired by cockerels related to social dominance in chickens. Poultry Sci. 25:460-472. Hale, E. B., 1948. Observations on the social behavior of hens following debeaking. Poultry Sci. 27: 591-592. Hale, E. B., and M. W. Schein, 1962. The behaviour of turkeys. Pages 531-564 in: The Behaviour of Domestic Animals. E.S.E. Hafez, ed. The Williams and Wilkins Company, Baltimore, MD. Hughes, B. O., D.G.M. Wood-Gush, and R. M. Jones, 1974. Spatial organization in flocks of domestic fowls. Arum. Behav. 22:438-445. King, M. G., 1965. Disruptions of the pecking order of cockerels concomitant with degrees of accessibility to feed. Anim. Behav. 13:504-506. Kratzer, D. D., and J. V. Craig, 1980. Mating behavior of cockerels: effects of social status, group size, and group density. Appl. Anim. Ethol. 6:49-62. Kuo, F.-L., J. V. Craig, and W. M. Muir, 1991. Selection and beak-trimming effects on behavior, cannibalism, and short-term production traits in White Leghorn pullets. Poultry Sci. 70: 1057-1068. Lee, H.-Y., and J. V. Craig, 1991. Beak trimming effects on behavior patterns, fearfulness, feathering, and mortality among three stocks of White Leghorn pullets in cages or floor pens. Poultry Sci. 70:211-221. Lee, Y.-P., and J. V. Craig, 1981. Agonistic and nonagonistic behaviors of pullets of dissimilar strains of White Leghorns when kept separately and intermingled. Poultry Sci. 60:1759-1768. Lee, Y.-P., J. V. Craig, and A. D. Dayton, 1982. The social rank index as a measure of social status and its association with egg production in White Leghorn pullets. Appl. Anim. Ethol. 8: 377-390. Lehner, P. N., 1979. Handbook of Ethological Methods. Garland STPM Press, New York, NY. Martin, P., and P. Bateson, 1986. Measuring Behavior.
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paper concentrates on chickens, because most behavioral research in poultry has Measuring social behavior is not diffi- been done with this species. Examples are cult if the animals can be seen readily, if drawn primarily from researchers who their behavior is not disturbed by the focused their attention on behavior in presence of the observer or by measuring environments similar to those encountered and recording devices, and if identifica- in poultry production. A comprehensive tion of individuals is easy. This is fre- review of the literature is not intended, quently the case with poultry after they but the examples cited should be useful in have become habituated to being observed. The author and his students have locating studies that provide considerable often gone to poultry houses equipped information on the social behavior of only with pencils, data recording sheets, poultry as well as descriptions of methodand a stop-watch or electronic timer. ology. Sometimes the use of sound recording SOCIAL BEHAVIOR devices, time-lapse video or camera, or other sophisticated equipment provides What is "social" behavior? A dictionary benefits, but lack of expensive equipment definition Webster's Ninth New Collegiate need not preclude meaningful studies. Dictionary, s.v. "social," includes "... the A good place to begin is to understand interaction of the individual and the how wild or feral relatives behave when group." Therefore, aggressive and submisrelatively free of the constraints imposed sive (agonistic) and sexually related activby humans. Such studies allow examina- ity, parental care, and behavior of the tion of the context in which different young towards the parent(s) are social, behavior patterns occur, thereby provid- because they involve direct interactions of ing insights into their functions. Tlie Red individuals with others. Social behavior Jungle Fowl, probably the ancestor of also includes activities in which individudomesticated chickens, still survives in the als show synchronized behavior, as when jungles of Southeast Asia, and wild and initiation of activity by one or a few feral flocks of other domesticated species individuals stimulates similar behavior by can be located for study. The present others. Allelomimetic feeding behavior and flighty and hysterical reactions that occur in groups are examples. Competitive activity is also social behavior and Contribution Number 92-31-J, Kansas Agriculincludes competition for mating privileges tural Experiment Station, Manhattan, KS 66506. INTRODUCTION
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ABSTRACT Social behavior of poultry is discussed in general terms, variables having major effects are indicated, and frequently used techniques of measurement are presented and compared. Studies in which different variables and methods were described are presented as examples, with primary emphasis on the behavior of chickens. (Key words: behavior, genetics, management, spacing, environment)
