use of pen space by broiler chickens: effects of age and pen size

Applied Animal Behaviour Science, 25 ( 1990 ) 125-136 125 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Use of Pen Space by Broi ler Chickens: Effects of Age and Pen Size

R.C. N E W B E R R Y 1 and J.W. HALL 2

IAgriculture Canada, Research Station, P.O. Box 1000, Agassiz, BC VOM 1AO (Canada) 2Agriculture Canada, Research Station, 6660 S. W. Marine Drive, Vancouver, BC V6T 1X2 (Canada)

(Accepted for publication 29 August 1989)

ABSTRACT

Newberry, R.C. and Hall, J.W., 1990. Use of pen space by broiler chickens: effects of age and pen size. Appl. Anim. Behav. Sci., 25: 125-136.

An experiment was conducted to investigate the effects of age and pen size on the use of pen space by male broiler chickens. The locations of 18 marked chickens in a large pen (407 m 2 with 3040 birds) and 10 in each of two small pens (203.5 m 2 with 1520 birds) were recorded at hourly intervals, 8 times per day, on 5 consecutive days per week, from 4 to 9 weeks of age. Results indicated that the use of pen space was non-random (P < 0.05). Chickens stayed nearer to pen walls than expected by chance in both pen sizes and during all weeks (P < 0.01 }. In addition, chickens in the large pen, although not the small pens, stayed closer to their brooding site than expected ( P < 0.01 ). The area of space occupied per day and per week declined with increasing age ( P < 0.01 ) and was not affected by pen size. However total space used from 4 to 9 weeks was greater in the large than the small pens (P < 0.05). Distance moved per hour declined with age in both pen sizes (P<0.01) . Although movements were non-random, the chickens did not restrict their movements to small areas in which they could become acquainted with their neighbours over the period from 4 to 9 weeks of age. Possible implications for broiler welfare of the lack of a well- delineated home site and continual mingling with strangers are discussed.

I N T R O D U C T I O N

It is unlikely that domestic fowl can develop and maintain social relation- ships with more than ~ 100 flock mates (Guhl, 1953 ). This raises the question of whether broiler chickens kept in flocks of several thousand birds are continually encountering strangers during their movements within the pen over the course of the rearing period. Such encounters could have an adverse effect on broiler welfare since it has been reported that repeated introduction of strangers into small groups of domestic fowl results in adrenal hypertrophy (Siegel and Siegel, 1961 ), increased plasma corticosteroid levels (Gross and Siegel, 1983 ),

Agassiz Research Station Contribution number 393.

126 R.C. NEWBERRY AND J.W. HALL

raised levels of agonistic interaction (Craig et al., 1969), reduced growth and increased heterophil:lymphocyte ratios (Anthony et al., 1988).

McBride and Foenander (1962) predicted that poultry in large flocks would restrict their movements to small areas, thereby allowing individuals to become acquainted with the other birds in the vicinity and to avoid encounters with strangers. Craig and Guhl (1969) found that individuals in a flock of 400 pullets spent disproportionate amounts of time in particular areas of their pen. They indicated that individuals won a larger proportion of agonistic interactions in the areas where they spent the most time than in other areas. Crawford (1966) reported that White Leghorn chickens which were brooded for 7 weeks in separate pens and then allowed to roam between pens did not intermingle freely, but tended to roost in the vicinity of the pen in which they had been brooded. However, Appleby et al. (1985) observed that hens in a commercial broiler breeder flock ranged over a median of 505 m 2, or 73% of the total pen area, over a 34-week period. Ranges overlapped extensively and it was consid- ered likely that the hens were continually meeting strangers during their movements around the pen. Hughes et al. (1974) reported that individuals in flocks of up to 600 hens were generally seen at least once in all the sections of a 70- m 2 pen over a 14-h period. They suggested that the low light intensity in the pen (0.25 lux) allowed birds to move around the pen with impunity because it was too dark for them to be recognized as strangers.