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BEHAVIOR IN UNCONFINED ENVIRONMENTS In natural habitats, Red Jungle Fowl are extremely wary and difficult to locate and observe. Alternative methods have involved the study of jungle fowl allowed to roam freely within the confines of a zoo (Collias et al, 1966) and observations of feral fowl in relatively undisturbed settings. For example, McBride et al. (1969) observed a population of feral fowl that had apparently survived without human assistance for more than half a century on an island of the Great Barrier Reef of
Australia. Comparisons of observations from such studies with those of domesticated fowl in human-controlled environments indicate that the behavioral repertoire seen in wild and feral relatives in unconfined environments has been largely preserved in domesticated chickens. However, the relative frequencies and intensities of expression of many behavioral traits have been altered significantly under domestication. SELECTION AND INBREEDING Selection and inbreeding of domesticated animals by humans can exert powerful influences on their social behavior. This is illustrated clearly when chickens bred for different purposes are compared in terms of agonistic behavior. Thus, chickens bred for fighting show greatly different levels of aggressive behavior as compared with meat and layer types. Interestingly, broiler and egg layer breeds, though selected for different aspects of productivity only, also differ in aggressive behavior (a genetically correlated response), as shown recently by Mench (1988). Another example of behavioral changes resulting from selection include the near elimination of broody behavior by commercial poultry breeders. In bidirectional selection studies, large differences were generated by selecting in opposite directions for social dominance ability (Craig et al, 1965) and frequency of mating of males (Siegel, 1965). Although not studied as intensively as selection effects, inbreeding without selection has been demonstrated to reduce social dominance ability (Craig a n d Baruth, 1965). Also, random genetic drift in small populations selected for egg production is the most likely explanation for large differences found between lines for a measure of fearfulness (Craig et al, 1983). MANAGEMENT INFLUENCES In a classic study, Guhl and Allee (1944) found that organized flocks of hens had much lower frequencies of agonistic acts than flocks in which strange hens were frequently added and removed. Siegel and Siegel (1961), following up on that study,
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and for space at the feeder or other favored locations. Should feather pecking and cannibalism be included as social behavior? Evidence supports the contention that these activities involve redirected feeding or groundpecking behavior (Wennrich, 1974; Blokhuis and Arkes, 1984; Blokhuis, 1986). Nevertheless, both feather and cannibalistic pecking contain elements of social behavior, because the activity of the perpetrators impinges on the well-being of the recipients. However, feather and cannibalistic pecking are not aggressive acts. Aggressive acts are directed primarily to the head and neck regions of subordinate birds, whereas lower-status hens may take part in cannibalistic pecking of more dominant individuals, and the pecks are directed to areas away from the head. In examining social interactions between individuals, it often is useful to break down a major category of behavior into its component parts. For example, in mating behavior, courting precedes copulation and there is a complex sequence of signals and responses between male and female that must occur before a successful mating results. This was illustrated schematically for chickens by Guhl (1962) and for turkeys by Hale and Schein (1962). The situation becomes more complex when more than a single pair is involved, and it may then be instructive to examine interactions within each sex as well as those between sexes. Thus, Kratzer and Craig (1980) determined that males of higher social rank mounted more, mated more, and interfered more with matings of lower ranking males.
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was shown to be important by MeunierSalaun and Faure (1984-1985). They found that subordinate hens frequently came close to more dominant hens to feed, although they risked being pecked by doing so and additional feeding space was available further away.
GENETIC-ENVIRONMENT INTERACTIONS Occasionally, results obtained in different studies appear to be contradictory. At least some of those discrepancies may be accounted for by behavioral differences among genetic stocks that respond differently to the same management systems or environmental conditions. As the knowledge of management systems increases, it becomes desirable that more than one stock should be included in studies, so that conclusions may be generalized with greater validity. For example, a recent series of experiments (Kuo et ah, 1991; Lee and Craig, 1991; Craig and Lee, 1989, 1990) indicated that benefits derived from beak trimming vary significantly among stocks. One comparison involving three commercial stocks (Craig and Lee, 1989) showed that hens of all stocks had low levels of mortality from cannibalism when beaks were trimmed, although hens of two of the stocks had high incidences of mortality from this cause when their beaks were intact. In contrast, those of the third stock had no higher incidence of beakinflicted mortality when beaks were intact.
ADAPTATION TO CHANGES AND OBSERVERS Adaptation of poultry to novel experiences and environments and to stimuli provided by handling or by the presence of human beings is worthy of study. However, when those effects are not the subject of interest, care must be taken to eliminate or reduce their importance, so as to avoid confounding them with experimental treatments. Handbooks dealing with observational techniques by Lehner (1979) and Martin and Bateson (1986) provide excellent guidelines on how to avoid or minimize such problems, as well as general information on observational techniques.
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found that the social stress associated with the repeated introduction of strangers into organized flocks can be useful in providing stressed individuals for physiological experiments. Frustration is a powerful stimulus for initiating aggression, as found by Duncan and Wood-Gush (1971). They demonstrated that dominant birds, when hungry and frustrated in a feeding situation, became highly abusive of subordinates that they would otherwise tolerate when not hungry. Studies by Polley et ah (1974) of frequencies of agonistic acts in groups kept under different levels of crowding suggested that a curvilinear response was present. Al-Rawi and Craig (1975), noting that "crowding", as frequently described, confounded the effects of area per individual (density) and group size, studied the effects of each of those variables independently. They learned that when hens were feeding or moving about, there were higher levels of agonistic acts in larger groups, at least during the first 2 mo after strangers were placed together. When flocks with different areas per bird were compared while holding group size constant, Al-Rawi and Craig (1975) observed that frequencies of agonistic acts were greatest at intermediate densities. A further investigation by Ylander and Craig (1980) indicated that a "dominant third party" effect was associated with the reduced frequency of agonistic acts observed at higher densities. Beak trimming is a management practice that alters the beak so that its effectiveness as a reinforcer of dominance is reduced, apparently resulting in more frequent but less painful pecks (Hale, 1948). Beak trimming also makes the beak less effective for pulling feathers and inflicting damage by cannibalistic pecking (Craig and Lee, 1990). Frequently overlooked is the fact that chickens benefit from living in social groups, at least under natural conditions (McBride et ah, 1969). This phenomenon goes largely unnoticed in the high-density environments commonly found under commercial conditions, where the tendency for birds to come together is obscured by lack of space. The attractiveness of other birds, at least during feeding,
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SPACING RELATIONSHIPS
AGONISTIC BEHAVIOR AND PECKING ORDERS Most studies of agonistic behavior and pecking orders are carried out late in the rearing period or after sexual maturity. Although agonistic pecking begins to occur within a few weeks after hatching, stable dominance-subordinance relationships usually do not become established until 6 to 8 wk of age in cockerels and 8 to 10 wk in pullets, as shown by Guhl (1958). In the same study, Guhl (1958) also found that juvenile clucks work out their dominance relationships at a slower rate if kept in intact rearing groups than if mixed with strangers. Hormonal effects associated with sexual maturity appear to be of major importance in causing the onset of aggressive behavior. Evidence from experimental stocks selected bidirectionally for high and low social dominance (Craig et ah, 1965) suggests that the level of sensitivity to androgenic stimulation may be as important, or perhaps even more important, than endogenous levels of circulating androgens (Ortman and Craig, 1968) in influencing aggressive behavior and social dominance. Within groups, pullets that become sexually mature early have a developmentally related advantage in establishing dominance over later maturing pullets (Craig et ah, 1975; Bhagwat and Craig, 1977). Once established, pecking orders exhibit "social inertia", and dominance relationships tend to persist, especially among females, even when potential ability to win contests with strangers changes significantly (Tindell and Craig, 1959; Lee and Craig, 1981). In addition to the effects of social inertia, it has been known since the 1940s that other psychological influences have an important bearing on status attained in initial encounters between strange birds. For example, Collias (1943) showed that individuals had greater success in winning initial pair contests when they were in familiar s u r r o u n d i n g s and a m o n g acquaintances. Also, McBride (1958) found that winners and losers of pair contests were more likely to win and lose in subsequent initial pair contests, respectively, if the second contest occurred after only a short lapse of time (less than 3 h) rather than a longer interval.