There is a lack of information regarding the movements of broiler chickens kept in large flocks. Such information could be of practical value in predicting appropriate spacing of equipment within pens, possible biases in bird sampling procedures and transmission rates of certain diseases or behavioural vices throughout a flock. The aim of this study was to examine the effects of age and pen size on the use of pen space by individual male broiler chickens during a 9-week rearing period. Measurements were made of the area of pen space used, randomness of space use, degree of preference for areas near pen walls, degree of attachment to the brooding site, behavioural activity and distance moved per hour.

ANIMALS, M A T E R I A L S AND M E T H O D S

The investigation was conducted in two 34.2 X 11.9-m light-proof rooms, each equipped with an identical lay-out of 4 gas brooders, 112 tube feeders (pan diameter 35.6 cm, 1-13 days; 41.9 cm, 14-63 days), 32 water troughs (234 cm long) and 16 incandescent light bulbs. The floor of each room was covered with a 5-cm deep layer of wood shavings. One room was assigned to the large (34.2 X 11.9 m) pen size treatment; the other room was divided into two small (17.1Xll.9 m) pens (Fig. 1). The walls of each pen were marked with grid numbers at 1-m intervals so that locations within the pen could be specified by an x and y coordinate to the nearest metre.

USE OF PEN SPACE BY BROILER CHICKENS 127

F F F

F F F

F F

F t F F 0 0

F F F F

F

F

F

F

F

F 0

F F

F

0

F

F F

F

F I B ° F

F F

F F F F

0

F F

F F F F

F

F O

F

F F

17.1 m

Fig. 1. Lay-ou t of small pen showing locations of feeders (F), wa te r t roughs ( [ ), b rooders (B ) and i n c a n d e s c e n t light bulbs (o) . The large pen was m a d e up of two small pens joined end to end.

A total of 6080 Peterson X Arbor Acre male 1-day-old chicks, vaccinated against Marek's disease, was obtained from a commercial hatchery. Seven hundred and sixty randomly selected chicks were placed in a corral under each brooder, giving 3040 chicks in the large pen and 1520 chicks in each small pen. At 7 days, wing tags and coloured dye were applied to 10 randomly selected chicks per brooder, using different colours for each brooder group. Corrals were then removed, allowing chicks to move throughout their respective pens.

The light intensity was set at 10 lux at 1 day and reduced to 5 lux at 35 days. Light readings were made at shavings level directly beneath each light bulb. Timers were set to provide a daily 1-h period of darkness. The temperature under the brooders was reduced gradually from 35°C at 1 day to 25°C at 21 days, when brooders were switched off and raised to ceiling height. The maxi- mum room temperature recorded between 21 and 63 days was 33 ° C, and the minimum was 17 o C. Feed and water were available ad libitum and all chickens were fed on a standard dietary regimen (23% protein starter, 1-21 days; 20% grower, 22-42 days; 18% finisher, 43-63 days). Mortality checks were conducted twice daily.

At 21 days, the first five wing-tagged chickens located from each brooder group were marked for observation purposes by applying a numbered 7 × 4-cm polypropylene wing badge to each wing and spraying the chicken's back with food colouring. (Ten chicks per brooder had been marked prior to release from the corrals to allow for possible death and marking losses between 7 and 21 days, and to facilitate rapid re-location of five of the birds per brooder within the large flocks at 21 days. ) This gave a total of 20 individually marked chickens in the large pen and 10 in each small pen. Scan sampling of these chickens was conducted at hourly intervals, 8 times per day, on 5 consecutive days per week, between 24 and 63 days of age. During each scan, the location (x and y


coordinates) and the behaviour of each chicken when first spotted were recorded on a map by an observer moving slowly and quietly through the pen. The behaviour categories were feeding (at feeder), drinking (at drinker), walking (including all locomotion ), standing and lying. At 63 days, ~ 200 randomly selected chickens were weighed individually in the large pen and ~ 100 in each small pen.

Methods of analysis

Two measures of the home range size, or area of pen space used by individual chickens, were calculated. The area of the minimum convex polygon enclosing all the points where a bird was observed was calculated using the method of Jarvis (1973). The continuous path area was calculated as the sum of the grid areas occupied by a bird assuming tha t he traversed, in a straight line, all grid areas between the two in which he was observed in successive scans. This method allowed for the possibility tha t a home range could be hollow or in- dented (e.g. if a bird avoided the centre of the pen). Daily, weekly and total (4-9 weeks) areas were determined. Areas were t ransformed to square roots to stabilize the variance for analysis of variance.

To determine whether birds used grid locations at random or tended to pre- fer certain locations, the weekly frequency with which a bird was observed in each grid area was tested against a Poisson distribution. It was assumed that scans were independent and that, if locations were selected at random, the limiting distribution of the number of observations per grid area would tend to the Poisson since the number of grid areas was large relative to the number of observations made each week. The dispersion index (s2/y; Sokal and Rohlf, 1981 ) for each bird and week was multiplied by the d.f. to get the Z 2 value used in the test for dispersion (Maxwell, 1961 ). The effects of age and pen size were examined by analysis of variance using the X 2 values t ransformed to s tandard normal variates (Z).

To ascertain whether chickens were found near pen walls more often than would be expected if all areas of the pen were used equally, the observed cumulative distribution of distances of marked birds from the nearest wall was compared with the theoretical ( random) distribution using the Kolmogorov- Smirnov one sample test (Conover, 1971 ). Separate tests were conducted for each pen size and week. Pens were not compared because the distribution func- tions were dependent on pen size.

The influence of the location of brooding in Week 1 on locations occupied in Weeks 4-9 was examined by calculating the mean x and y coordinates of each marked bird in each week (mean of 40 observations ) and determining whether the bird was closest to its own or another brooder location. Since there were four brooders in the large pen and two in each small pen, the probability tha t a randomly selected position would be closest to a particular brooder was 25%


in the large pen and 50% in the small pens. X 2 tests were used to compare the observed number of birds which were closest to their home brooder with the number expected if brooding location had no effect on subsequent locations occupied.

The effects of behaviour in the previous scan, pen size and age on the distribution of behaviour among feeding, drinking, walking, standing and lying were analysed by logit analysis using the Statistical Analysis Systems (1985) pro- gram CATMOD. Analysis of variance was used to investigate the effects of pen size, age and behaviour in consecutive scans on the distance moved between the scans.

Two marked birds in the large pen died during the experiment. The partial results from these birds were excluded from the analysis. The effect of pen size on body weight at 63 days was examined by analysis of variance.

R E S U L T S

Home range sizes were usually smaller when measured by the continuous path method than the minimum convex polygon method (Table 1 ), but the results of the analysis of variance on pen size and age effects were similar for both methods (Table 2 ). Pen size had a significant effect on the total area of space used by chickens from 4 to 9 weeks (P < 0.05 ), with chickens in the large pen using more space than chickens in the small pens. Although the area occupied each week was relatively small, the centre of the home range tended to drift over time, such that a relatively large area was covered over the course of the experiment (Fig. 2 ). Pen size had no significant effect on daily and weekly home ranges, but there was considerable variation among birds within pens (Fig. 2). Daily and weekly home ranges decreased significantly as the birds grew older ( P < 0.01).

Weekly usage of pen space by most birds was non-random (i.e. P<0.05 for the X 2 test ). Of the 38 birds tested, 63.2 % showed non-random use of pen space in all 6 weeks of observation, 26.3% in 5 of the 6 weeks, and the remaining 10.5% in 4 of the 6 weeks. The degree of non-randomness, as measured by the transformed normal deviates (Z), was not affected by pen size (large pen, Z = 10.4 + 1.13; small pens, Z = 8 . 1 + 1.07), but increased with age (7.6, 5.2, 7.7, 8.4, 11.3 and 14.8 from 4 to 9 weeks, respectively; SE-- 1.05; P < 0.01 ).