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Animals both attract and repel each other, depending on a complex variety of circumstances (McBride, 1971). In natural environments, territorial and home-range behaviors come into play as well as within-group interactions (McBride et ah, 1969). "Site attachments" usually occur when group size is relatively large in environments provided by humans. This has been shown for mated cockerels (Pamment et ah, 1982-1983) and for mature hens in unisexual flocks (McBride and Foenander, 1962; Craig and Guhl, 1969). "Pecking pressure" appears to operate as a reinforcer, which tends to keep each bird within its area of attachment. Craig and Guhl (1969) learned that hens were more dominant in areas where they spent more time than when they moved into less frequented areas. However, results obtained by Hughes et ah (1974), with hens of a stock showing little aggressiveness and kept in a house with very dim lights, indicated that only some birds showed site attachments u n d e r those conditions, whereas others appeared to move about randomly. Pamment et ah (1982-1983:342), in referring to their results with cockerels, hypothesized that " . . . site attachment with spatial defence can occur only when space is adequate; this behaviour is essentially territorial, since birds are dominant over the area and have priority in mating." In artificial environments containing fewer birds and that are too small for "territories", pecking order status is of primary importance; higher ranking males are involved in more matings (Guhl and Warren, 1946; Kratzer and Craig, 1980; Pamment et ah, 1982-1983) and subordinate males sometimes hide in corners or retreat to roosts or nests (Craig and Bhagwat, 1974). Although agonistic behavior tends to increase spacing between birds because of maintenance of each animal's personal space, social bonds (mother-young bonds, imprinting-related bonds, and sexual bonds in some species) and social releasers cause animals to seek closer spatial associations with each other (Craig, 1981).
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CKeefe et al (1988) suggest that linear pecking orders are not common when four or six hens are kept together in cages of commercial design and are difficult to determine because of the low incidence of agonistic acts observed under conditions of relatively high density. CKeefe et al (1988) reported that despotic organization was more likely to be observed than linear pecking orders. A study by Lee et al (1982) indicated the complexities of social organization likely to be found in floor pens, even with relatively small flocks of 24 hens. The greater difficulty of obtaining data on agonistic behavior in high-density environments is clear from the studies of AlRawi and Craig (1975) and CKeefe et al (1988), who found that the frequency of aggressive acts is greatly inhibited in highdensity as compared with moderately spacious accommodations. This problem makes it very difficult to determine pecking orders in high-density cages. The situation becomes more manageable when time-lapse video recording of behavior is used, especially at times when agonistic activity is likely to be at higher levels, for example, soon after strange hens are placed together in cages (Craig et al, 1988) and after moderate feed deprivation followed by provision of feed but with restriction of access (Craig and Ramos, 1986). Those studies also indicated that most agonistic acts occurred adjacent to the feeder.
SOCIAL STATUS IN LARGER GROUPS The number of unidirectional dominance pair relationships among n birds is (n 2 - n) + 2. Therefore, even flocks of relatively small size potentially contain so many relationships that very large investments of observation time are required to determine social interactions between all pairs of birds. An illustration is provided by a study of Guhl (1953), w h o attempted to determine the peck order in a flock of 96 hens. Many hours of observation yielded information on 17,851 aggressive pecks. Nevertheless, many pair relationships remained unknown. Perhaps some pairs did not interact, either because of mutual tolerance or because they re-
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The potential ability of a bird to attain dominance has often been estimated from the outcome of initial pair contests in which strangers of the same age and sex were placed together in a neutral area. This method may speed up the process of evaluating social-dominance potential and avoid some of the psychological problems mentioned. Nevertheless, staged contests involve highly artificial conditions, and outcomes could be influenced by other extraneous variables, such as differences in relative fearfulness resulting from being handled by the human evaluator or from the test environment. Estimated dominance potentials are relative to other individuals used in the test. Selected "panels" of opponents have been used (McBride, 1958), as well as random samples of individuals of the same or of different genetic stocks (Craig et al, 1965). When Guhl (1953) compared relative status of adult hens evaluated by the initialpair contest method and by social rank in organized groups involving the same individuals, only moderate correlation coefficients were obtained, ranging from about .3 to .8. In spite of some of the questions associated with the use of the initial pair contest method of evaluating social dominance potential, this method of testing has been successful for differentiating genetic stocks in bidirectional selection studies (Guhl et al, 1960; Craig et al, 1965). In each study, after a few generations of selection, stocks were produced that differed markedly in dominance ability. Differences among the stocks were also present when they were tested by assembling pullets of the selected stocks that were strangers to each other in flocks (Craig et al, 1965). Social organization within groups can be relatively simple (i.e., linear or near linear) or highly complex (SchjelderupEbbe, 1922; Guhl, 1953). Appleby (1983) examined the probability of linearities in social hierarchies and found that, although several investigators have emphasized the apparent prevalence of linear hierarchies in flocks of a few hens, linearity often can be an artifact resulting from chance, faulty assumptions, and insufficient data. Results obtained by Craig and Ramos (1986) and
SYMPOSIUM: QUANTIFYING THE BEHAVIOR OF POULTRY
as to location and agonistic interactions with other individuals indicated that time spent in particular locations and dominance ratios were positively correlated in larger flocks. Another measure called the "social tension index" was devised by Craig et al. (1969) for use in pens where all individuals were identified. For this estimate, the number of submissive acts is subtracted from the number of aggressive acts. Social tension indexes yielded frequency distributions for individuals within flocks that approached normality and were shown to be correlated at relatively low, but usually significant, levels with production traits (Biswas and Craig, 1971). Lee et al. (1982) provided a measure called the "social rank index" that was based on known pair relationships. For any of the three measures, i.e., dominance ratios, social tension indexes, or social rank indexes, it is not required that all pair relationships be known. This is an obvious advantage when working with large flocks. Which method of ranking social status is preferable? Lee et al. (1982) used both social tension indexes and social rank indexes on the same groups of hens being kept in pens of 24 each. They found that the two measures were highly correlated, but social rank indexes more closely approached normal distributions. These indexes then were compared with productivity data to determine whether the associations between those measures supported McBride's hypothesis (McBride, 1964) that only the lowest ranking birds within flocks were much depressed in performance.