Chickens tended to stay nearer to walls than expected by chance. The observed distribution for each pen size was significantly different from the random distribution in all weeks ( P < 0.01 ).

In the large pen, the centre of the weekly home range was closer to the home brooder than another brooder in 37% of the 108 bird×week combinations. This was more than the 25% expected by chance (X2= 8.4, d.f. = 1, P < 0.01 ). In the small pens, chickens were closer to their home brooder in 45% of the 120 bird × week combinations, which was not significantly different than the


TABLE 1

Effects of pen size, age, time period and method of calculation on average (back-transformed) home range size (m 2 ) of male broiler chickens

Time period Age Minimum polygon Continuous path (weeks)

Large pen Small pen Large pen Small pen

Daily (8 scans per bird)

Weekly (40 scans per bird)

Total (240 scans per bird)

4 27.6 25.3 19.5 18.5 5 25.0 20.8 19.2 17.1 6 18.9 15.3 16.0 13.8 7 16.7 16.1 14.5 13.9 8 13.0 9.5 12.8 10.4 9 8.9 7.0 10.4 8.9

Mean 18.3 15.7 15.2 13.6

4 141.8 111.7 81.6 72.7 5 128.4 102.5 79.3 68.6 6 83.9 74.1 60.8 54.1 7 81.3 74.5 57.5 53.1 8 68.8 53.4 51.5 39.5 9 43.6 40.8 35.8 31.8

Mean 91.3 76.2 61.1 53.3

4-9 258.4 167.3 193.8 150.3

Pen area (m 2) 407.0 203.5 407.0 203.5

50% expected by chance (X 2 = 0.6, d.f. = 1). There was no evidence of differences among weeks in either pen size (large pen X2--0.8, small pens X2=4.4, d.f.=5).

The behaviour observed in a particular scan depended on pen size and age, but not on the behaviour in the previous scan (Table 3). The proportion of time spent lying down was higher in the small pens than the large pen. In both pen sizes, lying increased with age at the expense of other behavioural activities.

The average distance moved between scans depended on the time elapsed between scans (3.22, 5.55 and 7.08 m for elapsed times of 1, 17 and 65 h, respectively; P < 0.01); therefore only distances moved between hourly scans within days were investigated in detail. The distance moved per hour was related to age, and to behaviour in the previous and current scans (Table 4). From 4 to 9 weeks, the average distances moved per hour were 4.51, 4.16, 3.45, 3.25, 2.77 and 2.34 m, respectively ( P < 0.01). The distance moved was least


T A B L E 2

Analysis of variance of daily, weekly and total home range size (transformed to square root) measured by the minimum polygon and continuous path methods

Source d.f. Daily Weekly Total

Mean F Mean F square square

Mean F square

Minimum polygon Pen ~ 1 32.0 1.1 34.5 1.6 93.5 Birds (pen) 36 30.5 21.8 4.9

19.1"

Week 5 143.4 28.5** 118.4 24.3** Pen × week 5 1.3 0.3 2.0 0.4 BirdXweek (pen) 180 5.0 4.9

Residual error 912 2.7

Continuous path Pen 1 14.0 1.7 15.3 1.8 26.1 Birds (pen) 36 8.1 8.5 3.6

7.3*

Week 5 44.2 34.9** 47.7 25.5** Pen X week 5 0.5 0.4 0.4 0.2 Bird X week (pen) 180 1.3 1.9

Residual error 912 0.6

~Pen size. *P < 0.05; **P < 0.01.

1 2

7'~i / ...... . I,

7 \ \ / / / /

3

L e g e n d : W e e k 4 - - W e e k 7

W e e k 5 . . . . . W e e k 8 . . . . . . .

W e e k 6 - - - - W e e k 9 . . . . . . . . . . .

Fig. 2. Minimum polygon areas occupied each week by three marked chickens (1-3) in the large pen.