ACCESS TO SCARCE RESOURCES Estimates of relative status usually involve recording either aggressive and submissive acts or relative access to scarce resources. Use of agonistic acts is much preferred, unless the measure of access has been validated as an accurate indicator of status. Thus, Banks et al. (1979) determined pecking orders within small groups of birds in pens with feed and water continuously available. Subsequently, birds were deprived of feed and water and then placed together for brief periods
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mained in different parts of the pen. Alternatively, further observations might have filled the existing gaps. Whatever the situation, it becomes evident that sampling procedures may be required when working with larger groups or with a number of smaller groups. Randomly identifying individuals as samples of larger populations is useful in behavioral studies. Most investigators avoid changing the appearance of the head and neck of birds, because Guhl and Ortman (1953) found that hens whose appearance was altered in those areas were attacked as if they were strangers by penmates. Alterations of other parts of the body often attracted attention initially, but marked hens retained their status within the group. As indicated previously, pecking orders can be complex and involve many "pecking triangles" in which nontransitive dominance relationships exist. For example, in considering Individuals A, B, and C, it is often found that A is dominant to B and B is dominant to C, but C is dominant to A. Thus, within the pecking triangle, each bird is dominant to one and submissive to another of the triad. When several or many pecking triangles exist, it becomes difficult to assign social status ranks to the individuals involved. Although in each pair relationship one bird is dominant and the other subordinate, the quality of the relationship may vary greatly; in some pairs, the dominant individual may be extremely abusive, whereas in others, considerable tolerance towards the subordinate exists. The most common measure of status in the past has been based on the number of others in the group known to be dominated. However, to get a measure that indicates the relative frequencies of aggressive acts delivered by an individual, "dominance ratios", based on number of aggressive acts divided by total agonistic acts, were used by Craig and Guhl (1969). Dominance ratios can measure the relative status in large flocks in which only a moderate number of birds are selected randomly to be marked and observed as "focal animals." This was found to be a useful measure. Observing the sample of marked individuals one bird at a time for predetermined time periods
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REFERENCES Al-Rawi, B., and J. V. Craig, 1975. Agonistic behavior of caged chickens related to group size and area per bird. Appl. Anim. Ethol. 2:69-80. Appleby, M. C , 1983. The probability of linearity in hierarchies. Anim. Behav. 31:600-608.
Banks, E. M, D.G.M. Wood-Gush, B. O. Hughes, and N. J. Mankovich, 1979. Social rank and priority of access to resources in domestic fowl. Behav. Processes 4:197-209. Bhagwat, A. L., and J. V. Craig, 1977. Selecting for age at first egg: effects on social dominance. Poultry Sci. 56:361-363. Biswas, D. K., and J. V. Craig, 1971. Social tension indexes and egg production traits in chickens. Poultry Sci. 50:1063-1065. Blokhuis, H. J., 1986. Feather pecking in poultry: its relation with ground pecking. Appl. Anim. Behav. Sci. 16:63-67. Blokhuis, H. J., and J. G. Arkes, 1984. Some observations on the development of featherpecking in poultry. Appl. Arum. Behav. Sci. 12: 145-157. Collias, N. E., 1943. Statistical analysis of factors which make for success in initial encounters between hens. Am. Nat. 77:529-538. Collias, N. E., E. C. Collias, D. Hunsaker, and L. Minning, 1966. Locality fixation, mobility and social organization within an unconfined population of Red Jungle Fowl. Anim. Behav. 14: 550-559. Craig, J. V., 1981. Social behavior effects on spacing. Pages 32-53 in: Domestic Animal Behavior. Prentice-Hall, Inc., Englewood Cliffs, NJ. Craig, J. V., and R. A. Baruth, 1965. Inbreeding and social dominance ability in chickens. Anim. Behav. 13:109-113. Craig, J. V., and A. L. Bhagwat, 1974. Agonistic and mating behavior of adult chickens modified by social and physical environments. Appl. Anim. Ethol. 1:57-65. Craig, J. V., D. K. Biswas, and A. M. Guhl, 1969. Agonistic behaviour influenced by strangeness, crowding and heredity in female domestic fowL Anim. Behav. 17:498-506. Craig, J. V., T. P. Craig, and A. D. Dayton, 1983. Fearful behavior by caged hens of two genetic stocks. Appl. Anim. Ethol. 10:263-273. Craig, J. V., and A. M. Guhl, 1969. Territorial behavior and social interactions of pullets kept in large flocks. Poultry Sci. 48:1622-1628. Craig, J. V., M.-L. Jan, C. R. Polley, A. L. Bhagwat, and A. D. Dayton, 1975. Changes in relative aggressiveness and social dominance associated with selection for early egg production in chickens. Poultry Sci. 54:1647-1658. Craig, J. V., and H.-Y. Lee, 1989. Research note: Genetic stocks of White Leghorn type differ in relative productivity when beaks are intact versus trimmed. Poultry Sci. 68:1720-1723. Craig, J. V., and H.-Y. Lee, 1990. Beak trimming and genetic stock effects on behavior and mortality from cannibalism in White Leghorn-type pullets. Appl. Anim. Behav. Sci. 25:107-123. Craig, J. V., N. A. Okpokho, and G. A. Milliken, 1988. Floor- and cage-rearing effects on pullets' initial adaptation to multiple-hen cages. Appl. Anim. Behav. Sci. 20:319-333. Craig, J. V., L. L. Qrtman, and A. M. Guhl, 1965. Genetic selection for social dominance ability in chickens. Anim. Behav. 13:114-131. Craig, J. V., and N. C. Ramos, 1986. Competitive feeding behavior and social status in multiplehen cages. Appl. Anim. Behav. Sci. 16:69-76. Duncan, I.J.H., and D.G.M. Wood-Gush, 1971. Frus-
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in a pen with feed and water available at point sources, i.e., so that only one bird could gain access at a time. There was a significant, but not perfect, relationship between social rank and frequency and duration of feeding. However, thirsty birds did not compete at the water source. Whichever bird arrived first was allowed to drink its fill, regardless of its dominance rank. In a cage environment, when the feeder was attached outside the cage, an association between rank and access to restricted feeder space was not found (Craig and Ramos, 1986). Displacements at the opening to the feeder were frequent, and hens often achieved access by crawling under or over the bird that had been feeding. In this situation, subordinate birds were not required to face dominants that were displaced. Clearly, the level of motivation and amount of effort required to gain access to a scarce resource, as well as social status, is relevant to whether an individual gains access. A study by King (1965) indicated that frustrating situations may become so extreme with cockerels that dominant individuals do not necessarily control access. Syme (1974) has been particularly critical of using measures of ability to gain access to resources as a criterion of relative social status. Most poultry scientists interested in applied research want to know how dominance and competitive ranks are associated with each other and with wellbeing and production characteristics. The various measures discussed need to be tested for such associations. When associations are found between estimators of status and other traits, evidence is provided that needed resources may not be obtainable at desirable levels by lowerranking birds. Genetic effects, management systems, and physical and social environments are then opened to scrutiny to determine whether behavioral or other problems are causing inequities to arise.
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Cambridge University Press, New York, NY. McBride, G., 1958. The measurement of aggressiveness in the domestic hen. Anim. Behav. 6:87-91. McBride, G., 1964. Behaviour and the rational husbandry of poultry. Pages 23-26 in: Proceedings Australia Poultry Convention, 1964. McBride, G., 1971. Theories of animal spacing: the role of flight, fight, and social distance. Pages 53-68 in: Behavior and Environment. A. H. Esser, ed. Plenum Press, New York, NY. McBride, G., and F. Foenander, 1962. Territorial behaviour in flocks of domestic fowls. Nature 194:102. McBride, G., I. P. Parer, and F. Foenander, 1969. The social organization and behaviour of the feral domestic fowl. Anim. Behav. Monogr. 2: 127-181. Mench, J. A., 1988. The development of aggressive behavior in male broiler chickens: a comparison with laying-type males and the effects of feed restriction. Appl. Anim. Behav. Sci. 21:233-242. Meunier-Salaun, M. C , and J. M. Faure, 1984-1985. On the feeding behaviour of the laying hen. Appl. Anim. Behav. Sci. 13:129-141. O'Keefe, T. R., H. B. Graves, and H. S. Siegel, 1988. Social organization in caged layers: the peck order revisited. Poultry Sci. 67:1008-1014. Ortman, L. L., and J. V. Craig, 1968. Social dominance in chickens modified by genetic selection—physiological mechanisms. Anim. Behav. 16:33-37. Pamment, P., F. Foenander, and G. McBride, 1982-1983. Social and spatial organization of male behavior in mated domestic fowl. Appl. Anim. Ethol. 9:341-349. Polley, C. R., J. V. Craig, and A. L. Bhagwat, 1974. Crowding and agonistic behavior: a curvilinear relationship? Poultry Sci. 53:1621-1623. Schjelderup-Ebbe, T., 1922. Beitrage zur Socialpsychologie des Hauschuhns. Z. Psychol. 88: 225-252. SiegeL H. S., and P. B. SiegeL 1961. The relationship of social competition with endocrine weights and activity in male chickens. Anim. Behav. 9: 151-158. SiegeL P. B., 1965. Genetics of behavior: selection for mating ability in chickens. Genetics 52: 1269-1272. Syme, G. J., 1974. Competitive orders as measures of social dominance. Anim. Behav. 22:931-940. Tindell, D., and J. V. Craig, 1959. Effects of social competition on laying house performance in the chicken. Poultry Sci. 3855-105. Wennrich, G., 1974. Ethological studies of feather pecking and cannibalism in domestic chickens (Gallus domesticus) in floor management. Pages 553-554 in: Proceedings of the 15th World's Poultry Congress, New Orleans, LA. Ylander, D. M., and J. V. Craig, 1980. Inhibition of agonistic acts between domestic hens by a dominant third party. Appl. Anim. Ethol. 6: 63-69.