T A B L E 3

Dis t r ibut ion of behaviour among feeding (F) , dr inking (D), walking (W), s tanding (S) and lying (L) (% of scans)

Age Large pen size Small pen size ( weeks )

F D W S L F D W S L

4 8.5 5 6.7 6 6.0 7 5.8 8 4.2 9 2.2

Logit analysis:

2.4 7.6 16.3 65.3 8.6 2.8 5.6 13.8 69.3 2.8 7.2 19.4 63.9 9.0 3.8 5.8 13.1 68.4 3.3 5.6 10.7 74.4 6.9 2.3 2.9 8.8 79.3 3.6 3.9 9.6 77.1 5.6 3.0 3.1 4.8 83.5 2.6 1.9 7.4 83.9 5.3 1.3 1.8 3.1 88.6 2.4 1.3 5.3 88.9 1.6 1.5 0.8 4.9 91.3

Source d.f. Z 2 Pen size 4 33.1"* Week 20 334.8** Previous behaviour 16 26.2 Residual 196 220.4

**P < 0.01.

TABLE 4

Analysis of variance of distance moved between hourly scans

Source d.f. Mean square F

Pen size 1 214.8 2.0 Bird (pen size) 36 105.3

Week 5 729.9 119.4** Previous behaviour 4 34.2 5.6** Current behaviour 4 45.0 7.4** Pen size × week 5 11.0 1.8 Previous × current 16 9.5 1.6 Residual error 7908 6.1

**P < 0.01.

T A B L E 5

Effect of behaviour in previous and current scans on mean distance moved (m) between hourly scans

Behaviour Feeding Dr inking Walking S tanding Lying

Previous 3.19 3.34 4.34 3.68 2.95 Current 3.29 3.21 4.40 3.79 2.94


when the behaviour in the previous or current scan was lying and greatest when it was walking (Table 5 ). Movements were not limited to travel to the nearest feeder or drinker. On average, birds moved > 3 m in the hour preceding feeding or drinking behaviour, although pens were arranged such that birds were never > 2 m away from the nearest feeder and 2.4 m away from the nearest drinker. Longer movements from one area to another were observed when birds moved to avoid caretakers conducting mortality checks, filling feeders, etc., and when groups of young birds ran playfully (frolicked) along the pen. Pen size had no detectable effect on distance moved per hour.

Body weight at 63 days was not significantly affected by pen size (large pen x = 3.65 kg, small pens x-- 3.60 kg, SE = 0.024, P > 0.05). Cumulative mortality to 63 days was 6.9% in the large pen and 6.0% in the small pens.

D I S C U S S I O N

The results indicate that values obtained for the home range size of chickens are highly dependent on the method of calculation and the time period over which data are collected, thus making comparisons between studies difficult. However it would appear that the young male broiler chickens observed in this study were not remaining within an area small enough that they could become familiar with the other chickens in the vicinity. Evidently, considerable mixing of flock members was taking place over time. This finding is in agreement with results obtained from a large flock of adult broiler breeder hens over a 34-week period (Appleby et al., 1985) and is contrary to the reported defence of terri- tories by small groups of adult fowl with well-established social hierarchies when faced with intruders (McBride and Foenander, 1962; Collias et al., 1966 ).

The small pen size (203.5 m 2) restricted the amount of space used over a 6- week period by comparison with the large pen size (407 m 2 ). This was probably because birds could move less distance before contacting an end wall and being reflected back towards areas they had already spent time in. The tendency for chickens to stay close to the walls could explain why birds in both the large and small pens did not use a larger proportion of the available pen area. Greater use of space near walls has also been reported for adult cocks kept in small pens (Pamment et al., 1983 ) and adult hens kept in a large outdoor enclosure (Keeling, 1987). These findings suggest that pen shape will affect the distribution of birds within pens of the same floor area.