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tration and aggression in the domestic fowl. Arum. Behav. 19:500-504. Guhl, A. M., 1953. Social behavior of the domestic fowl. Kansas Agricultural Experiment Station Technical Bulletin 73:1-48. Guhl, A. M., 1958. The development of social organisation in the domestic chick. Anim. Behav. 652-111. Guhl, A. M., 1962. The behaviour of chickens. Pages 491-530 in: The Behaviour of Domestic Animals. E.S.E. Hafez, ed. The Williams and Wilkins Company, Baltimore, MD. Guhl, A. M., and W. C. AUee, 1944. Some measurable effects of social organization in flocks of hens. Physiol. Zool. 17:320-347. Guhl, A. M., J. V. Craig, and C. D. Mueller, 1960. Selective breeding for aggressiveness in chickens. Poultry Sci. 39:970-980. Guhl, A. M., and L. L. Ortman, 1953. Visual patterns in the recognition of individuals among chickens. Condor 55387-298. Guhl, A. M., and D. C. Warren, 1946. Number of offspring sired by cockerels related to social dominance in chickens. Poultry Sci. 25:460-472. Hale, E. B., 1948. Observations on the social behavior of hens following debeaking. Poultry Sci. 27: 591-592. Hale, E. B., and M. W. Schein, 1962. The behaviour of turkeys. Pages 531-564 in: The Behaviour of Domestic Animals. E.S.E. Hafez, ed. The Williams and Wilkins Company, Baltimore, MD. Hughes, B. O., D.G.M. Wood-Gush, and R. M. Jones, 1974. Spatial organization in flocks of domestic fowls. Arum. Behav. 22:438-445. King, M. G., 1965. Disruptions of the pecking order of cockerels concomitant with degrees of accessibility to feed. Anim. Behav. 13:504-506. Kratzer, D. D., and J. V. Craig, 1980. Mating behavior of cockerels: effects of social status, group size, and group density. Appl. Anim. Ethol. 6:49-62. Kuo, F.-L., J. V. Craig, and W. M. Muir, 1991. Selection and beak-trimming effects on behavior, cannibalism, and short-term production traits in White Leghorn pullets. Poultry Sci. 70: 1057-1068. Lee, H.-Y., and J. V. Craig, 1991. Beak trimming effects on behavior patterns, fearfulness, feathering, and mortality among three stocks of White Leghorn pullets in cages or floor pens. Poultry Sci. 70:211-221. Lee, Y.-P., and J. V. Craig, 1981. Agonistic and nonagonistic behaviors of pullets of dissimilar strains of White Leghorns when kept separately and intermingled. Poultry Sci. 60:1759-1768. Lee, Y.-P., J. V. Craig, and A. D. Dayton, 1982. The social rank index as a measure of social status and its association with egg production in White Leghorn pullets. Appl. Anim. Ethol. 8: 377-390. Lehner, P. N., 1979. Handbook of Ethological Methods. Garland STPM Press, New York, NY. Martin, P., and P. Bateson, 1986. Measuring Behavior.
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