It is likely that the decline in home range size, walking time and distance moved per hour with increasing age were related. These findings could be associated with increased difficulty in walking with advancing age (Newberry et al., 1986), a decrease in frolicking behaviour (Dawson and Siegel, 1967), a reduction in the distance moved by older chickens when disturbed (R. New- berry, unpublished observation, 1988) and the increased body mass of older chickens, which may act as a physical barrier to individuals attempting to walk from one location to another. The possibility that, with increasing age, the


chickens were limiting their movements as a result of social pressure (McBride and Foenander, 1962; Craig and Guhl, 1969) cannot be ruled out, although Mench (1988) observed that pecking and threatening behaviour by broilers fed ad libitum remained extremely low between 4 and 9 weeks of age. The finding of a reduction in movement with increasing age is contrary to results obtained from broods of young domestic fowl living in the wild, whose movements appear to be influenced by the movements of the hen, the distribution of food, and the need to avoid predators and roost in a safe location during the night (McBride et al., 1969; Wood-Gush et al., 1978).

In most cases, the chickens observed in this study used the pen space non- randomly. Examination of the data suggested that this was the result of birds staying in one area for a long period rather than repeatedly leaving and return- ing to a favoured area. The decrease in randomness with increasing age was probably associated with the increase in time spent lying down as the birds aged. Similar results were obtained in a study of laying hens (Hughes et al., 1974), although the proportion of birds exhibiting non-random movements was lower in that study.

It was not clear why birds in the large pen tended to be found near their home brooder whereas birds in the small pens did not. Attachment to the brooding area for use as a roosting site has been reported previously (Crawford, 1966; Tribe, 1980). Site a t tachment appears to be stronger the longer a group is kept confined to the brooding area (Tribe, 1980) and may be enhanced by the presence of distinctive environmental features to which the birds become imprinted (Gvaryahu et al., 1987). In the present study, chicks were corralled under a specific brooder for only 1 week and all brooder sites were identical; therefore the birds may have had difficulty in distinguishing their own brooding site from another, particularly after the brooders were raised. There was no evidence that the birds were using different areas of the pen for different activities.

The finding that the proportion of time spent in different activities was affected by pen size is of interest since differences in lying time could have subtle effects on energy use, thereby influencing productivity. Nevertheless, body weight at 9 weeks was not affected by pen size, although no measurements were made of feed consumption. The observation of an increase in lying time with increasing age at the expense of other activities is in agreement with previous results (Newberry et al., 1988).

The male broiler chickens observed in this study did not exhibit strong site at tachments during the period from 4 to 9 weeks of age. Therefore the predic- tion that poultry in large flocks would limit their movements to small areas in which they could recognize their neighbours (McBride and Foenander, 1962) was not confirmed for these birds. Implications for the welfare of broilers kept in large flocks are not clear. Young chickens may have no desire to remain in, or return to, a specific site when kept in a very uniform environment. They


may feel comfortable in all areas because different areas, and the chickens in those areas, appear equally familiar. Conversely, movements from one area to another may be due to the inability of chickens to distinguish or relocate a home area in the very uniform pen environment following disturbance by caretakers. This may result in increased social tension or fear as a result of continual mingling with strangers and loss of the home site. If so, welfare would be compromised. In this case, the recommendation that site attachment should be promoted by altering pen design to make different areas distinguishable from one another (Tribe, 1980) would be valid. Further research will be re- quired to determine the effects of pen design on broiler welfare.

In conclusion, both age and pen size affected the amount of pen space used and distance travelled by male broilers kept in relatively large floor pens at a commercial stocking density. Proximity to walls and the location of the home brooder also influenced the use of pen space by the chickens. Movement did not appear to be limited by the spacing of feeders and water troughs used in this study. Mixing among flock members probably contributes to uniformity among birds at different locations within pens and may influence the spread of certain diseases and vices, such as cannibalism, within a pen.

ACKNOWLEDGEMENTS

The technical assistance of T. Yule, L. Struthers and the poultry crew is gratefully acknowledged.

REFERENCES

Anthony, N.B., Katanbaf, M.N. and Siegel, P.B., 1988. Responses to social disruption in two lines of White Leghorn chickens. Appl. Anim. Behav. Sci., 21: 243-250.

Appleby, M.C., Maguire, S.N. and McCrae, H.E., 1985. Movement by domestic fowl in commercial flocks. Poult. Sci., 64: 48-50.

Collias, N.E., Collias, E.C., Hunsaker, D. and Minning, L., 1966. Locality fixation, mobility and social organization within an unconfined population of Red Jungle Fowl. Anim. Behav., 14: 550-559.

Conover, W.J., 1971. Practical Nonparametric Statistics. Wiley, New York. Craig, J.V. and Guhl, A.M., 1969. Territorial behavior and social interactions of pullets kept in

large flocks. Poult. Sci., 48: 1622-1628. Craig, J.V., Biswas, D.K. and Guhl, A.M., 1969. Agonistic behaviour influenced by strangeness,

crowding and heredity in female domestic fowl (GaUus gaUus ). Anim. Behav., 17: 498-506. Crawford, R.D., 1966. Movement of birds within large flocks of juvenile White Leghorns as mea-

sured by roosting locations. Poult. Sci., 45: 489-491. Dawson, J.S. and Siegel, P.B., 1967. Behavior patterns of chickens to ten weeks of age. Poult. Sci.,

46: 615-622. Gross, W.B. and Siegel, H.S., 1983. Evaluation of the heterophil/lymphocyte ratio as a measure

of stress in chickens. Avian Dis., 27: 972-979. Guhl, A.M., 1953. Social behavior of the domestic fowl. Kans. Agric. Exp. Stn. Tech. Bull. No. 73.


Gvaryahu, G., Snapir, N. and Robinzon, B., 1987. Application of the filial imprinting phenomenon to broiler chicks at a commercial farm. Poult. Sci., 66: 1564-1566.

Hughes, B.O., Wood-Gush, D.G.M. and Morley-Jones, R., 1974. Spatial organization in flocks of domestic fowls. Anim. Behav., 22: 438-445.

Jarvis, R.A., 1973. On the identification of the convex hull of a finite set of points in the plane. Inf. Process. Lett., 2: 18-21.

Keeling, L.J., 1987. Social spacing in domestic fowl. Ph.D. Thesis, University of Edinburgh. Maxwell, A.E., 1961. Analysing Qualitative Data. Methuen, London. McBride, G. and Foenander, F., 1962. Territorial behaviour in flocks of domestic fowls. Nature

(London), 194: 102. McBride, G., Parer, I.P. and Foenander, F., 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 chicks: a comparison

with laying-type males and the effects of feed restriction. Appl. Anita. Behav. Sci., 21: 233- 242.

Newberry, R.C., Hunt, J.R. and Gardiner, E.E., 1986. Light intensity effects on performance, activity, leg disorders, and sudden death syndrome of roaster chickens. Poult. Sci., 65: 2232- 2238.

Newberry, R.C., Hunt, J.R. and Gardiner, E.E., 1988. Influence of light intensity on behavior and performance of broiler chickens. Poult. Sci., 67: 1020-1025.

Pamment, P., Foenander, F. and McBride, G., 1983. Social and spatial organization of mate behaviour in mated domestic fowl. Appl. Anim. Ethol., 9: 341-349.

Siegel, H.S. and Siegel, P.B., 1961. Relationship of social competition with endocrine weights and activity in male chickens. Anim. Behav., 9: 151-158.

Sokal, R.R. and Rohlf, F.J., 1981. Biometry. Freeman, San Francisco. Statistical Analysis Systems, 1985. SAS User's Guide: Statistics. Version 5 Edition. SAS Institute

Inc., Cary, NC. Tribe, A., 1980. Environmental design and site attachment in flocks of broiler chickens. M. Ag.

Sci. Thesis, University of Queensland. Wood-Gush, D.G.M., Duncan, I.J.H. and Savory, C.J., 1978. Observations on the social behaviour

of domestic fowl in the wild. Biol. Behav., 3: 193-205.

use of pen space by broiler chickens: effects of age and pen size

Documents